Listeria monocytogenesIsolates from Foods and Humans Form Distinct but Overlapping Populations

Abstract

. Assignment of isolates to lineages and to the majority of L. monocytogenes subtypes was significantly associated with the isolate source (food or human), although most subtypes and lineages included both human and food isolates. Some subtypes were also significantly associated with isolation from specific food types. Tissue culture plaque assay characterization of the 42 human isolates from Maryland and California and of 91 representative food isolates revealed significantly higher average infectivity and cell-to-cell spread for the human isolates, further supporting the hypothesis that food and human isolates form distinct populations. Combined analysis of subtype and cytopathogenicity data showed that strains classified into specific ribotypes previously linked to multiple human listeriosis outbreaks, as well as those classified into lineage I, are more common among human cases and generate larger plaques than other subtypes, suggesting that these subtypes may represent particularly virulent clonal groups. These data will provide a framework for prediction of the public health risk associated with specific L. monocytogenes subtypes.

Molecular Characterization and Serotyping of Listeria monocytogenes with a Focus on Food Safety and Disease Prevention

“…One major finding in this study is that the majority of the isolates found in food samples belonged to lineage III (4a, 4c), which is contrary to results found in previous studies (Gray et al, 2004;Ward et al, 2004). Isolates in lineage III are known to be more prevalent in animals with clinical Listeriosis (Jeffers et al, 2001).…”

First Report of Listeria monocytogenes Serotypes Detected from Milk and Milk Products in Sri Lanka

“…One major finding in this study is that the majority of the isolates found in dairy samples belong to lineage II [1/2a (or 3a), 1/2c (or 3c)] this is in line with the previous studies (Gray et al, 2004;Ward et al, 2004). This study alarms us the possible out breaks of Listeriosis.…”

Genetic and phenotypic characterization of Listeria monocytogenes lineage III

“…While over 40 % of the lineage III isolates characterized here came from human clinical cases of listeriosis, it is important to point out that human clinical isolates are overrepresented in our strain collection used to assemble the lineage III isolates set for this study. In general, lineage III isolates are more common among animal listeriosis cases (representing about 10 % of animal clinical isolates: Jeffers et al, 2001) than among human clinical isolates or food isolates, representing 2?2 % and 0?4 % of isolates in these two categories, respectively (Gray et al, 2004). Consistent with the results reported by Ward et al (2004), these data thus suggest that rarity of human exposure to lineage III isolates through consumption of contaminated foods, rather than reduced virulence, may account for the fact that lineage III isolates cause few human listeriosis cases and have never been linked to a human listeriosis outbreak.…”

“…For example, 10?5 % of the 76 animal isolates characterized by Jeffers et al (2001) were lineage III, while human lineage III prevalence has been consistently less than 2?5 % (Jeffers, 1998;Jeffers et al, 2001). While these findings led some to hypothesize that lineage III isolates may have reduced human pathogenic potential (Jeffers, 1998;Jeffers et al, 2001;Wiedmann et al, 1997), more recent data reporting an exceptionally low prevalence (<1?0 %) of lineage III among food isolates (Gray et al, 2004;Ward et al, 2004) suggest that the uncommon occurrence of human listeriosis cases due to lineage III strains may be explained by the rarity of foodborne exposure to these strains.…”