[Levinson W.]Review of Medical Microbiology and Immunology

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C lose Window Author Warren Levinson, MD, PhD Professor of Microbiology Department of Microbiology and Immunology University of C alifornia, San Francisco San Francisco, C alifornia / 545 C lose Window Copyright Information Review of Medical Microbiology & Immunology, Eleventh Edition C opyright © 2010 by The McGraw-Hill C ompanies, Inc All rights reserved Printed in the United States of America Except as permitted under the United States C opyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system, without the prior written permission of the publisher Previous editions copyright © 2008, 2006, 2004, 2002, 2000 by The McGraw-Hill C ompanies, Inc., and copyright © 1998, 1996, 1994, 1992, 1989 by Appleton & Lange ISBN 978-0-07-170028-3 MHID 0-07-170028-5 ISSN 1042-8070 Notice Medicine is an ever-changing science As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy are required The authors and the publisher of this work have checked with sources believed to be reliable in their efforts to provide information that is complete and generally in accord with the standards accepted at the time of publication However, in view of the possibility of human error or changes in medical sciences, neither the authors nor the publisher nor any other party who has been involved in the preparation or publication of this work warrants that the information contained herein is in every respect accurate or complete, and they disclaim all responsibility for any errors or omissions or for the results obtained from use of the information contained in this work Readers are encouraged to confirm the information contained herein with other sources For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this work is accurate and that changes have not been made in the recommended dose or in the contraindications for administration This recommendation is of particular importance in connection with new or infrequently used drugs / 545 C lose Window Preface This book is a concise review of the medically important aspects of microbiology and immunology It covers both the basic and clinical aspects of bacteriology, virology, mycology, parasitology, and immunology Its two major aims are (1) to assist those who are preparing for the USMLE (National Boards) and (2) to provide students who are currently taking medical microbiology courses with a brief and up-todate source of information My goal is to provide the reader with an accurate source of clinically relevant information at a level appropriate for those beginning their medical education This new edition presents current, medically important information in the rapidly changing fields of microbiology and immunology It contains many color micrographs of stained microorganisms as well as images of important laboratory tests It also includes a chapter on ectoparasites, such as the mite that causes scabies, and current information on antimicrobial drugs and vaccines These aims are achieved by utilizing several different formats, which should make the book useful to students with varying study objectives and learning styles: A narrative text for complete information A separate section containing summaries of important microorganisms for rapid review of essentials Sample questions in the USMLE (National Board) style, with answers A USMLE (National Board) practice examination consisting of 80 microbiology and immunology questions The questions are incorporated into a clinical case format and simulate the computer-based examination Answers are provided C linical case vignettes to provide both clinical information and practice for the USMLE A section titled "Pearls for the USMLE" describing important epidemiological information helpful in answering questions on the USMLE Many images of clinically important lesions seen in patients with infectious diseases described in this book are available on the McGrawHill Online Learning C enter's Web site (www.langetextbooks.com) The lesions are shown in a gallery The following features are included to promote a successful learning experience for students using this book: The information is presented succinctly, with stress on making it clear, interesting, and up to date There is strong emphasis in the text on the clinical application of microbiology and immunology to infectious diseases In the clinical bacteriology and virology sections, the organisms are separated into major and minor pathogens This allows the student to focus on the clinically most important microorganisms Key information is summarized in useful review tables Important concepts are illustrated by figures using color Important facts called "Pearls" are listed at the end of each basic science chapter The 654 USMLE (National Board) practice questions cover the important aspects of each of the subdisciplines on the USMLE: Bacteriology, Virology, Mycology, Parasitology, and Immunology A separate section containing extended matching questions is included In view of the emphasis placed on clinical relevance in the USMLE, another section provides questions set in a clinical case context Brief summaries of medically important microorganisms are presented together in a separate section to facilitate rapid access to the information and to encourage comparison of one organism with another Fifty clinical cases are presented as unknowns for the reader to analyze in a brief, problem-solving format These cases illustrate the importance of basic science information in clinical diagnosis Seventy color images depicting clinically important findings, such as Gram stains of bacteria, electron micrographs of viruses, and microscopic images of fungi, protozoa, and worms, are included in the text After teaching both medical microbiology and clinical infectious disease for many years, I believe that students appreciate a book that presents the essential information in a readable, interesting, and varied format I hope you find this book meets those criteria Warren Levinson, MD, PhD San Francisco, C alifornia May 2010 / 545 Print Close W indow Note: Large im ages and tables on this page m ay necessitate printing in landscape m ode Copyright © The McGraw-Hill Companies A ll rights reserved Review of Medical Microbiology and Immunology > Chapter Bacteria Com pared with O ther Microorganism s > AGENT S The agents of human infectious diseases belong to five major groups of organisms: bacteria, fungi, protozoa, helminths, and viruses The bacteria belong to the prokaryote kingdom, the fungi (yeasts and molds) and protozoa are members of the kingdom of protists, and the helminths (w orms) are classified in the animal kingdom (Table 1–1) The protists are distinguished from animals and plants by being either unicellular or relatively simple multicellular organisms The helminths are complex multicellular organisms that are classified as metazoa w ithin the animal kingdom Taken together, the helminths and the protozoa are commonly called parasites Viruses are quite distinct from other organisms—they are not cells but can replicate only w ithin cells Table 1–1 Biologic Relationships of Pathogenic Microorganisms Kingdom Pathogenic Microorganisms Type of Cells Animal Helminths Eukaryotic Plant None Eukaryotic Protist Protozoa Eukaryotic Fungi Eukaryotic Prokaryote Bacteria Viruses Noncellular Prokaryotic IMPORT ANT FEAT URES Many of the essential characteristics of these organisms are described in Table 1–2 One salient feature is that bacteria, fungi, protozoa, and helminths are cellular, w hereas viruses are not This distinction is based primarily on three criteria: Structure Cells have a nucleus or nucleoid (see below ), w hich contains DNA; this is surrounded by cytoplasm, w ithin w hich proteins are synthesized and energy is generated Viruses have an inner core of genetic material (either DNA or RNA) but no cytoplasm, and so they depend on host cells to provide the machinery for protein synthesis and energy generation Method of replication Cells replicate either by binary fission or by mitosis, during w hich one parent cell divides to make tw o progeny cells w hile retaining its cellular structure Prokaryotic cells, e.g., bacteria, replicate by binary fission, w hereas eukaryotic cells replicate by mitosis In contrast, viruses disassemble, produce many copies of their nucleic acid and protein, and then reassemble into multiple progeny viruses Furthermore, viruses must replicate w ithin host cells because, as mentioned above, they lack protein-synthesizing and energy-generating systems W ith the exception of rickettsiae and chlamydiae, w hich also require living host cells for grow th, bacteria can replicate extracellularly Nature of the nucleic acid Cells contain both DNA and RNA, w hereas viruses contain either DNA or RNA but not both Table 1–2 Comparison of Medically Important Organisms Characteristic Viruses Bacteria Fungi Protozoa and Helminths Cells No Yes Yes Yes Approximate diameter 0.02–0.2 ( m)1 1–5 3–10 (yeasts) 