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M. W. GRIFFITHS, Dept. of Food Science, Univ. of Guelph, Canadian Research Institute for Food Safety, 43 McGilvray St., Guelph, ON N1G 2W1, Canada Bacteria talk to each other and the implications of this are becoming apparent to food microbiologists. This communication occurs at several levels; intraspecies (like talking to like) interspecies (communication among bacteria of different species and genera), and bacteria – host (communication with mammalian cells). This communication is achieved by the production of small molecules (termed autoinducers), which, when present at sufficient concentrations, trigger a variety of cellular responses. Thus, bacterial numbers must reach a certain level (quorum) to generate the critical concentration of these signaling molecules. This has led to the term quorum sensing to describe this phenomenon. Quorum sensing allows bacteria to co-ordinate their behaviour in response to changes in their environment. These responses include adaptation to availability of nutrients, for example through the synthesis of extracellular enzymes to scavenge nutrients or through the formation of biofilms. Quorum sensing also provides a way to compete with other microorganisms and to avoid potentially toxic compounds. Arguably of greatest significance is the role that quorum sensing plays in pathogenesis. It allows pathogenic bacteria to reach high populations before producing virulence factors that elicit an immune response in the host. In this way a successful infection can be established. Different bacterial species use different molecules to communicate. In Gram negative bacteria, the main signaling molecules are acyl homoserine lactones whereas in Gram positive bacteria peptides, such as nisin, are the primary means of communication. However, a single bacterial species can use more than one signal molecule, and it may respond to each molecule in a different way. Interspecies communication in Gram negative bacteria is mediated through the production of autoinducer-2 (AI-2), and the production of several virulence factors by E. coli O157:H7 are regulated by AI-2. Recently, another autoinducer (AI-3) has been discovered that allows E. coli O157:H7 to talk to its host.
Session 20, Application and use of genomics in food microbiology
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