Salmonella – A Dangerous Foodborne Pathogen 164 The persistence of Salmonella within the food chain has become a major health concern, as biofilms of this pathogen formed in food processing environments can serve as a reservoir for the contamination of food products. The development of materials to be used for food- contact surfaces with improved food safety profiles continues to be a challenge. One approach which has been developed to control microbial attachment is the manufacture of food-contact materials incorporating antimicrobial compounds. Triclosan-impregnated kitchen bench stones (silestones), although prone to bacterial colonization, were found to reduce S. Enteritidis biofilm development on them and also the viability of cells within the biofilm (Rodrigues et al., 2011). 5. Molecular components of Salmonella biofilms formed on abiotic surfaces Curli fimbriae (formerly designated as thin aggregative fimbriae or Tafi) and cellulose are the two main matrix components (exopolymeric substances, EPS) in Salmonella biofilms (Gerstel & Römling, 2003). When co-expressed on Congo Red (CR) agar plates, curli fimbriae and the exopolysaccharide cellulose form the characteristic rdar (red, dry and rough) morphotype (also called rugose or wrinkled) (Römling, 2005). Their syntheses are co-regulated by a complex regulatory system. The LuxR type regulator CsgD protein stimulates the production of curli through transcriptional activation of the csgBAC (formerly agfBAC) operon, while the activation of cellulose production is indirect through the regulator AdrA which is a member of the GGDEF protein family regulated by csgD (Römling et al., 2000). García et al. (2004) demonstrated that most GGDEF proteins of S. Typhimurium are functionally related, probably by controlling the levels of the same final product, cyclic di-GMP, a secondary messenger that seems to regulate a variety of cellular functions including cellulose production and biofilm formation. The co-expression of curli fimbriae and cellulose leads to the formation of a highly hydrophobic network with tightly packed cells aligned in parallel in a rigid matrix and enhances biofilm formation on abiotic surfaces (Jain & Chen, 2007). Solomon et al. (2005) showed that 72% of 71 S. enterica strains, originating from produce, meat or clinical sources and belonging to 28 different serovars, expressed the rdar morphotype, with curli- and cellulose-deficient isolates being least effective in biofilm formation on polystyrene microtiter plates. White et al. (2006) showed that rdar morphotype significantly enhanced the resistance of Salmonella to dessication and sodium hypochlorite, suggesting that this phenotype could play a role in the transmission of Salmonella between hosts. However, aggregation via the rdar morphotype does not seem to be a virulence adaptation in S. Typhimurium, since competitive infection experiments in mice showed that nonaggregative cells outcompeted rdar-positive wild-type cells in all tissues analyzed (White et al., 2008). A variety of environmental cues such as nutrients, oxygen tension, temperature, pH, ethanol and osmolarity can influence the expression of the transcriptional regulator CsgD, which regulates the production of both cellulose and curli (Gerstel & Römling, 2003). Transcription of csgD is dependent upon the stationary phase-inducible sigma factor RpoS, and is maximal in the late exponential or early stationary phase of growth (Gerstel & Römling, 2001). For an extensive overview on the current understanding of the complex genetic network regulating Salmonella biofilm formation, reader is advised to refer to the recently published review of Steenackers et al. (2011). When csgD is not expressed the morphotype is a conventional smooth and white (saw) colony, which does not produce any extracellular matrix (Römling et al., 1998b). In wild type Salmonella strains, rdar morphotype is restricted to low temperature (below 30°C) and low osmolarity conditions, but biogenesis of curli Attachment and Biofilm Formation by Salmonella in Food Processing Environments 165 fimbriae occurs upon iron starvation at 37°C. Römling et al. (2003) showed that the majority (more than 90% of 800 strains) of human disease-associated S. Typhimurium and S. Enteritidis (isolated from patients, foods and animals) displayed the rdar morphotype at 28°C, but just rarely at 37°C. Interestingly, mutants in the csgD promoter have also been found expressing rdar morphotype independently of temperature (Römling et al., 1998b). Curli fimbriae are amyloid cell-surface proteins, and are involved in adhesion to surfaces, cell aggregation, environmental persistence and biofilm development (Austin et al., 1998; Collinson et al., 1991; White et al., 2006). The csg (curli subunit genes) genes (previously called agf genes) involved in curli biosynthesis are organized into two adjacent divergently- transcribed operons, csgBAC and csgDEFG (Collinson et al., 1996; Römling et al., 1998a). Knocking out the gene encoding for the subunit of thin aggregative fimbriae, AgfA, results in pink colony formation, the pdar (pink, dry and rough) morphotype, which is characterised by production of cellulose without curli (Jain & Chen, 2007). Solano et al. (2002) stressed the importance of the applied biofilm system since they noticed that curli were not essential for biofilm mediated