The PlcB phospholipase C, or lecithinase, is an important listerial virulence factor of potential use as a pathogenicity marker for Listeria spp. food isolates. However, wild-type strains of Listeria monocytogenes express virulence factors very poorly in vitro and their lecithinase activity is normally difficult to detect on agar plates. We recently reported that the production of listerial virulence factors is strongly induced if L. monocytogenes is grown in the presence of activated charcoal. We report here a simple method for the rapid differentiation of L. monocytogenes from other Listeria spp. based on a comparison of lecithinase reactions in egg yolk agar plates with and without charcoal supplementation. All L. monocytogenes wild-type isolates tested showed a clear induction of lecithinase activity in charcoal-supplemented medium (CEYM), while nonpathogenic Listeria spp. remained negative in CEYM. The animal pathogen L. ivanovii was easily differentiated from L. monocytogenes because it showed a strong lecithinase reaction independently of the presence or absence of charcoal in the medium.
- Enzyme Activation/drug effects
- Food Contamination/analysis
- Food Microbiology
- Listeria monocytogenes/classification
- Listeria monocytogenes/enzymology
- Listeria monocytogenes/pathogenicity
- Species Specificity