Nature and Properties of Micro-organisms Laura JV Piddock Smallest to largest…  Prions  Viruses  Bacteria  Fungi Prions  Infectious protein  No DNA or RNA  Normal cellular form of protein vs. pathological form Pathological form found in neural tissue and tonsils PrP-C & PrP-Sc Pathology  Spongiform encephalopathy: transmissible, familial  Transmission: oral, operative (neural tissue, dura, corneas), ??? blood  Resistance to disinfectants  Formaldehyde increases infectivity Viruses  DNA or RNA  Shell of protein (capsid) surrounding nucleic acid  Classification on basis of nucleic acid  DNA viruses: eg Herpes simplex virus (HSV)  RNA viruses: eg influenza virus DNA viruses: herpes simplex virus (HSV) RNA viruses: Influenza Viruses  Obligate intracellular parasites  Use host cell for nucleic acid and protein synthesis  Cell attachment: target for blocking antibody vaccines  Intracellular replication: target for antiviral drugs  n.b. retroviruses (RNA) e.g. HIV RNA  DNA Viral effects on host cells  Degeneration (cytopathic effect): CMV  Cell lysis  Cell fusion, syncytia formation: RSV  Cell proliferation  Transformation: malignancy (parvoviruses)  Latent infection - no sign of infection until reactivation  ‘cold sores’ (HSV)  chickenpox  shingles (VZV) CMV hepatitis owl eye effect inclusion body [...]... conjugation (transfer of plasmid DNA) Important bacterial products 1: extracellular polysaccharide  CAPSULE condensed, well defined layer closely surrounding the cell contributes to invasiveness of pathogenic bacteria by reducing opsonisation and protecting from phagocytosis  E.g Streptococcus pneumoniae in RTI  vaccination: pneumococcal; meningococcal A and C  GLYCOCALYX loose meshwork of fibrils extending... Gram positives:   synthesis is target for penicillins, cephalosporins and vancomycin lipoteichoic acid, septic shock Beta-lactamases    hydrolyse penicillins and cephalosporins secreted by Gram positive bacteria Within periplasm of Gram negative bacteria Important cell wall components 2 LPS, Endotoxin  Firmly bound to cell and only released upon lysis Only Lipid A is toxic Polysaccharide is a...Varicella zoster virus (VZV) VZV: Chickenpox VZV: Shingles Re-activation of latent infection Suppression of cell mediated immunity Bacteria  Unicellular,  DNA and RNA  Binary  No prokaryotes fission mitochondria  Rigid cell wall containing peptidoglycan Eubacteria  Classified according to:     Gram stain reaction... be removed but is rapidly replaced  Involved in motility and impart spinning movement and usually requires proton motive force  Chemotaxis: flagella move bacteria towards or away from chemical attractant/repellent e.g Vibrio cholerae Flagellae Important bacterial cell components 3: Pili (Fimbrae)  Found on Gram negative bacteria, shorter and finer than flagella  Two classes:  ordinary pili ‘colonisation... obligate intracellular parasite  needs host ATP Chlamydia trachomatis Important bacterial cell components 1: (endo)spores usually Bacillus spp and Clostridium e.g Clostridium tetani (tetanus) spore is a resting cell, highly resistant to desiccation, heat and chemical agents produced in response to environmental conditions e.g nutritional depletion, usually reduction in nitrogen or carbon sources... Shape   coccus - round (chains? clusters?) bacillus - rod Wound swab: S aureus Neisseria gonorrhoeae Gram stained urethral discharge The image shows many polymorphonuclear leukocytes (PMNs) and gram-negative extra- and intra-cellular diplococci (1,000X oil) Pneumococci in sputum Other important bacteria  Strict anaerobes: e.g Bacteroides fragilis  metronidazole sensitive  ‘Higher bacteria’ e.g Mycobacterium... specificity conferred by the terminal repeat units, and many types possible, e.g Salmonella >1000    Fungi  Eukaryotes  Rigid chitinous cell walls  Antifungal drugs interfere with cell wall synthesis  Classified morphologically:  moulds  eg Penicillium, Aspergillus  yeasts  - filamentous, spore-forming - unicellular, budding reproduction eg Candida, Cryptococcus Moulds Yeasts ... vaccination: pneumococcal; meningococcal A and C  GLYCOCALYX loose meshwork of fibrils extending outward from the cell plays a major role in bacterial adherence to surfaces E.g Streptococcus mutans and dental caries Capsule Important bacterial products 2:  Exotoxins: secreted by Gram positive bacteria E.g C tetani active immunity - toxoid  passive immunity - antitoxin  Bacterial cell walls Lipoteichoic . Nature and Properties of Micro-organisms Laura JV Piddock Smallest to largest…  Prions  Viruses . Shingles  Re-activation of latent infection  Suppression of cell mediated immunity Bacteria  Unicellular, prokaryotes  DNA and RNA  Binary fission