glass adherence under adherence test medium (ATM) conditions, while they were indispensable to form a tight pellicle under LB conditions. In addition to curli, the second component of the extracellular matrix of the Salmonella biofilms is cellulose, a β-1→4-D-glucose polymer, which is biosynthesized by the bcsABZC- bcsEFG genes (bacterial cellulose synthesis) (Zogaj et al., 2001). Both operons are responsible for cellulose biosynthesis in both S. Enteritidis and S. Typhimurium (Jain & Chen, 2007; Solano et al., 2002). Cellulose production impaiment generates a bdar (brown, dry and rough) morphotype on congo red (CR) agar plates, characteristic of the expression of curli. Solano et al. (2002) showed that cellulose is a crucial biofilm determinant for Salmonella, under both LB and ATM conditions, without however affecting the virulence of the bacterium. Additionally, cellulose-deficient mutants were more sensitive to chlorine treatments, suggesting that cellulose production and biofilm formation may be an important factor for the survival of Salmonella in hostile environments. Prouty & Gunn (2003) identified its crucial importance for biofilm formation on glass coverslips. However, cellulose was not a major constituent of the biofilm matrix of S. Agona and S. Typhimurium strains isolated from the feed industry, but it contributed to the highly organized matrix structurization (Vestby et al., 2009a). Malcova et al. (2008) found that cellulose was not crucial for S. Enteritidis adherence and biofilm formation on polystyrene. Latasa et al. (2005) also reported another matrix component, BapA, a large cell-surface protein required for biofilm formation of S. Enteritidis. This protein was found to be loosely associated with the cell surface, while it is secreted through the BapBCD type I protein secretion system, encoded by the bapABCD operon. The expression of bapA was demonstrated to be coordinated with the expression of curli and cellulose through the action of csgD (Latasa et al., 2005). Also, these authors demonstrated that a bapA mutant strain showed a significant lower colonization rate at the intestinal cell barrier and consequently a decreased efficiency for organ invasion compared with the wild-type strain. Motility was found to be important for Salmonella biofilm development on glass (Prouty & Gunn, 2003) and polyvinyl chloride (PVC) (Mireles et al., 2001). On the contrary, Teplitski et al. (2006) noticed that the presence of the flagellum on the surface of the cell, functional or not, is inhibitory to biofilm formation on polystyrene, as mutants lacking intact flagella, showed increased biofilm formation compared to the wild-type. Flagella were not found to be important for S. Typhimurium rdar expression on Congo Red (CR) agar plates (Römling & Rohde, 1999). Solano et al. (2002) noticed that flagella affect S. Enteritidis biofilm development Salmonella – A Dangerous Foodborne Pathogen 166 only under LB but not under ATM conditions. Stafford & Hughes (2007) showed that the conserved flagellar regulon gene flhE, while it is not required for flagella production or swimming, appeared to play a role in flagella-dependent swarming and biofilm formation on PVC. Kim & Wei (2009) noticed that flagellar assemply was important during biofilm formation on PVC in different (meat, poultry and produce) broths and on stainless steel and glass in LB broth. Colanic acid, a capsular extracellular polysaccharide, essential for S. Typhimurium biofilm development on epithelial cells was found not to be required for Salmonella biofilm formation on abiotic surfaces (Ledeboer & Jones, 2005; Prouty & Gunn, 2003). Solano et al. (2002) showed that colonic acid was important to form a tight pellicle under LB conditions, while it was dispensable under ATM conditions. De Rezende et al. (2005) purified another capsular polysaccharide (CP) from extracellular matrix of multiresistant S. Typhimurium DT104 which was found to be important for biofilm formation on polystyrene centrifuge tubes and was detected at both 25°C and 37°C. This was comprised principally of glucose and mannose, with galactose as a minor constituent. Malcova et al. (2008) confirmed the importance of this capsular polysaccharide in the biofilm formation capacity of strains unable to produce either curli fimbriae or cellulose. Due to mucoid and brown appearance on Congo Red agar plates, their morphotype was designated as sbam (smooth, brown and mucoid). However, other capsular polysaccharides can be present in the extracellular biofilm matrix of Salmonella strains (de Rezende et al., 2005; Gibson et al., 2006; White et al., 2003), and the exact composition depends upon the environmental conditions in which the biofilms are formed (Prouty & Gunn, 2003). Another component of the EPS matrix of Salmonella bile-induced biofilms, the O-antigen (O-ag) capsule, while it was found to be crucial for S. Typhimurium and S. Typhi biofilm development on gallstones, this was not necessary for adhesion and biofilm formation on glass and plastic (Crawford et al., 2008). The formation of this O-ag capsule was also found to be important for survival during desiccation stress (Gibson et al., 2006). Anriany et al. (2006) highlighted the importance of an integral lipopolysaccharide (LPS), at both the O-antigen and core polysaccharide levels, in the modulation of curli protein and cellulose production, as well as in biofilm formation, thereby adding another potential component to the complex regulatory system which governs multicellular behavior in S. Typhimurium. Mireles et al. (2001) observed that for S. Typhimurium LT2, all of the LPS mutants examined were able to form a biofilm on polyvinyl chloride (PVC) but none were able to attach to a hydrophilic surface such as glass. Kim & Wei (2009) noticed that a rfbA mutant of S. Typhimurium DT104, showing an aberrant LPS profile, was impaired in rdar expression, pellicle formation, biofilm forming capability on PVC in meat, poultry and produce broths and biofilm formation on stainless steel and glass. 