15–25 (trophozoites) Nucleic acid Either DNA or RNA Both DNA and RNA Both DNA and RNA Both DNA and RNA Type of nucleus None Prokaryotic Eukaryotic Eukaryotic Ribosomes Absent 70S 80S 80S Mitochondria Absent Absent Present Present Nature of outer surface Protein capsid and lipoprotein envelope Rigid w all containing peptidoglycan Rigid w all containing Flexible membrane chitin / 545 surface envelope peptidoglycan chitin Motility None Some None Most Method of replication Not binary fission Binary fission Budding or mitosis Mitosis For comparison, a human red blood cell has a diameter of m Yeasts divide by budding, w hereas molds divide by mitosis Helminth cells divide by mitosis, but the organism reproduces itself by complex, sexual life cycles EUKARYOT ES & PROKARYOT ES Cells have evolved into tw o fundamentally different types, eukaryotic and prokaryotic, w hich can be distinguished on the basis of their structure and the complexity of their organization Fungi and protozoa are eukaryotic, w hereas bacteria are prokaryotic The eukaryotic cell has a true nucleus w ith multiple chromosomes surrounded by a nuclear membrane and uses a mitotic apparatus to ensure equal allocation of the chromosomes to progeny cells The nucleoid of a prokaryotic cell consists of a single circular molecule of loosely organized DNA, lacking a nuclear membrane and mitotic apparatus (Table 1–3) Table 1–3 Characteristics of Prokaryotic and Eukaryotic Cells Characteristic Prokaryotic Bacterial Cells Eukaryotic Human Cells DNA w ithin a nuclear membrane No Yes Mitotic division No Yes DNA associated w ith histones No Yes Chromosome number One More than one Membrane-bound organelles, such as mitochondria and lysosomes No Yes Size of ribosome 70S 8OS Cell w all containing peptidoglycan Yes No In addition to the different types of nuclei, the tw o classes of cells are distinguished by several other characteristics: Eukaryotic cells contain organelles, such as mitochondria and lysosomes, and larger (80S) ribosomes, w hereas prokaryotes contain no organelles and smaller (70S) ribosomes Most prokaryotes have a rigid external cell w all that contains peptidoglycan, a polymer of amino acids and sugars, as its unique structural component Eukaryotes, on the other hand, not contain peptidoglycan Either they are bound by a flexible cell membrane or, in the case of fungi, they have a rigid cell w all w ith chitin, a homopolymer of Nacetylglucosamine, typically forming the framew ork The eukaryotic cell membrane contains sterols, w hereas no prokaryote, except the w all-less Mycoplasma, has sterols in its membranes Motility is another characteristic by w hich these organisms can be distinguished Most protozoa and some bacteria are motile, w hereas fungi and viruses are nonmotile The protozoa are a heterogeneous group that possess three different organs of locomotion: flagella, cilia, and pseudopods The motile bacteria move only by means of flagella T ERMINOLOGY Bacteria, fungi, protozoa, and helminths are named according to the binomial Linnean system, w hich uses genus and species, but viruses are not so named For example, regarding the name of the w ell-know n bacteria Escherichia coli, Escherichia is the genus and coli is the species name Similarly, the name of the yeast Candida albicans consists of Candida as the genus and albicans as the species But viruses typically have a single name such as poliovirus, measles virus, or rabies virus Some viruses have names w ith tw o w ords such as herpes simplex virus, but those not represent genus and species PEARLS The agents of human infectious diseases are bacteria, fungi (y easts and m olds), protozoa, helm inths (worm s), and v iruses Bacterial cells have a prokary otic nucleus, w hereas human, fungal, protozoan, and helminth cells have a eukary otic nucleus Viruses are not cells and not have a nucleus All cells contain both DNA and RNA, w hereas viruses contain either DNA or RNA, not both Bacterial and fungal cells are surrounded by a rigid cell w all, w hereas human, protozoan, and helminth cells have a / 545 Bacterial and fungal cells are surrounded by a rigid cell w all, w hereas human, protozoan, and helminth cells have a flexible cell membrane The bacterial cell w all contains peptidogly can, w hereas the fungal cell w all contains chitin PRACT ICE QUEST IONS: USMLE & COURSE EXAMINAT IONS Questions on the topics discussed in this chapter can be found in the Interactive Self Assessment C opyright © The McGraw-Hill C ompanies All rights reserved Privacy Notice Any use is subject to the Terms of Use and Notice / 545 Print Close W indow Note: Large im ages and tables on this page m ay necessitate printing in landscape m ode Copyright © The McGraw-Hill Companies A ll rights reserved Review of Medical Microbiology and Immunology > Chapter Structure of Bacterial Cells > SHAPE & SIZE Bacteria are classified by shape into three basic groups: cocci, bacilli, and spirochetes (Figure 2–1) The cocci are round, the bacilli are rods, and the spirochetes are spiral-shaped Some bacteria are variable in shape and are said to be pleomorphic (many-shaped) The shape of a bacterium is determined by its rigid cell w all The microscopic appearance of a bacterium is one of the most important criteria used in its identification Figure 2–1 Bacterial morphology A: C occi in clusters, e.g., Staphylococcus (A-1); chains, e.g., Streptococcus (A-2); in pairs with pointed ends, e.g., Streptococcus pneumoniae (A-3); in pairs with kidney bean shape, e.g., Neisseria (A-4) B: Rods (bacilli): with square ends, e.g., Bacillus (B-1); with rounded ends, e.g., Salmonella (B-2); club-shaped, e.g., Corynebacterium (B-3); fusiform, e.g., Fusobacterium (B-4); comma-shaped, e.g., Vibrio (B-5) C: Spirochetes: relaxed coil, e.g., Borrelia (C -1); tightly coiled, e.g., Treponema (C -2) (Modified and reproduced with permission from Joklik WK et al Zinsser Microbiology 20th ed Originally published by Appleton & Lange C opyright 1992 by McGraw-Hill.) In addition to their characteristic shapes, the arrangement of bacteria is important For example, certain cocci occur in pairs (diplococci), some in chains (streptococci), and others in grapelike clusters (staphylococci) These arrangements are determined by the orientation and degree of attachment of the bacteria at the time of cell division The arrangement of rods and spirochetes is medically less important and w ill not be described in this introductory chapter Bacteria range in size from about 0.2 to m (Figure 2–2) The smallest bacteria (Mycoplasma) are about the same size as the largest viruses (poxviruses), and are the smallest organisms capable of existing outside a host The longest bacteria rods are the size of some yeasts and human red blood cells (7 m) Figure 2–2 / 545 Sizes of representative bacteria, viruses, yeasts, protozoa, and human red cells The bacteria range in size from Mycoplasma, the smallest, to Bacillus anthracis, one of the largest The viruses range from poliovirus, one of the smallest, to poxviruses, the largest Yeasts, such as Candida albicans, are generally larger than bacteria Protozoa have many different forms and a broad size range HIV, human immunodeficiency virus (Modified and reproduced with permission from Joklik WK et al Zinsser Microbiology 20th ed Originally published by Appleton & Lange C opyright 1992 McGraw-Hill.) ST RUCT URE The structure of a typical bacterium is illustrated in Figure 2–3, and the important features of each component are presented in Table 2–1 Figure 2–3 Bacterial structure (Modified with permission from Ryan et al Sherris Medical Microbiology 4th ed C opyright 2004 McGraw-Hill.) Table 2–1 Bacterial Structures Structure Chemical Composition Function Sugar backbone w ith peptide side chains that are crosslinked Gives rigid support, protects against osmotic pressure, is the site of action of penicillins and cephalosporins, and is degraded by lysozyme Essential components Cell w all Peptidoglycan / 545 Outer membrane of Lipid A gram-negative bacteria Polysaccharide Surface fibers of Teichoic acid gram-positive bacteria Toxic component of endotoxin Major surface antigen used frequently in laboratory diagnosis Major surface antigen but rarely used in laboratory diagnosis Plasma membrane Lipoprotein bilayer w ithout sterols Site of oxidative and transport enzymes Ribosome RNA and protein in 50S and 30S subunits Protein synthesis; site of action of aminoglycosides, erythromycin, tetracyclines, and chloramphenicol Nucleoid DNA Genetic material Mesosome Invagination of plasma membrane Participates in cell division and secretion Periplasm Space betw een plasma membrane and outer membrane Contains many hydrolytic enzymes, including -lactamases Nonessential components Capsule Polysaccharide Protects against phagocytosis Pilus or fimbria Glycoprotein Tw o types: (1) mediates attachment to cell surfaces; (2) sex pilus mediates attachment of tw o bacteria during conjugation Flagellum Protein Motility Spore Keratinlike coat, dipicolinic acid Provides resistance to