Molecular and Metabolic Typing of Resident and Transient Fluorescent Pseudomonad Flora from a Meat Mincer.

Nine spots on a meat mincer in a large catering facility were sampled four times over a three-month period after routine cleaning and disinfection. Spot 2 carried a significantly higher average microbial load than the other spots and was the only spot with a persistent population of fluorescent pseudomonads. The predominant type of fluorescent pseudomonads produced a yellow diffusible pigment and were always found in turkey meat. Since turkey was also the last type of meat minced on each working day, it was considered the likely source of these bacteria on the mincer. Sixty-three yellow-fluorescing pseudomonad strains from un-minced turkey and 17 strains from mincer spot 2 after mincing, cleaning, and disinfection were subjected to fingerprint analysis by random amplification of polymorphic DNA (RAPD) and by analysis of the assimilation patterns of 95 carbon sources using the Biolog system. Cluster analysis of the RAPD and the metabolic fingerprints revealed that all the mincer strains formed a homogeneous cluster, exclusive of all the turkey strains which displayed a higher degree of heterogeneity. Six strains isolated 1 week earlier and six strains isolated 11 weeks earlier from spot 2 were also subjected to RAPD analysis. Their fingerprints fell within the existing cluster of 17 spot 2 strains. These results suggest the existence on mincer spot 2 of an endemic flora of fluorescent pseudomonads, probably in the form of a biofilm. The genetic and physiological homogeneity of this flora, as opposed to the heterogeneity of the raw meat flora, indicates that only a fraction of the raw meat population of P. fiuorescens is successful in forming biofilm in this environment.

High-Pressure Transient Sensitization of Escherichia coli to Lysozyme and Nisin by Disruption of Outer-Membrane Permeability.

Escherichia coli MG1655 suspensions in 10 mM phosphate buffer (pH 7.0) were subjected to high pressures in the range of 180 to 320 MPa for 15 min. Cell death was evident at 220 MPa and increased exponentially with pressure. Surviving populations were sublethally injured, as demonstrated by their reduced ability to form colonies on violet red bile glucose agar, a selective growth medium containing crystal violet and bile salts. During exposure to high pressure (> 180 MPa), cells were sensitive to lysozyme, nisin, and ethylenediaminetetraacetic acid (EDTA), as was apparent from an increased lethality of pressure in the presence of these agents. Sublethal injury in the surviving population was lower in the presence of nisin and lysozyme, but higher in the presence of EDTA. Combinations of EDTA with nisin or lysozyme present during pressure treatment increased lethality in an additive manner. However, the addition of lysozyme, nisin and/or EDTA to pressurized cell suspensions immediately after pressure treatment did not cause any viable count reduction. Finally, we observed leakage of the periplasmic enzyme ß-lactamase from an ampicillin-resistant recombinant E. coli MG1655 under high pressure. These results suggest that high pressure transiently disrupts the permeability of the E. coli outer membrane for water-soluble proteins.