6. Cell-to-cell communication in Salmonella biofilms (quorum sensing) It has been thoroughly suggested that bacterial cells communicate by releasing and sensing small diffusible signal molecules, in a process commonly known as quorum sensing (QS) (Miller & Bassler, 2001; Smith et al., 2004; Whitehead et al., 2001). Through cell-to-cell signaling mechanisms, bacteria modulate their own behaviour and also respond to signal produced by other species (Ryan & Dow, 2008). QS involves a density-dependent recognition of signaling molecules (autoinducers, AIs), resulting in modulation of gene expression (Bassler, 1999). Gram-negative bacteria primarily use a variety of N- acylhomoserine lactones (AHLs) as AI (autoinducer-1, AI-1), while Gram-positive bacteria Attachment and Biofilm Formation by Salmonella in Food Processing Environments 167 use a variety of autoinducing polypeptides (AIPs). AHLs are synthesized and recognized by QS circuits composed of LuxI and LuxR homologues, respectively (Whitehead et al., 2001). Both AHLs and AIPs are highly specific to the species that produce them. A third QS system is proposed to be universal, allowing interspecies communication, and is based on the enzyme LuxS which is in part responsible for the production of a furanone-like compound, called autoinducer-2 (AI-2) (Schauder et al., 2001). Bacteria use QS communication circuits to regulate a diverse array of physiological activities, such as genetic competence, pathogenicity (virulence), motility, sporulation, bioluminescence and production of antimicrobial substances (Miller & Bassler, 2001). Yet, a growing body of evidence demonstrates that QS also contributes to biofilm formation by many different species (Annous et al., 2009; Davies et al., 1998; Irie & Parsek, 2008; Lazar, 2011). As biofilms typically contain high concentration of cells, autoinducer (AI) activity and QS regulation of gene expression have been proposed as essential components of biofilm physiology (Kjelleberg & Molin, 2002; Parsek & Greenberg, 2005). To date, three QS systems have been identified in S. enterica and are thought to be mainly implicated in the regulation of virulence (SdiA, luxS/AI-2 and AI-3/epinephrine/ norepinephrine signaling system) (Boyen et al., 2009; Walters & Sperandio, 2006). Firstly, the LuxR homologue SdiA has been characterized in Salmonella, but there does not appear to be a corresponding signal-generating enzyme similar to LuxI in this species (Ahmer et al., 1998). Since Salmonella does not possess a luxI homologue, it cannot produce its own AHLs (Ahmer, 2004). However, Salmonella SdiA can detect AHLs produced by a variety of bacterial species, leading to the suggestion that SdiA can be used in interspecies communication within a mixed-species community (Michael et al., 2001; Smith & Ahmer 2003). Till now, SdiA is known to activate the expression of the rck operon and the srgE gene (Ahmer et al., 1998; Smith & Ahmer, 2003). In contrast to the function of SdiA in E. coli adherence to HEp-2 epithelial cells and also biofilm formation on polystyrene (Lee et al., 2009; Sharma et al., 2010), no direct link between SdiA and Salmonella biofilms has been reported. Interestingly, Chorianopoulos et al. (2010) demonstrated that cell-free culture supernatant (CFS) of the psychrotrophic spoilage bacterium Hafnei alvei, containing AHLs among other unknown metabolites, negatively influenced the early stage of biofilm formation by S. Enteritidis on stainless steel. Similarly, Dheilly et al. (2010) reported the inhibitory activity of CFS from the marine bacterium Pseudoalteromonas sp. strain 3J6 against biofilm formation on glass flow cells by S. enterica and other Gram-negative bacteria. Taking into account that Salmonella possess SdiA, a receptor of AHLs which may be produced by resident flora on food-contact surfaces (Michael et al., 2001; Smith & Ahmer, 2003; Soares & Ahmer, 2011), the effect of AHLs on biofilm formation by this pathogen in multispecies real food processing environments needs to be further studied. The second QS system of Salmonella uses the LuxS enzyme for the synthesis of AI-2 (Schauder et al., 2001; Soni et al., 2008). The Lsr ABC transporter is known to be involved in the detection and transport of AI-2 into the cell (Taga et al., 2001), while the rbs transporter has recently been suggested as an alternative AI-2 uptake system (Jesudhasan et al., 2010). A S. Typhimurium luxS deletion mutant was impaired in biofilm formation on polystyrene (De Keersmaecker et al., 2005; Jesudhasan et al., 2010). However, this phenotype could not be complemented by extracellular addition of QS signal molecules, suggesting that AI-2 is not the actual signal