dehydration, heat, and chemicals Plasmid DNA Contains a variety of genes for antibiotic resistance and toxins Granule Glycogen, lipids, polyphosphates Site of nutrients in cytoplasm Glycocalyx Polysaccharide Mediates adherence to surfaces Except in Bacillus anthracis, in w hich it is a polypeptide of D -glutamic acid Cell Wall The cell w all is the outermost component common to all bacteria (except Mycoplasma species, w hich are bounded by a cell membrane, not a cell w all) Some bacteria have surface features external to the cell w all, such as a capsule, flagella, and pili, w hich are less common components and are discussed below The cell w all is a multilayered structure located external to the cytoplasmic membrane It is composed of an inner layer of peptidoglycan (see Peptidoglycan) and an outer membrane that varies in thickness and chemical composition depending upon the bacterial type (Figure 2–4) The peptidoglycan provides structural support and maintains the characteristic shape of the cell Figure 2–4 / 545 C ell walls of gram-positive and gram-negative bacteria Note that the peptidoglycan in gram-positive bacteria is much thicker than in gram-negative bacteria Note also that only gram-negative bacteria have an outer membrane containing endotoxin (lipopolysaccharide [LPS]) and have a periplasmic space where -lactamases are found Several important gram-positive bacteria, such as staphylococci and streptococci, have teichoic acids (Reproduced with permission from Ingraham JL, Maaløe O, Neidhardt FC Growth of the Bacterial Cell Sinauer Associates; 1983.) CELL WALLS OF GRAM-POSITIVE AND GRAM-NEGATIVE BACTERIA The structure, chemical composition, and thickness of the cell w all differ in gram-positive and gram-negative bacteria (Table –2 and Gram Stain) The peptidoglycan layer is much thicker in gram-positive than in gram-negative bacteria Some gram-positive bacteria also have fibers of teichoic acid, w hich protrude outside the peptidoglycan, w hereas gram-negative bacteria not In contrast, the gram-negative bacteria have a complex outer layer consisting of lipopolysaccharide, lipoprotein, and phospholipid Lying betw een the outer-membrane layer and the cytoplasmic membrane in gram-negative bacteria is the periplasmic space, w hich is the site, in some species, of enzymes called -lactamases that degrade penicillins and other -lactam drugs Table 2–2 Comparison of Cell Walls of Gram-Positive and Gram-Negative Bacteria Component Gram-Positive Cells Gram-Negative Cells Peptidoglycan Thicker; multilayer Thinner; single layer Teichoic acids Yes No Lipopolysaccharide (endotoxin) No Yes The cell w all has several other important properties: In gram-negative bacteria, it contains endotoxin, a lipopolysaccharide (see Lipopolysaccharide and Endotoxins) Its polysaccharides and proteins are antigens that are useful in laboratory identification Its porin proteins play a role in facilitating the passage of small, hydrophilic molecules into the cell Porin proteins in the outer membrane of gram-negative bacteria act as a channel to allow the entry of essential substances such as sugars, amino acids, vitamins, and metals as w ell as many antimicrobial drugs such as penicillins CELL WALLS OF ACID-FAST BACTERIA Mycobacteria, e.g., Mycobacterium tuberculosis, have an unusual cell w all, resulting in their inability to be Gram-stained These bacteria are said to be acid-fast because they resist decolorization w ith acid–alcohol after being stained w ith carbolfuchsin This property is related to the high concentration of lipids, called mycolic acids, in the cell w all of mycobacteria In view of their importance, three components of the cell w all, i.e., peptidoglycan, lipopolysaccharide, and teichoic acid, w ill be discussed in detail PEPTIDOGLY CAN Peptidoglycan is a complex, interw oven netw ork that surrounds the entire cell and is composed of a single covalently linked macromolecule It is found only in bacterial cell w alls It provides rigid support for the cell, is important in maintaining the characteristic shape of the cell, and allow s the cell to w ithstand media of low osmotic pressure, such as w ater A representative segment of the peptidoglycan layer is show n in Figure 2–5 The term "peptidoglycan" is derived from the peptides and the sugars (glycan) that make up the molecule Synonyms for peptidoglycan are murein and mucopeptide 10 / 545 erythromycin, indicating that Legionella and Mycoplasma are unlikely causes See owl's-eye inclusion bodies within the nucleus of infected cells in bronchoalveolar lavage fluid Diagnosis: Cytomegalovirus pneumonia These intranuclear inclusions are typical findings in CMV infections Immunosuppression predisposes to disseminated CMV infections See Cytomegalovirus (CMV) for additional information CASE A 45-year-old w oman complains that her right arm has become increasingly w eak during the past few days This morning, she had a generalized seizure She recently finished a course of cancer chemotherapy MRI of the brain reveals a lesion resembling an abscess Brain biopsy show s gram-positive rods in long filaments Organism is weakly acid-fast Diagnosis: Brain abscess caused by Nocardia asteroides N asteroides initially infects the lung, w here it may or may not cause symptoms in immunocompetent people Dissemination to the brain is common in immunocompromised patients See Nocardia asteroides for additional information CASE A 20-year-old man has a severe headache and vomiting that began yesterday He is now confused On examination, his temperature is 39°C and his neck is stiff Spinal fluid reveals no bacteria on Gram stain, 25 lymphs, normal protein, and normal glucose Culture of the spinal fluid on blood agar show s no bacterial colonies Diagnosis: Viral meningitis, which is most often caused by Coxsackie virus Can isolate the virus from spinal fluid See Coxsackie Viruses for additional information CASE 10 A 60-year-old man w ith a history of tuberculosis now has a cough productive of bloody sputum Chest X-ray reveals a round opaque mass w ithin a cavity in his left upper lobe Culture of the sputum grew an organism w ith septate hyphae that had straight, parallel walls The hyphae exhibited low-angle branching Diagnosis: "Fungus ball" caused by Aspergillus fumigatus Fungal spores are inhaled into the lung, w here they grow w ithin a preexisting cavity caused by infection w ith Mycobacterium tuberculosis See Aspergillus for additional information CASE 11 A 3-month-old girl has w atery, nonbloody diarrhea Stool culture reveals only normal enteric flora Diagnosis: Think rotavirus, the most common cause of diarrhea in infants The ELISA test for rotavirus antigen in the stool is positive, w hich confirms the diagnosis See Rotavirus for additional information CASE 12 A 30-year-old w oman has a painless ulcer on her tongue She is HIV-antibody-positive and has a CD4 count of 25 Her serum is nonreactive in the VDRL test Biopsy of the lesion revealed yeasts within macrophages Diagnosis: Disseminated histoplasmosis caused by Histoplasma capsulatum Patients w ith a low CD4 count have severely reduced cell-mediated immunity, w hich predisposes to disseminated disease caused by this dimorphic fungus A negative VDRL test indicates the ulcer w as not caused by Treponema pallidum See Histoplasma for additional information CASE 13 A 20-year-old man has a sw ollen, red, hot, tender ankle, accompanied by a temperature of 100°F for the past days There is no history of trauma See gram-negative diplococci in joint fluid aspirate Organism is oxidase-positive Diagnosis: Arthritis caused by Neisseria gonorrhoeae, the most common cause of infectious arthritis in sexually active adults Sugar fermentation tests w ere used to identify the organism as N gonorrhoeae See Neisseria gonorrhoeae for additional information CASE 14 A 40-year-old w oman has blurred vision and slurred speech She is afebrile She is famous in her neighborhood for her homecanned vegetables and fruits Diagnosis: Botulism caused by Clostridium botulinum Botulinum toxin causes a descending paralysis that starts w ith the cranial nerves, typically appearing initially as diplopia The toxin is a protease that cleaves the proteins involved in the release of acetylcholine at the neuromuscular junction Treat w ith antiserum immediately Confirm diagnosis with mouse protection test using a sample of food suspected of containing the toxin See Clostridium botulinum for additional information Wound botulism occurs in heroin users (e.g., users of black tar heroin), especially in those w ho "skin pop." Bacterial spores in the heroin germinate in the anaerobic conditions in necrotic skin tissue CASE 15 A neonate w as born w ith a small head (microcephaly), jaundice, and hepatosplenomegaly Urine contained multinucleated giant cells with intranuclear inclusions Diagnosis: Cytomegalovirus infection acquired in utero Cytomegalovirus is the leading cause of congenital abnormalities For fetal infection to occur, the mother must be infected for the first time during pregnancy She therefore