Molecular and metabolic typing of resident and transient fluorescent pseudomonad flora from a meat mincer

Abstract

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 unminced 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. fluorescens is successful in forming biofilm in this environment.