involved in Salmonella biofilm formation (De Keersmaecker et al., 2005). To this direction, Kint et al. (2010) analyzed additional luxS mutants for their biofilm phenotype. Interestingly, a luxS kanamycin insertion mutant and a partial deletion mutant, Salmonella – A Dangerous Foodborne Pathogen 168 that only lacked the 3′ part of the luxS coding sequence, were found to be able to form mature wild-type biofilms on polystyrene, despite the fact that these strains were unable to produce AI-2. These authors concluded that a small regulatory RNA molecule, MicA, encoded in the luxS adjacent genomic region, rather than LuxS itself, infuences S. Typhimurium biofilm formation phenotype. On the other hand, Prouty et al. (2002) showed that a S. Typhimurium luxS insertion mutant formed scattered biofilm on gallstones with little apparent EPS even after 14 days of incubation. Yoon & Sofos (2008) showed that biofilm formation by S. Thompson on stainless steel, under monoculture conditions (72 h at 25°C), was similar between AI-2 positive and negative strains. Altogether, these results demonstrate that the relationship between biofilm formation and the presence of an active LuxS system and AI-2 in S. enterica is not clear and further research is needed. The third QS system of Salmonella uses the two component system PreA/B (Bearson & Bearson 2008; Merighi et al., 2006). PreA/B is similar to the luxS-dependent two component QseB/QseC of enterohemorrhagic E. coli, which has been shown to sense the QS signal AI-3, as well the eukaryotic hormones epinephrine and norepinephrine (Sperandio et al., 2002; Walters & Sperandio, 2006). In S. Typhimurium, the histidine sensor kinase QseC, which is able to detect norepinephrine, has been implicated in the regulation of virulence traits, such as motility and in vivo competitive fitness in pigs (Bearson & Bearson, 2008). Even though the role of AI-3/epinephrine/norepinephrine signaling system in the formation of biofilm by Salmonella is still unknown, given that motility is usually an important biofilm determinant in many bacterial species, it is quite possible that this third QS system may also affect Salmonella biofilm formation. 7. Conclusions Biofilms are commonly defined as communities of microorganisms attached to a surface and producing an extracellular matrix, in which these microorganisms are embedded. Biofilms are very diverse and unique, not just to the microorganism, but to the particular environment in which they are being formed. This makes in vitro characterization of biofilms difficult and requires the establishment of laboratory conditions that mimic the natural setting being studied. Pathogenic biofilms have been of considerable interest in the context of food safety and have provoked interest of many research groups. In particular, biofilm formation by Salmonella is a serious concern in food industry, since the persistence of this bacterium in biofilms formed on food-contact surfaces may become a constant source of product contamination. The discovery of bacterial biofilms in medical and industrial ecosystems has created an urgency to identify and characterize factors that are necessary for biofilm development, which may serve as targets for biofilm prevention and treatment. Thus, researchers in the fields of clinical, food, water, and environmental microbiology have begun to investigate microbiological processes from a biofilm perspective. As the pharmaceutical, health-care and food industries embrace this approach, novel strategies for biofilm formation and control will undoubtedly emerge. Particularly challenging is the attempt to understand the complexicity of the interactions within a biofilm community, since these interactions between the different species influence the final outcome of this community. Communication between species may include extracellular compounds whose sole role is to influence gene expression, metabolic cooperativity and competition, physical contact, and the production of antimicrobial exoproducts. One or all of these interactions may be Attachment and Biofilm Formation by Salmonella in Food Processing Environments 169 occurring simultaneously. The challenge becomes more intriguing given that microflora on inadequately cleaned and disinfected food processing surfaces is a complex community, contrary to the laboratory studied pure-species biofilms. Undoubtedly, a clearer understanding of the factors which influence microbial attachment to abiotic surfaces could provide the information necessary to modify processes in food processing environments in order to reduce microbial persistence and therefore reduce the contamination of food products. For instance, the understanding of bacterial attachment to solid surfaces, such as stainless steel, may help in the future development of surfaces with no or reduced attachment, or in developing an effective sanitation programme and thus reducing the potential contamination of processed products by spoilage or/and pathogenic bacteria. Undoubtedly, the ability to recognize how Salmonella attach to food-contact surfaces and form biofilms on them is an important area of focus, since a better understanding of this ability may provide valuable ways towards the elimination of this pathogenic bacterium from food processing environments and eventually lead to reduced Salmonella-associated human illness. 