w ould have no preexisting antibodies to neutralize the virus prior to its infecting the placenta and the fetus See Cytomegalovirus (CMV) for additional information 531 / 545 CASE 16 A 14-year-old girl has a rapidly spreading, painful, erythematous rash on her leg The rash is w arm and tender, and her temperature is 38°C Gram-positive cocci in chains w ere seen in an aspirate from the lesion Culture of the aspirate on blood agar grew colonies surrounded by clear (beta) hemolysis Grow th of the organism w as inhibited by bacitracin Diagnosis: Cellulitis caused by Streptococcus pyogenes The rapid spread of cellulitis caused by S pyogenes is due to hyaluronidase (spreading factor) that degrades hyaluronic acid in subcutaneous tissue Acute glomerulonephritis (AGN) can follow skin infections caused by S pyogenes AGN is an immunologic disease caused by antigen–antibody complexes See Clinical Findings for additional information CASE 17 A 4-year-old boy w akes up at night because his anal area is itching See worm eggs in "Scotch tape" preparation Diagnosis: Pinw orm infection (enterobiasis) caused by Enterobius vermicularis Pinw orm infection is the most common helminth disease in the United States See Enterobius for additional information CASE 18 A 25-year-old w oman has a painful, inflamed sw ollen hand She w as bitten by a cat about hours ago See small gramnegative rods in the exudate from lesion Diagnosis: Cellulitis caused by Pasteurella multocida Organism is normal flora in cat's mouth See Pasteurella for additional information CASE 19 A 7-year-old girl has bloody diarrhea and fever (temperature, 38°C), but no nausea or vomiting Only lactose-fermenting colonies are seen on EMB agar Diagnosis: Think Campylobacter jejuni or enterohemorrhagic strains of Escherichia coli (E coli O157:H7) If Campylobacter is the cause, see colonies on Campylobacter agar containing curved gram-negative rods, and the colonies on EMB agar are likely to be nonpathogenic E coli If E coli O157:H7 is the cause, the organism in the lactose-fermenting colonies on EMB agar is unable to ferment sorbitol The absence of non–lactose-fermenting colonies indicates that Shigella and Salmonella are not the cause See Campylobacter for additional information and Intestinal Tract Infection for additional information about E coli O157:H7 CASE 20 A 15-year-old girl has had a nonproductive cough and temperature of 100°F for the past days The symptoms came on gradually Lung examination show s few scattered rales Chest X-ray show s patchy infiltrate in left low er lobe but no consolidation Cold agglutinin test is positive Diagnosis: Atypical pneumonia caused by Mycoplasma pneumoniae This organism is the most common cause of atypical pneumonia in teenagers and young adults In the cold agglutinin test, antibodies in the patient's serum agglutinate human red blood cells in the cold (4°C) These antibodies not react w ith Mycoplasma See Mycoplasma pneumoniae for additional information CASE 21 A 45-year-old man sustained a skull fracture in an automobile accident The follow ing day, he noted clear fluid dripping from his nose, but he did not notify the hospital personnel The follow ing day he spiked a fever to 39°C and complained of a severe headache Nuchal rigidity w as found on physical examination Spinal fluid analysis revealed 5200 W BC/ L, 90% of w hich w ere neutrophils Gram stain show ed gram-positive diplococci Diagnosis: Meningitis caused by Streptococcus pneumoniae Patients w ith a fracture of the cribriform plate who leak spinal fluid into the nose are predisposed to meningitis by this organism Pneumococci can colonize the nasal mucosa and enter the subarachnoid space through the fractured cribriform plate See Streptococcus pneumoniae for additional information CASE 22 A 7-year-old girl w as w ell until about w eeks ago, w hen she began complaining of being "tired all the time." On examination, her temperature is 38°C and there is tenderness below the right knee Hemoglobin: 10.2; W BC: 9600 w ith increased neutrophils A sickle cell prep show s a moderate sickling tendency Gram-negative rods grew in the blood culture Diagnosis: Osteomyelitis caused by Salmonella species Sickle cell anemia predisposes to osteomyelitis caused by Salm onella species The abnormally shaped sickle cells are trapped in the small capillaries of the bone and cause microinfarcts These microinfarcts enhance the likelihood of infection by Salmonella See Salmonella for additional information CASE 23 A 3-month-old boy has a persistent cough and severe w heezing for the past days On physical examination, his temperature is 39°C and coarse rhonchi are heard bilaterally Chest X-ray show s interstitial infiltrates bilaterally Diagnosis w as made by ELISA that detected viral antigen in nasal washings Diagnosis: Think pneumonia caused by respiratory syncytial virus, the most common cause of pneumonia and bronchiolitis in infants RSV causes giant cells (syncytia) that can be seen in respiratory secretions and in cell culture See Respiratory Syncytial Virus for additional information CASE 24 532 / 545 A 34-year-old man w as in his usual state of health until last night, w hen he felt feverish, had a shaking chill, and became short of breath at rest T 39°C, BP 110/60, P 104, R 18 Scattered rales w ere heard in both bases A new murmur consistent w ith tricuspid insufficiency w as heard Needle tracks w ere seen on both forearms Gram-positive cocci in clusters grew in blood culture Diagnosis: Acute endocarditis caused by Staphylococcus aureus This organism is the most common cause of acute endocarditis in intravenous drug users The valves on the right side of the heart are often involved See Staphylococcus for additional information CASE 25 A 2-w eek-old infant w as w ell on discharge from the hospital 10 days ago and remained so until last night, w hen he appeared drow sy and flushed His skin felt hot to the touch On physical examination, the infant w as very difficult to arouse, but there w ere no other positive findings His temperature w as 40°C Blood culture grew gram-positive cocci in chains A narrow zone of clear (beta) hemolysis w as seen around the colonies Hippurate hydrolysis test w as positive Diagnosis: Neonatal sepsis caused by Streptococcus agalactiae (group B streptococci) Group B streptococci are the most common cause of neonatal sepsis Think Escherichia coli if gram-negative rods are seen or Listeria monocytogenes if grampositive rods are seen See Clinical Findings for additional information on group B streptococci, Escherichia for additional information on Escherichia coli, and Listeria monocytogenes for additional information CASE 26 A 70-year-old w oman had a hip replacement because of severe degenerative joint disease She did w ell until a year later, w hen a fall resulted in a fracture of the femur and the prosthesis had to be replaced Three w eeks later, bloody fluid began draining from the w ound site The patient w as afebrile and the physical examination w as otherw ise unremarkable Tw o days later, because of increasing drainage, the w ound w as debrided and pus w as obtained Gram stain of the pus w as negative, but an acid-fast stain revealed red rods Diagnosis: Prosthetic joint infection caused by Mycobacterium fortuitum-chelonei complex Think Staphylococcus epidermidis if gram-positive cocci in clusters are seen See Group IV (Rapidly Grow ing Mycobacteria) for additional information on Mycobacterium fortuitum-chelonei complex and Staphylococcus epidermidis & Staphylococcus saprophyticus for additional information on Staphylococcus epidermidis CASE 27 An 80-year-old man complains of a painful rash on his left forehead The rash is vesicular and only on that side He is being treated w ith chemotherapy for leukemia Smear of material from the base of the vesicle reveals multinucleated giant cells with intranuclear inclusions Diagnosis: Herpes zoster (shingles) caused by varicella-zoster virus The rash of zoster follow s the dermatome of the neuron that w as latently infected Herpes simplex type virus can cause a similar picture Can distinguish these viruses using fluorescent antibody assay See Varicella-Zoster Virus (VZV) for additional information CASE 28 A 55-year-old w oman has an inflamed ulcer on her right hand and several tender nodules on the inner aspect of her right arm She is an avid gardener and especially enjoys pruning her roses Biopsy of the lesion reveals budding yeasts Diagnosis: Sporotrichosis caused by Sporothrix schenckii The organism is a mold in the soil and a yeast in the body, i.e., it is dimorphic Infection occurs w hen spores produced by the mold form are introduced into the skin by a penetrating injury See Sporotrichosis for additional information CASE 29 A 15-year-old boy sustained a broken tooth in a fist fight several w eeks ago He now has an inflamed area on the skin over the broken tooth, in the center of w hich is a draining sinus tract Gram stain of the drainage fluid reveals filamentous grampositive rods Diagnosis: Actinomycosis caused by