Plasmid profiles of Listeria species associated with poultry processing

Abstract

Since Listeria is frequently associated with poultry products, a study was undertaken to determine sources and prevalence of Listeria species and plasmid profile types in a South African poultry processing plant. Listeria were isolated by a standard enrichment procedure from chicken carcass neck skins sampled at six points during processing and from swabs of two equipment surfaces. The survey was repeated five times at monthly intervals (July-November). Isolates from Listeria positive samples were identified to species level and plasmid profiles of each isolate were determined. Listeria innocua was detected on the rubber fingers of the plucking machines and all neck skin samples after evisceration. Listeria monocytogenes strains were detected on the rubber fingers, packaging funnel and all neck skins after spin chilling. Of the Listeria species isolated, 77·2% corresponded to 1 of 2 different plasmid profile types which were distributed throughout all the Listeria positive sampling points. The frequency of occurrence of both species varied from month to month, but both predominant plasmid profile types occurred whenever Listeria positive samples were found. It was concluded that Listeria contamination of carcasses in the plant was due to faecal or gut contamination from the chickens or the presence of endemic Listeria strains.