8. Acknowledgement Authors would like to acknowledge European Union project ProSafeBeef (ref. Food-CT- 2006-36241) within the 6 th Framework Programme for the financial support of some of the studies on Salmonella biofilms performed on our lab. 9. References Ahmer, B.M.M. (2004). Cell-to-cell signalling in Escherichia coli and Salmonella enterica. Molecular Microbiology, Vol.52, No.4, (January 2004), pp. 933-945 Ahmer, B.M.; van Reeuwijk, J.; Timmers, C.D.; Valentine, P.J. & Heffron, F. (1998). Salmonella typhimurium encodes an SdiA homolog, a putative quorum sensor of the LuxR family, that regulates genes on the virulence plasmid. Journal of Bacteriology, Vol.180, No.5, (March 1998), pp. 1185-1193 Annous, B.A.; Fratamico, P.M & Smith, J.L. (2009). Quorum sensing in biofilms: why bacteria behave the way they do. Journal of Food Science, Vol.74, No.1., pp. R24-R37 Anriany, Y.; Sahu, S.N.; Wessels, K.R.; McCann, L.M. & Joseph, S.W. (2006). Alteration of the rugose phenotype in waaG and ddhC mutants of Salmonella enterica serovar Typhimurium DT104 is associated with inverse production of curli and cellulose. Applied and Environmental Microbiology, Vol.72, No.7, (July 2006), pp. 5002-5012 Arnold, J.W. & Yates, I.E. (2009). Interventions for control of Salmonella: clearance of microbial growth from rubber picker fingers. Poultry Science, Vol.88, No.6, (June 2009), pp. 1292-1298 Asséré, A.; Oulahal, N. & Carpentier, B. (2008). Comparative evaluation of methods for counting surviving biofilm cells adhering to a polyvinyl chloride surface exposed to chlorine or drying. Journal of Applied Microbiology, Vol.104, No.6, (June 2008), pp. 1692-1702 Austin, J.W. & Bergeron, G. (1995). Development of bacterial biofilms in dairy processing lines. Journal of Dairy Research, Vol.62, No.3, (August 1995), pp. 509-519 Austin, J.W.; Sanders, G.; Kay, W.W. & Collinson, S.K. (1998). Thin aggregative fimbriae enhance Salmonella enteritidis biofilm formation. FEMS Microbiology Letters, Vol.162, No.2, (May 1998), pp. 295-301 Salmonella – A Dangerous Foodborne Pathogen 170 Bagge-Ravn, D.; Ng, Y.; Hjelm, M.; Christiansen, J.N.; Johansen, C. & Gram, L. (2003). The microbial ecology of processing equipment in different fish industries - analysis of the microflora during processing and following cleaning and disinfection. International Journal of Food Microbiology, Vol.87, No.3, (November 2003), pp. 239-250 Barnes, L.M.; Lo, M.F.; Adams, M.R. & Chamberlain, A.H. (1999). Effect of milk proteins on adhesion of bacteria to stainless steel surfaces. Applied and Environmental Microbiology, Vol.65, No.10, (October 1999), pp. 4543-4548 Bassler, B.L. (1999). How bacteria talk to each other: regulation of gene expression by quorum sensing. Current Opinion in Microbiology, Vol.2, No.6, (December 1999), pp. 582-587 Bearson, B.L. & Bearson, S.M. (2008). The role of the QseC quorum-sensing sensor kinase in colonization and norepinephrine-enhanced motility of Salmonella enterica serovar Typhimurium. Microbial Pathogenesis, Vol.44, No.4, (April 2008), pp. 271-278 Beloin, C.; Valle, J.; Latour-Lambert, P.; Faure, P.; Kzreminski, M.; Balestrino, D.; Haagensen, J.A.; Molin, S.; Prensier, G.; Arbeille, B. & Ghigo, J.M. (2004). Global impact of mature biofilm lifestyle on Escherichia coli K-12 gene expression. Molecular Microbiology, Vol.51, No.3, (February 2004), pp. 659-674 Bernbom, N.; Ng, Y.Y.; Jørgensen, R.L.; Arpanaei, A.; Meyer, R.L.; Kingshott, P.; Vejborg, R.M.; Klemm, P. & Gram, L. (2009). Adhesion of food-borne bacteria to stainless steel is reduced by food conditioning films. Journal of Applied Microbiology, Vol.106, No.4, (April 2009), pp. 1268-1279 Blackman, I.C. & Frank, J.F. (1996). Growth of Listeria monocytogenes as a biofilm on various food-processing surfaces. Journal of Food Protection, Vol.59, No.8, (August 1996), pp. 827-831 Boyen, F.; Eeckhaut, V.; Van Immerseel, F.; Pasmans, F.; Ducatelle, R. & Haesebrouck, F. (2009). Quorum sensing in veterinary pathogens: mechanisms, clinical importance and future perspectives. Veterinary Microbiology, Vol.135, No.3-4, (March 2009), pp. 187-195 Branda, S.S.; Vik, S.; Friedman, L. & Kolter, R. (2005). Biofilms: the matrix revisited. Trends in Microbiology, Vol.13, No.1, (January 2005), pp. 20-26 Briandet, R.; Meylheuc, T.; Maher, C. & Bellon-Fontaine, M.N. (1999). Listeria monocytogenes Scott A: cell surface charge, hydrophobicity, and electron donor and acceptor characteristics under different environmental growth conditions. Applied and Environmental Microbiology, Vol.65, No.12, (December 1999), pp. 5328-5333 Brooks, J.D. & Flint, S.H. (2008). Biofilms in the food industry: problems and potential solutions. International Journal of Food Science and Technology, Vol.43, (August 2008), pp. 2163-2176 Burmølle, M.; Webb, J.S.; Rao, D.; Hansen, L.H.; Sørensen, S.J. & Kjelleberg, S. (2006). Enhanced biofilm formation and increased resistance to antimicrobial agents and bacterial invasion are caused by synergistic interactions in multispecies biofilms. Applied and Environmental Microbiology, Vol.72, No.6, (June 2006), pp. 3916-3923 Carpentier, B. & Cerf, O. (1993). Biofilms and their consequences, with particular reference to hygiene in the food industry. Journal of Applied Bacteriology, Vol.75, (June 1993), pp. 499-451 Chia, T.W.R.; Goulter, R.M.; McMeekin, T.; Dykes, G.A. & Fegan, N. (2009). Attachment