Listeria monocytogenes Serogroup 1/2 Strains Have a Competitive Growth Advantage over Serotype 4b during Refrigerated Storage of an Artificially Contaminated Ready-To-Eat Pork Meat Product

Abstract

Listeria monocytogenes is the bacterial causative agent of listeriosis, a life-threatening disease for humans, mainly transmitted through contaminated food. Human clinical isolates of the pathogen are frequently identified as serotype 4b strains; interestingly, however, serotype 4b (lineage I) is normally underrepresented among the food isolates in which serotype 1/2a (lineage II) is usually prevalent. The present study aimed to assess in situ dominance dynamics for the most commonly detected serotypes of L. monocytogenes implicated in foodborne listeriosis cases. A four-strain mixture comprised of L. monocytogenes serogroup 1/2 (i.e., serotypes 1/2a, 1/2b, and 1/2c) and serotype 4b food isolates was inoculated on a sliced ready-to-eat pork meat product, and dominance rates for the pathogenic strains were estimated based on serotype recoveries by utilizing multiplex polymerase chain reaction (mPCR), during storage of the product at 4 °C and 10 °C. The cumulative mPCR results showed that serotype 4b decreased at both storage temperatures, with the most abrupt decrease being noticed during storage at 10 °C. Irrespective of the storage temperature applied, L. monocytogenes strains of serogroup 1/2 predominated at the end of the meat product’s storage period. Conclusively, the preliminary findings of this research suggested a competitive growth advantage of L. monocytogenes serogroup 1/2 strains over serotype 4b during the refrigerated shelf-life of foods, thus advancing our knowledge on the pathogen’s behavior and contributing toward elucidating the manifested underrepresentation of serotype 4b in favor of serogroup 1/2 strains among the food isolates of the pathogen, particularly those recovered during detection and/or enumeration of L. monocytogenes in meat and products thereof.