Characterization and Pathogenic Potential ofListeria monocytogenesIsolates from the Smoked Fish Industry

Abstract

This study was designed to evaluate the hypothesis that some of the Listeria monocytogenes subtypes associated with foods, specifically smoked fish, may have an attenuated ability to cause human disease. We tested this hypothesis by using two different approaches: (i) comparison of molecular subtypes found among 117 isolates from smoked fish, raw materials, fish in process, and processing environments with subtypes found among a collection of 275 human clinical isolates and (ii) the evaluation of the cytopathogenicity of industrial isolates. Ribotyping and PCR-restriction fragment length polymorphism typing of the hlyA and actA genes differentiated 23 subtypes among the industrial isolates and allowed classification of the isolates into three genetic lineages. A significantly higher proportion of human isolates (69.1%) than industrial isolates (36.8%) were classified as lineage I, which contains human sporadic isolates and all epidemic isolates. All other industrial isolates (63.2%) were classified as lineage II, which contains only human sporadic isolates. Lineage I ribotypes DUP-1038B and DUP-1042B represented a significantly higher proportion of the human isolates than industrial isolates (5.1%). Lineage II ribotypes DUP-1039C, DUP-1042C, and DUP-1045, shown previously to persist in the smoked fish processing environment, represented nearly 50% of the industrial isolates, compared to 7.6% of the human isolates. Representatives of each subtype were evaluated with a tissue culture plaque assay. Lineage I isolates formed plaques that were significantly larger than those formed by lineage II isolates. Isolates from the smoked fish industry representing three ribotypes formed no plaques or small plaques, indicating that they had an impaired ability to infect mammalian cells. While L. monocytogenes clonal groups linked to human listeriosis cases and outbreaks were isolated, our data also suggest that at least some L. monocytogenes subtypes present in ready-to-eat foods may have limited human-pathogenic potential.Listeria monocytogenes is responsible for nearly one-fourth of all estimated food-borne-disease-related deaths caused by known pathogens in the United States each year, which highlights its significance as a public health concern (25). The majority of human listeriosis cases occur in pregnant women, neonates, immunosupressed individuals, and the elderly (12). As a growing segment of our population falls into high-risk groups, improved methods for reducing the levels of L. monocytogenes in foods are essential. A better understanding of the ecology, transmission, and pathogenicity of this organism should facilitate development of effective strategies.While L. monocytogenes causes relatively few human disease cases, particularly compared to many other food-borne pathogens (25), it appears to be commonly present in raw and readyto-eat foods. U.S. Department of Agriculture data, for example, indicated a 2.5% prevalence of L. monocytogenes in 3,547 samples of ready-to-eat products surveyed in 1998 and a 4.6 and 2...

Isolation of Listeria monocytogenes from the Skin of Slaughtered Beef Cattle

“…A previous study reported isolation of L. monocytogenes from cow stools, carcasses and meat products, and suggested that feces was the most likely source of contamination of the carcasses [3]. The pathogen has also been isolated from environments such as slaughterhouses and sewage, sludge and food-processing plants [4,8,9]. These reports suggest the presence of various sources of L. monocytogenes contamination in the environment.…”

“…Previous studies have isolated L. monocytogenes from food processing environment [4,9,11]. Animal food products, such as milk, dairy and meat products, have been suggested as especially important infectious sources of the pathogen.…”

Pulsed-Field Gel Electrophoresis (PFGE) Analysis of Temporally Matched Listeria monocytogenes Isolates from Human Clinical Cases, Foods, Ruminant Farms, and Urban and Natural Environments Reveals Source-Associated as Well as Widely Distributed PFGE Types

“…While a third lineage (termed lineage III) has been described as including serotypes 4a and 4c, as well as some serotype 4b strains (37,57,59), a recent study indicates the existence of multiple lineages within L. monocytogenes that include isolates with these serotypes (45). Different studies (23,41) have shown that lineage I strains are generally overrepresented among human isolates, while lineage II strains appear to be overrepresented among food isolates (41). Lineage III strains are rare but have been shown to be overrepresented among isolates from animal listeriosis cases (29).…”

Article

“…En effet, entre 5 et 10°C, la croissance est relativement lente, les taux maximum observés excèdent rarement 100-1000 UFC·g -1 [11]. De plus, le potentiel pathogène de souches de L. monocytogenes isolées du saumon fumé semble faible [37].…”