of different Salmonella serovars to materials commonly used in a poultry processing plant. Food Microbiology, Vol.26, (May 2009), pp. 853-859 Chmielewski, R.A.N. & Frank, J.F. (2003). Biofilm formation and control in food processing facilities. Comprehensive Reviews in Food Science and Food Safety, Vol.2, pp. 22-32 Attachment and Biofilm Formation by Salmonella in Food Processing Environments 171 Chorianopoulos, N.G.; Giaouris, E.D.; Kourkoutas, Y. & Nychas, G J. (2010). Inhibition of the early stage of Salmonella enterica serovar Enteritidis biofilm development on stainless steel by cell-free supernatant of a Hafnia alvei culture. Applied and Environmental Microbiology, Vol.76, No.6, (January 2010), pp. 2018-2022 Chorianopoulos, N.G.; Giaouris, E.D.; Skandamis, P.N.; Haroutounian, S.A. & Nychas, G J. (2008). Disinfectant test against monoculture and mixed-culture biofilms composed of technological, spoilage and pathogenic bacteria: bactericidal effect of essential oil and hydrosol of Satureja thymbra and comparison with standard acid-base santitizers. Journal of Applied Microbiology, Vol.104, No.6, (November 2007), pp. 1586-1596 Chorianopoulos, N.G.; Tsoukleris, D.S.; Panagou, E.Z.; Falaras, P. & Nychas, G.J. (2011). Use of titanium dioxide (TiO 2 ) photocatalysts as alternative means for Listeria monocytogenes biofilm disinfection in food processing. Food Microbiology, Vol.28, No.1, (February 2011), pp. 164-170 Collinson, S.K.; Clouthier, S.C.; Doran, J.L.; Banser, P.A. & Kay, W.W. (1996). Salmonella enteritidis agfBAC operon encoding thin, aggregative fimbriae. Journal of Bacteriology, Vol.178, No.3, (February 1996), pp. 662-667 Collinson, S.K.; Emödy, L.; Müller, K.H.; Trust, T.J. & Kay, W.W. (1991). Purification and characterization of thin, aggregative fimbriae from Salmonella enteritidis. Journal of Bacteriology, Vol.173, No.15, (August 1991), pp. 4773-4781 Cos, P.; Toté, K.; Horemans, T. & Maes, L. (2010). Biofilms: an extra hurdle for effective antimicrobial therapy. Current Pharmaceutical Design, Vol.16, No.20, pp. 2279-2295 Costerton, J.W.; Cheng, K.J.; Geesey, G.G.; Ladd, T.I.; Nickel, J.C.; Dasgupta, M. & Marrie, T.J. (1987). Bacterial biofilms in nature and disease. Annual Review of Microbiology, Vol.41, pp. 435-464 Costerton, J.W.; Lewandowski, Z.; Caldwell, D.E.; Korber, D.R. & Lappin-Scott, H.M. (1995). Microbial biofilms. Annual Review of Microbiology, Vol.49, pp. 711-745 Crawford, R.W.; Gibson, D.L.; Kay, W.W. & Gunn, J.S. (2008). Identification of a bile- induced exopolysaccharide required for Salmonella biofilm formation on gallstone surfaces. Infection and Immunity, Vol.76, No.11, (November 2008), pp. 5341-5349 Davey, M.E. & O’Toole, G.A. (2000). Microbial biofilms: from ecology to molecular genetics. Microbiology and Molecular Biology Reviews, Vol.64, No.4, pp. 847-867 Davies, D.G.; Parsek, M.R.; Pearson, J.P.; Iglewski, B.H.; Costerton, J.W. & Greenberg, E.P. (1998). The involvement of cell-to-cell signals in the development of a bacterial biofilm. Science, Vol.280, No.5361, (April 1998), pp. 295-298 De Keersmaecker, S.C.; Varszegi, C.; van Boxel, N.; Habel, L.W.; Metzger, K.; Daniels, R.; Marchal, K.; De Vos, D. & Vanderleyden, J. (2005). Chemical synthesis of (S)-4,5- dihydroxy-2,3-pentanedione, a bacterial signal molecule precursor, and validation of its activity in Salmonella typhimurium. Journal of Biological Chemistry, Vol.280, No.20, (May 2005), pp. 19563-19568 De Rezende, C.E.; Anriany, Y.; Carr, L.E.; Joseph, S.W. & Weiner, R.M. (2005). Capsular polysaccharide surrounds smooth and rugose types of Salmonella enterica serovar Typhimurium DT104. Applied and Environmental Microbiology, Vol.71, No.11, (November 2005), pp. 7345-7351 Dheilly, A.; Soum-Soutéra, E.; Klein, G.L.; Bazire, A.; Compère, C.; Haras, D. & Dufour, A. (2010). Antibiofilm activity of the marine bacterium Pseudoalteromonas sp. strain 3J6. Applied and Environmental Microbiology, Vol.76, No.11, (June 2010), pp. 3452-3461 Di Bonaventura, G.; Piccolomini, R.; Paludi, D.; D'Orio, V.; Vergara, A.; Conter, M. & Ianieri, A. (2008). Influence of temperature on biofilm formation by Listeria monocytogenes Salmonella – A Dangerous Foodborne Pathogen 172 on various food-contact surfaces: relationship with motility and cell surface hydrophobicity. Journal of Applied Microbiology, Vol.104, No.6, (June 2008), pp. 1552- 1561 Donlan, R.M. (2002). Biofilms: microbial life on surfaces. Emerging and Infectious Diseases, Vol.8, No.9, pp. 881-890 Donlan, R.M. & Costerton, J.W. (2002). Biofilms: survival mechanisms of clinically relevant microorganisms. Clinical Microbiology Reviews, Vol.15, No.2, pp. 167-193 Duguid, J.P.; Anderson, E.S. & Campbell, I. (1966). Fimbriae and adhesive properties in Salmonellae. Journal of Pathology and Bacteriology, Vol.92, No.1, (July 1966), pp. 107-138 EFSA-ECDC. (2011). The European Union summary report on trends and sources of zoonoses, zoonotic agents and food-borne outbreaks in 2009. The EFSA Journal, Vol.9, No.3:2090 Flemming, H.C. & Wingender, J. (2010). The biofilm matrix. Nature Reviews. Microbiology, Vol.8, No.9, (August 2010), pp. 623-633. Ganesh Kumar, S. & Anand, S.K. (1998). Significance of microbial biofilms in food industry: a review. International Journal of Food Microbiology, Vol.42, (April 1998), pp. 9-27 García, B.; Latasa, C.; Solano, C.; García-del