[show abstract][hide abstract] ABSTRACT: In the process of evaluating the role of acylated homoserine lactones (AHLs) in food-spoiling Gram-negative bacteria, we have combined a range of bacterial AHL monitor systems to determine the AHL-profile and the kinetics of AHL-production. AHL production from 148 strains of Enterobacteriaceae isolated from foods was tested using Escherichia coli pSB403 (LuxR), Agrobacterium tumefaciens A136 (TraR) and both induction and inhibition of Chromobacterium violaceum CV026 (CviR). All strains except one was found to produce AHL(s). In no case could a single monitor system identify more than 64% of the Enterobacteriaceae as AHL-producers, showing that the simultaneous use of monitor strains is required in the process of screening bacterial populations for AHL-production. AHLs from 20 selected strains were profiled by thin layer chromatography. Most strains produced more than one AHL with 3-N-oxo-hexanoyl homoserine lactone being the most prominent. It was found that the simultaneous use of monitor strains in the top-layer was necessary for the detection of (presumably) all the AHLs. An agar well-diffusion assay based on A. tumefaciens pDZLR4 was used for quantifying AHLs from bacterial supernatants and enabled an assessment of the kinetics of AHL-production of 3 strains (Serratia proteamaculans strain B5a, Erwinia carotovora ATCC 39048 and V. fischeri strain MJ-1). As expected, the production of AHL (OHHL) and luminescence in Vibrio fischeri strain MJ-1 increased faster than growth indicating up-regulation of the AHL regulated phenotype and auto-induction of AHL production. In contrast, production kinetics of AHL (OHHL) in the two Enterobacteriaceae indicated lack of auto-induction.
Journal of Microbiological Methods 05/2001; 44(3):239-51. · 2.16 Impact Factor
[show abstract][hide abstract] ABSTRACT: Bacteria are able to communicate and gene regulation can be mediated through the production of acylated homoserine lactone (AHL) signal molecules. These signals play important roles in several pathogenic and symbiotic bacteria. The following study was undertaken to investigate whether AHLs are produced by bacteria found in food at temperatures and NaCl conditions commercially used for food preservation and storage. A minimum of 116 of 154 psychrotrophic Enterobacteriaceae strains isolated from cold-smoked salmon or vacuum-packed chilled meat produced AHLs. Analysis by thin-layer chromatography indicated that N-3-oxo-hexanoyl homoserine lactone was the major AHL of several of the strains isolated from cold-smoked salmon and meat. AHL-positive strains cultured at 5 degrees C in medium supplemented with 4% NaCl produced detectable amounts of AHL(s) at cell densities of 10(6) CFU/ml. AHLs were detected in cold-smoked salmon inoculated with strains of Enterobacteriaceae 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 uninoculated samples of commercially produced cold-smoked salmon when the level of indigenous Enterobacteriaceae reached 10(6) CFU/g. This level of Enterobacteriaceae is often found in lightly preserved foods, and AHL-mediated gene regulation may play a role in bacteria associated with food spoilage or food toxicity.
Applied and Environmental Microbiology 09/1999; 65(8):3458-63. · 3.68 Impact Factor