Actinomyces israelii See "sulfur granules" in the sinus tract These granules are particles composed of interw oven filaments of bacteria See Actinomyces israelii for additional information CASE 30 A 24-year-old w oman experienced the sudden onset of high fever, myalgias, vomiting, and diarrhea Her vital signs w ere T 40°C, BP 70/30, P 140, R 30 A sunburn-like rash appeared over most of her body Blood cultures and stool cultures are negative She is recovering from a surgical procedure on her maxillary sinus and the bleeding w as being staunched w ith nasal tampons Gram-positive cocci in clusters w ere seen in blood adherent to the nasal tampon Diagnosis: Toxic shock syndrome caused by Staphylococcus aureus Toxic shock syndrome toxin is a superantigen that stimulates the release of large amounts of cytokines from many helper T cells See Staphylococcus aureus for additional information CASE 31 An 8-year-old girl has a pruritic rash on her chest Lesions are round or oval w ith an inflamed border and central clearing The lesions contain both papules and vesicles See hyphae in KOH prep of scrapings from the lesion Diagnosis: Tinea corporis (ringw orm) caused by one of the dermatophytes, especially species of Microsporum, Trichophyton, or Epidermophyton Dermatophytes utilize keratin as a nutrient source, so lesions are limited to the skin See Dermatophytoses 533 / 545 Epidermophyton Dermatophytes utilize keratin as a nutrient source, so lesions are limited to the skin See Dermatophytoses for additional information CASE 32 A 25-year-old w oman has a papular rash on her trunk, arms, and palms She says the rash does not itch Vaginal examination reveals tw o flat, moist, slightly raised lesions on the labia Material from a labial lesion examined in a darkfield microscope revealed spirochetes Diagnosis: Secondary syphilis caused by Treponema pallidum The rash on the palms coupled w ith the vaginal lesions (condylomata lata) are compatible w ith secondary syphilis Serologic tests, such as the nonspecific test (VDRL) and the specific test (FTA-ABS), were positive See Nonspecific Serologic Tests for additional information CASE 33 A 5-year-old girl complains of an earache for the past days On examination, she has a temperature of 39°C, the right external canal contained dried blood, the drum w as perforated, and a small amount of purulent fluid w as seen Gram stain of the pus revealed gram-positive diplococci Colonies formed green (alpha) hemolysis on blood agar Grow th w as inhibited by optochin Diagnosis: Otitis media caused by Streptococcus pneumoniae Think Haemophilus influenzae if small gram-negative rods are seen These organisms colonize the oropharynx and enter the middle ear via the eustachian tube See Streptococcus pneumoniae for additional information on Streptococcus pneumoniae and Haemophilus for additional information on Haemophilus influenzae CASE 34 A 25-year-old w oman w as w ell until the sudden onset of high fever (temperature, 40°C) accompanied by several purple skin lesions (ecchymoses, purpura) The lesions are scattered over the body, are irregularly shaped, and are not raised Her blood pressure is 60/10 and her pulse rate is 140 Blood culture grew gram-negative diplococci Diagnosis: Meningococcemia caused by Neisseria meningitidis The endotoxin (lipopolysaccharide, or LPS) of the organism triggers release of interleukin-1, tumor necrosis factor, and nitric oxide from macrophages These cause the high fever and low blood pressure The purpuric lesions are a manifestation of disseminated intravascular coagulation (DIC) Endotoxin activates the coagulation cascade, causing DIC Lipid A is the toxic part of LPS See Neisseria for additional information CASE 35 A 40-year-old w oman w as w ell until days ago, w hen she experienced the sudden onset of fever, shaking chills, and profuse sw eating Today, she also complains of headache and abdominal pain but no nausea, vomiting, or diarrhea She does not have a stiff neck, rash, or altered mental status Travel history reveals she returned from an extended trip to several countries in Central Africa w eek ago Blood smear reveals ring-shaped trophozoites within red blood cells Diagnosis: Malaria caused by Plasmodium species If banana-shaped gametocytes seen in the blood smear, think Plasmodium falciparum P falciparum is the species that causes the life-threatening complications of malaria, such as cerebral malaria The fever and chills experienced by the patient coincide w ith the release of merozoites from infected red blood cells and occur in either a tertian or quartan pattern See Plasmodium for additional information CASE 36 A 35-year-old man is seen in the emergency room complaining of severe headache and vomiting that began last night His temperature is 40°C W hile in the ER, he is increasingly combative and has a grand mal seizure He is "foaming at the mouth" and cannot drink any liquids Analysis of his spinal fluid reveals no abnormality, and no organisms are seen in the Gram stain Tw o days later, despite supportive measures, he died Pathologic examination of the brain revealed eosinophilic inclusion bodies in the cytoplasm of neurons Diagnosis: Rabies (an encephalitis) caused by rabies virus The inclusions are Negri bodies Diagnosis can be confirmed by using fluorescent antibody assays The patient w as a farm w orker w ho w as bitten by a bat about a month prior to the onset of symptoms Note the long incubation period, w hich can be as long as months People bitten by a bat (or any w ild animal) should receive rabies immunization consisting of the inactivated vaccine plus rabies immune globulins (passive–active immunization) See Rabies Virus for additional information CASE 37 A 70-year-old man w as admitted to the hospital after suffering extensive third-degree burns Three days later, he spiked a fever, and there w as pus on the dressing that had a blue-green color Gram stain of the pus revealed gram-negative rods Diagnosis: Wound (burn) infection caused by Pseudomonas aeruginosa The blue-green color is caused by pyocyanin, a pigment produced by the organism See Pseudomonas for additional information CASE 38 A 65-year-old w oman reports that she has had several episodes of confusion and memory loss during the past few w eeks On examination, she is afebrile but has a staggering gait and myoclonus can be elicited Over the next several months, her condition deteriorates and death ensues On autopsy, microscopic examination of the brain reveals many vacuoles but no viral inclusion bodies Diagnosis: Creutzfeldt-Jakob disease caused by prions CJD is a spongiform encephalopathy The vacuoles give the brain a sponge-like appearance See Creutzfeldt-Jakob Disease for additional information 534 / 545 CASE 39 A 20-year-old man complains of several episodes of blood in his urine He has no dysuria or urethral discharge He is not sexually active He is a college student but w as born and raised in Egypt Physical examination reveals no penile lesions Urinalysis show s many red cells, no w hite cells, and several large eggs with terminal spines Diagnosis: Schistosomiasis caused by Schistosoma haematobium Schistosome eggs in venules of the bladder damage the bladder epithelium and cause bleeding The eggs are excreted in the urine See Schistosoma for additional information CASE 40 A 35-year-old man complains of night sw eats, chills, and fatigue at varying intervals during the past months These episodes began w hile he w as traveling in Latin America W hen questioned, he says that cheeses, especially the unpasteurized varieties, are some of his favorite foods On examination, his temperature is 39°C, and his liver and spleen are palpable His hematocrit is 30% and his w hite blood count is 5000 Blood culture grew small gram-negative rods Diagnosis: Brucellosis caused by Brucella species Domestic animals such as cow s and goats are the main reservoir for Brucella, and it is often transmitted in unpasteurized dairy products This patient could also have typhoid fever caused by Salmonella typhi, but S ty phi is only a human pathogen, i.e., there is no animal reservoir See Brucella for additional information on Brucella species and Salmonella for additional information on Salmonella typhi CASE 41 A 6-year-old girl has a rash on her face that appeared yesterday The rash is erythematous and located over the malar eminences bilaterally The rash is macular; there are no papules, vesicles, or pustules A few days prior to the appearance of the rash, she had a runny nose and anorexia Diagnosis: Slapped cheek syndrome caused by parvovirus B19 This virus also causes aplastic anemia because it preferentially infects and kills erythroblasts It also infects the fetus, causing hydrops fetalis, and causes an immune complex–mediated arthritis, especially in adult w omen See Parvoviruses for additional information CASE 42 A 20-year-old man fell off his motorcycle and suffered a compound fracture of the femur The fracture w as surgically reduced and the w ound debrided Forty-eight hours later, he spiked a fever (temperature, 40°C) and the w ound area became necrotic Crepitus w as felt, and a foul-smelling odor w as perceived originating from the w ound Marked anemia and a w hite blood count of 22,800 w ere found Gram stain of the exudate show ed large gram-positive rods Colonies grew on blood agar incubated anaerobically but not aerobically Diagnosis: Gas gangrene (myonecrosis) caused by Clostridium perfringens The main virulence factor produced by this organism is an exotoxin that is a lecithinase It causes necrosis of tissue and lysis of red blood cells (causing hemolytic anemia) The spores of the organism are in the soil and enter at the w ound site A foul-smelling exudate is characteristic of infections caused by anaerobic bacteria See Clostridium perfringens for additional information CASE 43 A 30-year-old w oman complains of a burning feeling in her mouth and pain on sw allow ing Sexual history reveals she is a commercial sex w orker and has had unprotected vaginal, oral, and anal intercourse w ith multiple partners On examination, w hitish lesions are seen on the tongue, palate, and pharynx No vesicles are seen The test for HIV antibody is positive and her CD4 count is 65 Gram stain of material from the lesions reveals budding yeasts and pseudohyphae Diagnosis: Thrush caused by Candida albicans This organism forms pseudohyphae w hen it invades tissue The absence of vesicles indicates that her symptoms are not caused by herpes simplex virus type See Candida for additional information CASE 44 You're a physician at a refugee camp in sub-Saharan Africa, w hen an outbreak of diarrhea occurs Massive amounts of w atery stool, w ithout blood, are produced by the patients Curved gram-negative rods are seen in a Gram stain of the stool Diagnosis: Cholera caused by Vibrio cholerae There are three genera of curved gram-negative rods: Vibrio, Cam py lobacter, and Helicobacter Vibrio cholerae causes w atery, nonbloody diarrhea, w hereas Campylobacter jejuni typically causes bloody diarrhea Helicobacter pylori causes gastritis and peptic ulcer, not diarrhea Enterotoxigenic Escherichia coli causes w atery diarrhea by producing an exotoxin that has the same mode of action as does the exotoxin produced by V cholerae How ever, E coli is a straight gram-negative rod, not a curved one If an outbreak of bloody diarrhea had occurred in the refugee camp, then Shigella dysenteriae w ould be the most likely cause See the follow ing sections for additional information: Vibrio, Campylobacter, Helicobacter, Escherichia, and Shigella CASE 45 A 40-year-old man w ith low -grade fever and night sw eats for the past w eeks now has increasing fatigue and shortness of breath He says he has difficulty climbing the one flight of stairs to his apartment Pertinent past history includes rheumatic fever w hen he w as 15 years old and the extraction of tw o w isdom teeth about w eeks before his symptoms began No chemoprophylaxis w as given at the time of the extractions There is no history of intravenous drug use His temperature is 38.5°C, and a loud holosystolic murmur can be heard over the precordium His spleen is palpable He is anemic and his w hite blood count is 13,500 Blood cultures grow gram-positive cocci in chains that produce green (alpha) hemolysis on blood agar Grow th is not inhibited by optochin Diagnosis: Subacute bacterial endocarditis caused by one of the viridans group streptococci, such as Streptococcus sanguis The laboratory findings are also compatible w ith Enterococcus faecalis, but the history of dental surgery makes the viridans 535 / 545 The laboratory findings are also compatible w ith Enterococcus faecalis, but the history of dental surgery makes the viridans group streptococci more likely to be the cause Endocarditis caused by E faecalis is associated w ith GI or GU tract surgery See Diseases for additional information on both viridans group streptococci and E faecalis CASE 46 A 60-year-old w oman is asymptomatic but has a lung nodule seen on chest X-ray Pertinent past history includes her cigarette smoking (2 packs per day for 40 years) and her occupation as an archaeologist, digging primarily in Arizona and New Mexico Because of concern that the nodule may be malignant, it w as surgically removed Pathologic examination revealed large (25 ) round structures with thick walls and many round spores inside No malignant cells w ere seen Diagnosis: Coccidioidomycosis caused by Coccidioides immitis These structures are spherules, w hich are pathognomonic for this disease The mold form of the organism is found in the soil of the Southw estern United States, and the organism is acquired by inhalation of arthrospores produced by the mold The inhaled arthrospores form spherules in the lung C immitis is dimorphic and forms spherules at 37°C See Coccidioides for additional information CASE 47 A 20-year-old w oman in her 30th w eek of pregnancy had an ultrasound examination that revealed a grow th-retarded fetus w ith a large head (indicating hydrocephalus) and calcifications w ithin the brain Umbilical blood w as cultured and crescentshaped trophozoites w ere grow n Diagnosis: Toxoplasmosis caused by Toxoplasma gondii Detection of IgM antibody in the Sabin-Feldman dye test can also be used to make a diagnosis The main reservoir is domestic cats Domestic farm animals, such as cattle, acquire the organism by accidentally eating cat feces Pregnant w omen should not be exposed to cat litter or eat undercooked meat See Toxoplasma for additional information CASE 48 A 10-day-old neonate has several vesicles on the scalp and around the eyes The child is otherw ise w ell, afebrile and feeding normally A Giemsa-stained smear of material from the base of a vesicle revealed multinucleated giant cells with intranuclear inclusions Diagnosis: Neonatal infection caused by herpes simplex virus type Infection is acquired during passage through the birth canal Life-threatening encephalitis and disseminated infection of the neonate also occur See Herpes Simplex Viruses (HSV) for additional information CASE 49 A 40-year-old w oman has just had a grand mal seizure There is a history of headaches for the past w eek and one episode of vertigo but no previous seizures She is afebrile She is a native of Honduras but has lived in the United States for the past years MRI reveals a mass in the parietal lobe Surgical removal of the mass reveals a larva within a cystlike sac Diagnosis: Cysticercosis caused by the larva of Taenia solium Infection is acquired by ingesting the tape-w orm eggs, not by ingesting undercooked pork This clinical picture can also be caused by a brain abscess, a granuloma such as a tuberculoma, or a brain tumor See Taenia solium for additional information CASE 50 A 1-w eek-old neonate has a yellow ish exudate in the corners of both eyes The child is otherw ise w ell, afebrile and feeding normally Gram stain of the exudate reveals no gram-negative diplococci A Giemsa-stained smear of the exudate reveals a large cytoplasmic inclusion Diagnosis: Conjunctivitis caused by Chlamydia trachomatis Confirm the diagnosis w ith direct fluorescent antibody test Infection is acquired during passage through the birth canal The inclusion contains large numbers of the intracellular replicating forms called reticulate bodies See Diseases for additional information C opyright © The McGraw-Hill C ompanies All rights reserved Privacy Notice Any use is subject to the Terms of Use and Notice 536 / 545 Print Close W indow Note: Large im ages and tables on this page m ay necessitate printing in landscape m ode Copyright © The McGraw-Hill Companies A ll rights reserved Review of Medical Microbiology and Immunology > Part XI Pearls for the USMLE > PEARLS FOR T HE USMLE: INT RODUCT ION Many questions on the USMLE can be answ ered by know ing the meaning of the epidemiological information provided in the case description In order to this, the student should know the reservoir of the organism, its mode of transmission, and the meaning of factors such as travel, occupation, and exposure to pets, farm animals, or w ild animals Know ledge of the microbes that typically cause disease in individuals w ith specific immunodeficiencies w ill also be helpful In addition to being useful for the USMLE, this information w ill prove valuable to make the diagnosis of infectious diseases on the w ards and in your clinical practice The "Pearls" are presented in tables entitled: Table XI–1 Farm Animals and Household Pets as Reservoirs of Medically Important Organisms Table XI–2 W ild Animals as Reservoirs of Medically Important Organisms Table XI–3 Insects as Vectors of Medically Important Organisms Table XI–4 Environmental Sources of Medically Important Organisms Table XI–5 Main Geographical Location of Medically Important Organisms Table XI–6 Occupations and Avocations That Increase Exposure to Medically Important Organisms Table XI–7 Hospital-Related Events That Predispose to Infection by Medically Important Organisms Table XI–8 Organisms That Commonly Cause Disease in Patients w ith Immunodeficiencies