Portillo, F.; Gamazo, C. & Lasa, I. (2004). Role of the GGDEF protein family in Salmonella cellulose biosynthesis and biofilm formation. Molecular Microbiology, Vol.54, No.1, (October 2004), pp. 264-277 Gawande, P.V. & Bhagwat, A.A. (2002). Inoculation onto solid surfaces protects Salmonella spp. during acid challenge: a model study using polyethersulfone membranes. Applied and Environmental Microbiology, Vol.68, No.1, (October 2001), pp. 86-92 Gerstel, U. & Römling, U. (2001). Oxygen tension and nutrient starvation are major signals that regulate agfD promoter activity and expression of the multicellular morphotype in Salmonella typhimurium. Environmental Microbiology, Vol.3, No.10, (October 2001), pp. 638-648 Gerstel, U. & Römling, U. (2003). The csgD promoter, a control unit for biofilm formation in Salmonella typhimurium. Research in Microbiology, Vol.154, No.10, (December 2003), pp. 659-667 Giaouris, E.; Chapot-Chartier, M.P. & Briandet, R. (2009). Surface physicochemical analysis of natural Lactococcus lactis strains reveals the existence of hydrophobic and low charged strains with altered adhesive properties. International Journal of Food Microbiology, Vol.131, No.1, (April 2009), pp. 2-9 Giaouris, E.; Chorianopoulos, N. & Nychas, G J.E. (2005). Effect of temperature, pH, and water activity on biofilm formation by Salmonella enterica Enteritidis PT4 on stainless steel surfaces as indicated by the bead vortexing method and conductance measurements. Journal of Food Protection, Vol.68, No.10, (May 2005), pp. 2149-2154 Giaouris, E.D. & Nychas, G J.E. (2006). The adherence of Salmonella Enteritidis PT4 to stainless steel: the importance of the air-liquid interface and nutrient availability. Food Microbiology, Vol.23, (February 2006), pp. 747-752 Gibson, D.L.; White, A.P.; Snyder, S.D.; Martin, S.; Heiss, C.; Azadi, P.; Surette, M. & Kay, W.W. (2006). Salmonella produces an O-antigen capsule regulated by AgfD and important for environmental persistence. Journal of Bacteriology, Vol.188, No.22, (November 2006), pp. 7722-7730 Gilbert, P.; Allison, D.G. & McBain, A.J. (2002). Biofilms in vitro and in vivo: do singular mechanisms imply cross-resistance? Journal of Applied Microbiology, Vol.92, pp. 98S- 110S Gilbert, P.; Evans, D.J. & Brown, M.R. (1993). Formation and dispersal of bacterial biofilms in vivo and in situ. Journal of Applied Bacteriology, Vol.74, Suppl.67S-78S Attachment and Biofilm Formation by Salmonella in Food Processing Environments 173 Girennavar, B.; Cepeda, M.L.; Soni, K.A.; Vikram, A.; Jesudhasan, P.; Jayaprakasha, G.K.; Pillai, S.D. & Patil, B.S. (2008). Grapefruit juice and its furocoumarins inhibits autoinducer signaling and biofilm formation in bacteria. International Journal of Food Microbiology, Vol.125, (March 2008), pp. 204-208 Goller, C.C. & Romeo, T. (2008). Environmental influences on biofilm development. Current Topics in Microbiology and Immunology, Vol.322, pp. 37-66 Gounadaki, A.S.; Skandamis, P.N.; Drosinos, E.H. & Nychas, G.J. (2008). Microbial ecology of food contact surfaces and products of small-scale facilities producing traditional sausages. Food Microbiology, Vol.25, No.2, (April 2008), pp. 313-323 Gunduz, G.T. & Tuncel, G. (2006). Biofilm formation in an ice cream plant. Antonie van Leeuwenhoek, Vol.89, pp. 329–336 Habimana, O.; Heir, E.; Langsrud, S.; Asli, A.W. & Møretrø, T. (2010a). Enhanced surface colonization by Escherichia coli O157:H7 in biofilms formed by an Acinetobacter calcoaceticus isolate from meat-processing environments. Applied and Environmental Microbiology, Vol.76, No.13, (July 2010), pp. 4557-4559 Habimana, O.; Møretrø, T.; Langsrud, S.; Vestby, L.K.; Nesse, L.L. & Heir, E. (2010b). Micro ecosystems from feed industry surfaces: a survival and biofilm study of Salmonella versus host resident flora strains. BMC Veterinary Research, Vol.6, No. 48 Hall-Stoodley, L.; Costerton, J.W. & Stoodley, P. (2004). Bacterial biofilms: from the natural environment to infectious diseases. Nature Reviews. Microbiology, Vol.2, (February 2004), pp. 95-108 Hall-Stoodley, L. & Stoodley, P. (2002). Developmental regulation of microbial biofilms. Current Opinion in Biotechnology, Vol.13, No.3, (June 2002), pp. 228-233 Hall-Stoodley, L. & Stoodley, P. (2005). Biofilm formation and dispersal and the transmission of human pathogens. Trends in Microbiology, Vol.13, No.1, (January 2005), pp. 7-10 Hamilton, S.; Bongaerts, R.J.; Mulholland, F.; Cochrane, B.; Porter, J.; Lucchini, S.; Lappin- Scott, H.M. & Hinton, J.C. (2009). The transcriptional programme of Salmonella enterica serovar Typhimurium reveals a key role for tryptophan metabolism in biofilms. BMC Genomics, Vol.10, (December 2009), 599 Hood, S.K. & Zottola, E.A. (1997a). Adherence to stainless steel by foodborne microorganisms during growth in model food systems. International Journal of Food Microbiology, Vol.37, (June 1997), pp. 145-153 Hood, S.K. & Zottola, E.A. (1997b). Growth media and surface conditioning influence the adherence of Pseudomonas fragi, Salmonella typhimurium, and Listeria monocytogenes cells to stainless steel. Journal of Food Protection, Vol.60, No.9, (January 1997), pp. 1034-1037 Humphrey, T.J.; Slater, E.; McAlpine, K.; Rowbury, R.J. & Gilbert, R.J. (1995). Salmonella Enteritidis Phage Type 4 isolates more tolerant of heat, acid, or hydrogen peroxide also survive longer on surfaces. Applied and Environmental Microbiology, Vol.61, No.8, (May 1995), pp. 3161-3164 Iibuchi, R.; Hara-Kudo, Y.; Hasegawa, A. & Kumagai, S. (2010). Survival of Salmonella on a polypropylene surface under dry conditions in relation to biofilm-formation capability. Journal of Food Protection, Vol.73, No.8, (December 2009), pp. 1506-1510 Irie, Y. & Parsek, M.R. (2008). Quorum sensing and microbial biofilms. Current Topics in Microbiology and Immunology, Vol.322, pp. 67-84 Jain, S. & Chen, J. (2007). Attachment and biofilm formation by various serotypes of Salmonella as influenced by cellulose production and thin aggregative fimbriae biosynthesis. Journal of Food Protection, Vol.70, No.11, (November 2007), pp. 2473-2479 [...]