Production of acylated homoserine lactones by psychrotrophic members of the Enterobacteriaceae isolated from foods

Bacteria are able to communicate and gene regulation can be mediated throug h the production of acylated homoserine lactone (AHL) signal molecules. The se signals play important roles in several pathogenic and symbiotic bacteri a. The following study was undertaken to investigate whether AHLs are produ ced by bacteria found in food at temperatures and NaCl conditions commercia lly used for food preservation and storage. A minimum of 116 of 154 psychro trophic Enterobacteriaceae strains isolated from cold-smoked salmon or vacu um-packed chilled meat produced AHLs. Analysis by thin-layer chromatography indicated that N-3-oxohexanoyl homoserine lactone was the major AHL of sev eral of the strains isolated from cold-smoked salmon and meat. AHL-positive strains cultured at 5 degrees C in medium supplemented with 4% NaCl produc ed detectable amounts of AHL(s) at cell densities of 10(6) CFU/ml. AHLs wer e detected in cold-smoked salmon inoculated with strains of Enterobacteriac eae stored at 5 degrees C under an N-2 atmosphere when mean cell densities increased to 10(6) CFU/g and above. Similarly, AHLs were detected in uninoc ulated samples of commercially produced cold-smoked salmon when the level o f indigenous Enterobacteriaceae reached 106 CFU/g. This level of Enterobact eriaceae is often found in lightly preserved foods, and AHL-mediated gene r egulation may play a role in bacteria associated with food spoilage or food toxicity.