Listeria monocytogenes Virulence and Pathogenicity, a Food Safety Perspective

Abstract

Several virulence factors of Listeria monocytogenes have been identified and extensively characterized at the molecular and cell biologic levels, including the hemolysin (listeriolysin O), two distinct phospholipases, a protein (ActA), several internalins, and others. Their study has yielded an impressive amount of information on the mechanisms employed by this facultative intracellular pathogen to interact with mammalian host cells, escape the host cell's killing mechanisms, and spread from one infected cell to others. In addition, several molecular subtyping tools have been developed to facilitate the detection of different strain types and lineages of the pathogen, including those implicated in common-source outbreaks of the disease. Despite these spectacular gains in knowledge, the virulence of L. monocytogenes as a foodborne pathogen remains poorly understood. The available pathogenesis and subtyping data generally fail to provide adequate insight about the virulence of field isolates and the likelihood that a given strain will cause illness. Possible mechanisms for the apparent prevalence of three serotypes (1/2a, 1/2b, and 4b) in human foodborne illness remain unidentified. The propensity of certain strain lineages (epidemic clones) to be implicated in common-source outbreaks and the prevalence of serotype 4b among epidemic-associated stains also remain poorly understood. This review first discusses current progress in understanding the general features of virulence and pathogenesis of L. monocytogenes. Emphasis is then placed on areas of special relevance to the organism's involvement in human foodborne illness, including (i) the relative prevalence of different serotypes and serotype-specific features and genetic markers; (ii) the ability of the organism to respond to environmental stresses of relevance to the food industry (cold, salt, iron depletion, and acid); (iii) the specific features of the major known epidemic-associated lineages; and (iv) the possible reservoirs of the organism in animals and the environment and the pronounced impact of environmental contamination in the food processing facilities. Finally, a discussion is provided on the perceived areas of special need for future research of relevance to food safety, including (i) theoretical modeling studies of niche complexity and contamination in the food processing facilities; (ii) strain databases for comprehensive molecular typing; and (iii) contributions from genomic and proteomic tools, including DNA microarrays for genotyping and expression signatures. Virulence-related genomic and proteomic signatures are expected to emerge from analysis of the genomes at the global level, with the support of adequate epidemiologic data and access to relevant strains.

Microbial contamination after sanitation of food contact surfaces in dairy and meat processing plants

“…This is in agreement with the general findings that raw meat and its products are most frequently contaminated with this pathogen (Farber & Peterkin 1991;Chen et al 2009). Furthermore, l. monocytogenes normally occurs in raw material and raw food products while its occurrence in heated products is a consequence of either inadequate heat treatment or re-contamination after heating (Kathariou 2002). In this study, none of the examined heat-treated products was positive for l. monocytogenes and none of the l. monocytogenes isolates belonged to serovar 4b, which was described as the most frequent causative agent of the invasive form of listeriosis before June, 2007, in Europe (Goulet et al 2008).…”

Listeria monocytogenesl‐forms respond to cell wall deficiency by modifying gene expression and the mode of division

“…Listeria is widely distributed in the environment and also occurs in the intestinal tract of healthy animals and humans. The L. monocytogenes strain Scott A used here is of serovar 4b, the most common cause of human epidemic listeriosis (Kathariou, 2002). It has been isolated during a listeriosis outbreak (Fleming et al, 1985), where the bacteria could be recovered from clinical cases but not from the pasteurized milk considered to be the source of the outbreak.…”

Evaluation of the efficacy of commercial sanitizers against adhered and planktonic cells of Listeria monocytogenes and Salmonella spp.

“…The to attach to surfaces and, eventually, to form biofilms (JENSEN; LAMMERT, 2003). In fact, it has been proved that Salmonella and L. monocytogenes cells are able to attach to different solid surfaces (SINDE; CARBALLO, 2000;BERESFORD;ANDREW;SHARMA, 2001;RAMESH et al, 2002) and they are present in food industrial environments (LO FO WONG et al, 2002;KATHARIOU, 2002).…”