... natural habitat of Salmonella may be divided into three categories based on the specificity of the host and clinical pattern of the disease: highly adapted to men: Salmonella Typhi and Salmonella Paratyphi A, B and C, agents of typhoid fever; highly adapted to animals: Salmonella Dublin (bovines), Salmonella Choleraesuis and Salmonella Typhisuis (swine), Salmonella Pullorum and Salmonella Gallinarum... enterica subsp enterica (1,547 serovars); Salmonella enterica subsp salamae (513); Salmonella enterica subsp arizonae (100); Salmonella enterica subsp diarizonae (341); Salmonella enterica subsp Important Aspects of Salmonella in the Poultry Industry and in Public Health 183 houtenae (73); Salmonella enterica subsp indica (13); Salmonella bongori (23); the newly proposed species Salmonella subterranea was... thin aggregative fimbriae of Salmonella enterica serovar Enteritidis Journal of Bacteriology, Vol. 185 , No. 18, (September 2003), pp 53 98- 5407 180 Salmonella – A Dangerous Foodborne Pathogen White, A. P.; Gibson, D.L.; Grassl, G .A. ; Kay, W.W.; Finlay, B.B.; Vallance, B .A & Surette, M,G (20 08) Aggregation via the red, dry, and rough morphotype is not a virulence adaptation in Salmonella enterica serovar... from human sources were Salmonella Typhimurium, Salmonella Enteritidis, Salmonella Newport, Salmonella Heidelberg and Salmonella Javiana (Centers For Diseases Control and Prevention - CDC, 2007)  186 Salmonella – A Dangerous Foodborne Pathogen In Denmark, Salmonella Infantis was isolated from samples of pork, which was pointed out as the source human infection (Wegener & Baggesen, 1996) In several industrialized... positive catalase, negative oxidase; they ferment sugars with gas production, produce H2S, are nonsporogenic, and are normally motile with peritricheal flagella, except for Salmonella Pullorum and Salmonella Gallinarum, which are nonmotile (Forshell & Wierup, 2006)  182 Salmonella – A Dangerous Foodborne Pathogen Optimal pH for multiplication is around 7.0; pH values above 9.0 or below 4.0 are bactericidal... the Bergey’s manual, all Salmonella serotypes belong to one of two species: Salmonella bongori, which has at least 10 extremely rare serotypes; and Salmonella enterica, which is phenotypically and genotypically divided into six subspecies enterica, salamae, arizonae, diarizonae, houtenae and indica, differentiated by their biochemical behavior, mainly in terms of sugar and amino acid metabolism (Forshell... Brazil [ANVISA; Agência Nacional de Vigilância Sanitária], among the etiological agents of foodborne diseases identified between 1999 and 2004, Salmonella spp was the most prevalent in Brazil, with the predominance of Salmonella Enteritidis between 2001 and august 2005 (Rodrigues, 2005) According to the WHO, Salmonella is one of the pathogens that causes the greatest impact on population health, and... hours (Franco & Landgraf, 1996) The combination of the antigens O, H1 (flagellar, phase 1) and H2 (flagellar, phase 2) determine the antigenic formula of a serovar O antigens receive Arabic numerals, whereas H1 antigens are identified by lowercase letters, and H2 antigens by Arabic numerals For example, Salmonella enterica subsp salamae ser 50: z : e,n,x, or Salmonella serotype II 50: z : e,n,x Somatic... to remain viable in frozen products for long periods After entering the digestive system together with contaminated food and water, Salmonellae reach the intestines, where they attach to intestinal cells and multiply Depending on the host species and age, and on the pathogenicity of the microorganism 188 Salmonella – A Dangerous Foodborne Pathogen and its adaptation to the host, Salmonellae may cause... wall, and prevents detection of the somatic antigen It is usually found in strains of Salmonella Typhi, Salmonella Paratyphi C and Salmonella Dublin Vi antigens are thermolabile, and may be destroyed by heating at 100oC for 10-15 minutes The somatic antigen, or “O” (Ohne), on the other hand, is specific It is a lipopolysaccharide, and is resistant to heat and alcohol It is made up of three parts: a . is as follows: Salmonella enterica subsp. enterica (1,547 serovars); Salmonella enterica subsp salamae (513); Salmonella enterica subsp arizonae (100); Salmonella enterica subsp diarizonae. and C, agents of typhoid fever; highly adapted to animals: Salmonella Dublin (bovines), Salmonella Choleraesuis and Salmonella Typhisuis (swine), Salmonella Pullorum and Salmonella Gallinarum. phenotype. Interestingly, a luxS kanamycin insertion mutant and a partial deletion mutant, Salmonella – A Dangerous Foodborne Pathogen 1 68 that only lacked the 3′ part of the luxS coding