Understanding how bacteria communicate.

Bacteria talk to each other, and the implications of this capability are becoming apparent to microbiologists. This communication occurs at several levels: intraspecies (like-bacteria talking to like-bacteria); interspecies (communication among bacteria of different species and genera); and bacteria to host (bacterial communication with mammalian cells).

This communication is achieved by the production of small molecules, autoinducers, which, when present at sufficient concentrations, trigger a variety of cellular responses. Thus, bacterial numbers must reach a certain level, or quorum, to generate the critical concentration of these signaling molecules. This has led to the term "quorum sensing" to describe this phenomenon.

Quorum sensing--communication--controls a number of phenotypes in bacteria including biofilm formation, the synthesis of extracellular enzymes and the expression of virulence factors in many enteric bacteria. If we can understand how bacteria communicate, we may be able to develop strategies to interfere with this communication. This may lead to a reduction in the levels of biofilms found in food processing environments, an extended product shelf life (through the inhibition of the synthesis of proteases and lipases responsible for degrading foods) and a reduction in foodborne illness by preventing expression of virulence.

Quorum sensing enables microbes to coordinate their behavior in response to changes in their environment. They are able to adapt to the availability of nutrients, for example, by synthesizing extracellular enzymes that 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.

Of 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. 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 manner.

Interspecies communication in Gram negative bacteria is mediated through the production of autoinducer-2 (AI-2). The production of several virulence factors by E. coli O157:H7 are regulated by AI-2. Another autoinducer, AI-3, allows E. coli O157:H7 to talk to its host.

Further information. Mansel Griffiths, Department of Food Science, University of Guelph, Canadian Research Institute for Food Safety, Room 202, 43 McGilvray St., Guelph, ON, N1G 2W1, Canada; phone: [phone]; fax: [phone]; email: [e-mail].