or Reduced Host Defenses Table XI–9 Important Factors That Predispose to Infections by Specific Organisms Table XI–10 Maternal Infections That Pose Significant Risk to the Fetus or Neonate Table XI–11 Important Skin Lesions Caused by Microorganisms Table XI–1 Farm Animals and Household Pets as Reservoirs of Medically Important Organisms Animal Mode of Transmission Important Organisms Disease Cattle/cow s Ingestion of meat 1 Escherichia coli O157 Enterocolitis and hemolytic uremic syndrome Salmonella enterica Enterocolitis Prions Variant CJD Taenia saginata Taeniasis (intestinal tapew orm) Toxoplasma gondii Toxoplasmosis Ingestion of milk products Listeria monocytogenes Neonatal sepsis Brucella species Brucellosis Mycobacterium bovis Intestinal tuberculosis Contact w ith animal hides Bacillus anthracis Anthrax Sheep Inhalation of amniotic fluid Coxiella burnetii Q fever Goats Ingestion of milk products Brucella species Brucellosis Pigs Ingestion of meat 1 Taenia solium Taeniasis (intestinal tapew orm)3 Trichinella spiralis Trichinosis Salmonella enterica Enterocolitis Campylobacter jejuni Enterocolitis Poultry (chickens; turkeys) Ingestion of meat or eggs 537 / 545 Dogs Cats Ingestion of dog feces Echinococcus granulosus Echinococcosis Toxocara canis Visceral larva migrans Ingestion of dog urine Leptospira interrogans Leptospirosis Dog bite Rabies virus Rabies Ingestion of cat feces Toxoplasma gondii Toxoplasmosis Cat bite/scratch Pasteurella multocida Cellulitis Bartonella henselae Cat-scratch fever; bacillary angiomatosis Rabies virus Rabies Raw or undercooked Unpasteurized Ingestion of eggs in human feces, not ingestion of pork, results in cysticercosis Table XI–2 Wild Animals as Reservoirs of Medically Important Organisms Animal Mode of Transmission Important Organisms Disease Rats Flea bite Yersinia pestis Plague Ingestion of urine Leptospira interrogans Leptospirosis Tick bite Borrelia burgdorferi Lyme disease Inhale aerosol of droppings Hantavirus Hantavirus Mice Pulmonary syndrome Bats, skunks, raccoons, and foxes Bite Rabies virus Rabies Rabbits Contact Frandsella tularensis Tularemia Civet cats, bats Inhale aerosol Coronavirus—SARS Pneumonia Monkeys Mosquito bite Yellow fever virus Yellow fever Psittacine birds (e.g., parrots) Inhale aerosol Chlamydia psittaci Psittacosis Chickens Inhale aerosol Influenzavirus Influenza Pigeons Inhale aerosol Cryptococcus neoformans Meningitis, pneumonia Starlings Inhale aerosol Histoplasma capsulatum Histoplasmosis Sparrow s Mosquito bite Encephalitis viruses (e.g., West Nile virus) Encephalitis Snakes, turtles Fecal-oral Salmonella enterica Enterocolitis Fish Ingestion of fish Anisakis simplex Anisakiasis Diphyllobothrium latum Diphyllobothriasis Birds Raw or undercooked Table XI–3 Insects as Vectors of Medically Important Organisms Insects Important Organisms Reservoir Disease 538 / 545 Ticks Ixodes (deer tick) Borrelia burgdorferi Mice Lyme disease Babesia microti Mice Babesiosis Rickettsia rickettsii Rodents, dogs Rocky Mountain spotted fever Ehrlichia chaffeensis Dogs Ehrlichiosis Rickettsia prowazekii Humans Typhus Anopheles Plasmodium falciparum, P vivax, P ovale, P malariae Humans Malaria Aedes Yellow fever virus Humans and monkeys Yellow fever Aedes Dengue virus Humans Dengue Culex Encephalitis viruses, such as West Nile virus Birds Encephalitis Anopheles and Culex Wuchereria bancrofti Humans Filariasis, especially elephantiasis Yersinia pestis Rats Plague Sandfly Leishmania donovani Various animals Leishmaniasis Tse-tse fly Trypanosoma brucei Humans and various animals Sleeping sickness Blackfly Onchocerca volvulus Humans Onchocerciasis Trypanosoma cruzi Various animals Chagas' disease Dermacentor (dog tick) Lice Mosquitos Fleas Rat flea Flies Bugs Reduviid bug Table XI–4 Environmental Sources of Medically Important Organisms Environmental Source Important Organisms Mode of Transmission Disease Water Legionella pneumophila Inhale aerosol Pneumonia Pseudomonas aeruginosa Inhale aerosol or direct contact Pneumonia, burn, and w ound infections Mycobacterium marinum Skin abrasion Sw imming pool granuloma Vibrio vulnificus Skin abrasion Cellulitis Schistosoma mansoni, S hematobium Cercariae enter skin Schistosomiasis Naegleria fowleri Ameba enter nose w hile sw imming Meningoencephalitis Clostridium tetani Spores in soil enter w ound Tetanus Clostridium botulinum Spores in soil contaminate food that is improperly canned Botulism Clostridium perfringens Spores in soil enter w ound Gas gangrene Bacillus anthracis Spores in soil enter w ound Anthrax Atypical mycobacteria (e.g., M avium-intracellulare) Inhale aerosol Tuberculosis-like disease Soil 539 / 545 Nocardia asteroides Inhale aerosol Nocardiosis Cryptococcus neoformans Inhale yeast in aerosol associated w ith pigeons Meningitis, pneumonia Histoplasma capsulatum Inhale spores in aerosol associated w ith Histoplasmosis starlings Coccidioides immitis Inhale spores in aerosol of soil dust Coccidioidomycosis 10 Sporothrix schenckii Spores in soil enter w ound Sporotrichosis 11 Ancylostoma duodenale and Necator americanus Filariform larvae enter skin Hookw orm, especially anemia 12 Strongyloides stercoralis Filariform larvae enter skin Strongyloidiasis 13 Ancylostoma caninum Filariform larvae enter skin Cutaneous larva migrans Table XI–5 Main Geographical Location of Medically Important Organisms Main Geographical Location Important Organism Disease South central states (e.g., North Carolina and Virginia) Rickettsia rickettsii Rocky Mountain spotted fever Northeastern states (e.g., Connecticut, New York, and New Jersey) Borrelia burgdorferi Lyme disease Histoplasma capsulation Histoplasmosis Within the United States Midw estern states in the Ohio and Mississippi River valleys (e.g., Missouri and Illinois) Southw estern states (e.g., California and Arizona) Coccidioides immitis Coccidioidomycosis Outside the United States Tropical areas of Africa, Asia, and South America Plasmodium species Malaria Central America Trypanosoma cruzi Chagas' disease Caribbean Islands and Africa Dengue virus Dengue fever West Africa Ebola virus Ebola hemorrhagic fever Tropical areas of Africa and South America Yellow fever virus Yellow fever Sub-Saharan Africa Neisseria meningitidis Meningococcal meningitis Central Africa Trypanosoma brucei African sleeping sickness Middle East, Africa, and India Leishmania donovani Visceral leishmaniasis (kalaazar) Middle East, Africa, and India Leishmania tropica Cutaneous leishmaniasis 10 Central and South America Leishmania braziliensis Mucocutaneous Leishmaniasis Table XI–6 Occupations and Avocations That Increase Exposure to Medically Important Organisms Occupation/Avocation Predisposing Factor Important Organism Disease Hiking/camping Tick exposure Borrelia burgdorferi Lyme disease Rancher/farm w orker Skin w ound contaminated w ith soil Bacillus anthracis Anthrax 540 / 545 Sew er w orker Exposure to rat urine Leptospira interrogans Leptospirosis Cave explorer (spelunker) in bat-infested caves Exposure to aerosol of bat saliva Rabies virus Rabies Cave explorer (spelunker) or construction w orker Exposure to aerosol of bat guano Histoplasma capsulatum Histoplasmosis Archaeologist or construction w orker digging in soil Exposure to soil dust containing spores Coccidioides immitis Coccidioidomycosis Pigeon fancier Exposure to aerosol of bird guano Cryptococcus neoformans Cryptococcosis Bear hunter in Alaska Ingestion of bear meat Trichinella spiralis Trichinosis Aquarium personnel/sw imming pool Abrasion of skin Mycobacterium marinum "Sw imming pool granuloma" Table XI–7 Hospital-Related Events That Predispose to Infection by Medically Important Organisms Hospital-Related Event Important Organism Disease Surgery Staphylococcus aureus Wound infection Urinary catheter Escherichia coli primarily, but also other enteric gram-negative rods (e.g., Proteus, Serratia, and Pseudomonas) Urinary tract infection Enterococcus faecalis Urinary tract infection Staphylococcus epidermidis Candida albicans Catheter-related infection, bacteremia Intravenous catheter Prosthetic device (e.g., hip Staphylococcus epidermidis or heart valve) Osteomyelitis or endocarditis Mycobacterium fortuitum-cheloni Osteomyelitis Respiratory therapy Pseudomonas aeruginosa Pneumonia Burn therapy Pseudomonas aeruginosa Wound infection Intracerebral electrodes Prion Creutzfeldt-Jakob disease Needlestick HBV, HCV Hepatitis B or C HIV AIDS Respiratory syncytial virus Bronchiolitis or pneumonia Premature nursery Table XI–8 Organisms That Commonly Cause Disease in Patients with Immunodeficiencies or Reduced Host Defenses Immunodeficiency or Reduced Host Defense Organisms Reduced antibodies (e.g., agammaglobulinemia and IgA deficiency) Encapsulated bacteria (e.g., Streptococcus pneumoniae, Haemophilus influenzae type b) Reduced phagocytosis (e.g., chronic granulomatous disease, cancer chemotherapy [neutropenia]) Staphylococcus aureus, Pseudomonas aeruginosa, Aspergillus fumigatus Reduced complement C3b Streptococcus pneumoniae, Haemophilus