title: Listeria monocytogenes Strains Underrepresented during Selective Enrichment with an ISO Method Might Dominate during Passage through Simulated Gastric Fluid andIn VitroInfection of Caco-2 Cells.
abstract: VariousListeria monocytogenesstrains may contaminate a single food product, potentially resulting in simultaneous exposure of consumers to multiple strains. However, due to bias in strain recovery,L. monocytogenesstrains isolated from foods by selective enrichment (SE) might not always represent those that can better survive the immune system of a patient. We investigated the effect of cocultivation in tryptic soy broth with 0.6% yeast extract (TSB-Y) at 10°C for 8 days on (i) the detection ofL. monocytogenesstrains during SE with the ISO 11290-1:1996/Amd 1:2004 protocol and (ii) thein vitrovirulence of strains toward the Caco-2 human colon epithelial cancer cell line following exposure to simulated gastric fluid (SGF; pH 2.0)-HCl (37°C). We determined whether the strains which were favored by SE would be effective competitors under the conditions of challenges related to gastrointestinal passage of the pathogen. Interstrain competition ofL. monocytogenesin TSB-Y determined the relative population of each strain at the beginning of SE. This in turn impacted the outcome of SE (i.e., favoring survival of competitors with better fitness) and the levels exposed subsequently to SGF. However, strong growth competitors could be outcompeted after SGF exposure and infection of Caco-2 cells by strains outgrown in TSB-Y and underdetected (or even missed) during enrichment. Our data demonstrate a preferential selection of certainL. monocytogenesstrains during enrichments, often not reflecting a selective advantage of strains during infection. These findings highlight a noteworthy scenario associated with the difficulty of matching the source of infection (food) with theL. monocytogenesisolate appearing to be the causative agent during listeriosis outbreak investigations.IMPORTANCEThis report is relevant to understanding the processes involved in selection and prevalence of certainL. monocytogenesstrains in different environments (i.e., foods or sites of humans exposed to the pathogen). It highlights the occurrence of multiple strains in the same food as an important aspect contributing to mismatches between clinical isolates and infection sources during listeriosis outbreak investigations.
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Food Quality Control and Hygiene, Athens, Greece.
authors.forename: Evangelia
authors.initials: E
authors.lastname: Zilelidou
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Food Quality Control and Hygiene, Athens, Greece.
authors.forename: Christina-Vasiliki
authors.initials: CV
authors.lastname: Karmiri
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Dairy Research, Athens, Greece.
authors.forename: Georgia
authors.initials: G
authors.lastname: Zoumpopoulou
authors.affiliation: Laboratory of Cell Proliferation and Ageing, Institute of Biosciences and Applications, National Centre for Scientific Research Demokritos, Athens, Greece.
authors.forename: Eleni
authors.initials: E
authors.lastname: Mavrogonatou
authors.affiliation: Laboratory of Cell Proliferation and Ageing, Institute of Biosciences and Applications, National Centre for Scientific Research Demokritos, Athens, Greece.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kletsas
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Dairy Research, Athens, Greece.
authors.forename: Effie
authors.initials: E
authors.lastname: Tsakalidou
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Dairy Research, Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Papadimitriou
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Food Quality Control and Hygiene, Athens, Greece.
authors.forename: Eleftherios
authors.initials: E
authors.lastname: Drosinos
authors.affiliation: Agricultural University of Athens, Department of Food Science and Human Nutrition, Laboratory of Food Quality Control and Hygiene, Athens, Greece pskan@aua.gr.
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Skandamis