influenzae type b, Staphylococcus aureus C678&9 (membrane attack complex) Neisseria meningitidis Reduced cell-mediated immunity 541 / 545 Thymic aplasia (DiGeorge's syndrome) Candida albicans, Pneumocystis carinii HIV infection (AIDS), corticosteroids Intracellular bacteria (e.g., Mycobacterium tuberculosis, MAI,1 Listeria, Salmonella) Opportunistic fungi (e.g., Candida, Cryptococcus) Herpesviruses (e.g., herpes simplex virus, varicella-zoster virus, cytomegalovirus) Protozoa (e.g., Toxoplasma, Cryptosporidium) Pneumocystis Disrupted epithelial surface (e.g., burns) Pseudomonas aeruginosa Splenectomy Streptococcus pneumoniae Diabetes mellitus Staphylococcus aureus, Mucor species MAI, Mycobacterium avium-intracellulare complex Table XI–9 Important Factors That Predispose to Infections by Specific Organisms Predisposing Factor Organism Disease Pathogenetic Mechanism Cystic fibrosis Pseudomonas aeruginosa Pneumonia Tenacious mucus traps bacteria in airw ays Sickle cell anemia Salmonella enterica Osteomyelitis Abnormally shaped red cells block blood vessels in bone and trap bacteria Streptococcus pneumoniae Sepsis Abnormally shaped red cells block blood vessels in spleen causing infarction of spleen Intravenous drug use Staphylococcus aureus Right-sided endocarditis Skin flora enter venous blood at site of needle Antibiotic use Clostridium difficile Pseudomembranous Antibiotics suppress enteric normal flora allow ing colitis C difficile to grow Aortic aneurysm Salmonella enterica1 Vascular graft infection Uncertain Tampon use (either vaginal or nasal tampon) Staphylococcus aureus Toxic shock syndrome Tampon blocks flow of blood allow ing S aureus to grow and produce toxin Dental surgery Viridans group streptococci Endocarditis These bacteria are normal flora in the mouth and enter the blood at the site of the surgical w ound Motorcycle accident Clostridium perfringens Gas gangrene (myonecrosis) Spores in soil enter w ound site Contact lenses Pseudomonas aeruginosa, Acanthamoeba castellani Keratitis Abrasions caused by lenses provide entry site for organisms Especially S enterica serotype cholera-suis and serotype Dublin Table XI–10 Maternal Infections That Pose Significant Risk to the Fetus or Neonate Microbe Transplacental or Perinatal Transmission to Fetus Comment Cytomegalovirus Transplacental The leading cause of congenital abnormalities Parvovirus B-19 Transplacental Important cause of congenital abnormalities, including hydrops fetalis Rubella virus Transplacental Vaccine has greatly reduced the incidence of fetal infection A Virus 542 / 545 infection Human immunodeficiency virus Perinatal Most are perinatal but transplacental and via breast milk also occurs Hepatitis B virus Perinatal Neonatal HBV infection greatly increases the risk of chronic carrier state Hepatitis C virus Perinatal Neonatal HCV infection greatly increases the risk of chronic carrier state Herpes simplex-2 virus Perinatal Important cause of encephalitis Treponema pallidum Transplacental Causes congenital syphilis Neisseria gonorrhoeae Perinatal Important cause of conjunctivitis (ophthalmia neonatorum) Chlamydia trachomatis Perinatal Important cause of conjunctivitis and pneumonia Perinatal Important cause of meningitis and sepsis Escherichia coli Perinatal Important cause of meningitis and sepsis Listeria monocytogenes Perinatal Important cause of meningitis and sepsis Perinatal Causes thrush of the oropharynx Transplacental Important cause of congenital abnormalities, especially of eye and brain B Bacteria Streptococcus agalactiae (group B streptococcus) C Y east Candida albicans D Protozoan Toxoplasma gondii Table XI–11 Important Skin Lesions Caused by Microorganisms Name or Type of Lesion Causative Organism Description of Lesion Comment Bacillus anthracis Crust over a necrotic ulcer Caused by lethal toxin of B anthracis Carbuncle Staphylococcus aureus Group of furuncles (see below ), often on neck Associated w ith poor personal hygiene Cellulitis Streptococcus pyogenes Red, hot, tender, rapidly spreading, irregular shape Hyaluronidase is "spreading factor" Treponema pallidum Painless, moist, shallow ulcer Darkfield microscopy show s motile spirochetes A Single or localized lesions Black eschar of anthrax Chancre of primary syphilis Cutaneous larva Ancylostoma caninum migrans Pruritic track, often on foot Larva of dog hookw orm migrates in skin Ecthyma gangrenosum Most often Pseudomonas aeruginosa Necrotic ulcer w ith black eschar Neutropenia predisposes Streptococcus pyogenes Raised, red, tender, w ith defined border Rapid progression (minutes to hours); diabetes predisposes Erythema chronicum migrans (ECM) of Lyme disease Borrelia burgdorferi Expanding erythematous Lesion is at site of tick bite Furuncle (boil, folliculitis) A Staphylococcus aureus Erysipelas macule Small pustule at hair follicle A Contains neutrophils and Gram-positive cocci 543 / 545 B Pseudomonas aeruginosa Impetigo Papilloma (Warts) B Causes "hot tub" folliculitis Streptococcus pyogenes and Staphylococcus aureus Vesicles w ith honey-colored Str pyogenes skin infections predispose to acute glomerulonephritis crust Human papilloma virus Raised, dry, non-inflamed papules Benign tumors except HPV 16 and 18 cause carcinoma of cervix Ringw orm Trichophyton, Oval, inflamed, pruritic Epidermophyton, Microsporum border w ith central clearing See hyphae in KOH prep Scabies Sarcoptes scabiei Pruritic track or papule Sar scabiei is called the "itch mite" Parvovirus B19 Erythematous, macular, nontender rash on cheeks Slapped cheeks syndrome Zoster (Shingles) Varicella-zoster virus Painful, vesicles along sensory nerve Reactivation of latent VZV infection B Multiple or disseminated lesions Disseminated gonococcal infection (DGI) Neisseria gonorrhoeae Scattered pustules and inflamed tendons, esp of w rists and fingers (tenosynovitis) Erythema nodosum Systemic fungi, e.g., Coccidioides and Mycobacteria, e.g., M tuberculosis and M leprae Erythematous, tender Immunologic response to circulating nodules on skin over tibia or antigen; no organisms in lesion ulna Hand, foot, & mouth disease Coxsackie virus Vesicles in those locations Measles virus Maculopapular splotchy See Koplik's spots on buccal mucosa; rash (morbilliform) rash, especially caused by cytotoxic T cell attack on viruson head and trunk infected cells Measles Petechial hemorrhage Rocky Mountain Many bacteria, (e.g., Neisseria Small area of bleeding into meningitidis and viruses, e.g., the skin Ebola virus) A sign of disseminated intravascular coagulation (DIC) that occurs in sepsis; can enlarge to form purpuric (ecchymotic) lesions Rickettsia rickettsiae Petechial hemorrhages Rickettsia infect and kill vascular endothelium including on palms and soles resulting in hemorrhage into skin Rubella virus Maculopapular, nonconfluent Milder disease than measles rash on face and trunk Staphylococcus aureus Desquamation over large area of body Streptococcus pyogenes Diffuse, macular, red (scarlet) Caused by strains of Str pyogenes that rash, also straw berry tongue produces erythrogenic toxin w hich is a and circumoral pallor superantigen Secondary syphilis Treponema pallidum Maculopapular rash on trunk, palms, and soles Splinter hemorrhage Viridans streptococci, Sta aureus and other causes of endocarditis Linear, black "splinters" under nails Sign of emboli from vegetation on heart valve Toxic shock syndrome Sta aureus Macular "sunburn-like" rash that desquamates later Toxic shock syndrome toxin (TSST) is a superantigen Varicella (chickenpox) Varicella-zoster virus (VZV) Pruritic vesicles on face and trunk spotted fever Rubella Scalded skin syndrome Scarlet fever Protease that cleaves desmoglein causes desquamation Description of certain important skin lesions: Macule is a flat, erythematous lesion Papule is a raised, erythematous lesion w ith no visible fluid inside; resembles a mosquito bite Vesicle is a raised, erythematous lesion w ith yellow ish fluid (resembling plasma) inside; approximately the same size as a papule Pustule is a raised, erythematous lesion w ith cloudy fluid (pus) 544 / 545 plasma) inside; approximately the same size as a papule Pustule is a raised, erythematous lesion w ith cloudy fluid (pus) inside; typically larger than a papule or vesicle C opyright © The McGraw-Hill C ompanies All rights reserved Privacy Notice Any use is subject to the Terms of Use and Notice 545 / 545 ... Companies A ll rights reserved Review of Medical Microbiology and Immunology > Chapter Classification of Medically Im portant Bacteria > CLASSIFICAT ION OF MEDICALLY IMPORT ANT BACT ERIA: INT RODUCT... determined by the orientation and degree of attachment of the bacteria at the time of cell division The arrangement of rods and spirochetes is medically less important and w ill not be described... name of the w ell-know n bacteria Escherichia coli, Escherichia is the genus and coli is the species name Similarly, the name of the yeast Candida albicans consists of Candida as the genus and
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