Academic journal article Journal of Health Population and Nutrition

Prevalence of Listeria Monocytogenes in Raw Meats Marketed in Bangkok and Characterization of the Isolates by Phenotypic and Molecular Methods

Academic journal article Journal of Health Population and Nutrition

Prevalence of Listeria Monocytogenes in Raw Meats Marketed in Bangkok and Characterization of the Isolates by Phenotypic and Molecular Methods

Article excerpt

INTRODUCTION

Listeria monocytogenes, a Gram-positive intracellular bacterium, causes foodborne listeriosis. The bacteria can grow under a wide range of temperature and conditions, and these are, thus, ubiquitous (1). L. monocytogenes strains attach to environmental surfaces and form biofilms, perhaps by using peritrichous flagella encoded by flaA gene (2). The biofilm formation renders the organisms more resistant to harsh environmental conditions, such as food processing, antibiotics, and detergents (3,4).

Humans are infected by consuming contaminated food. Only a fraction of the infected persons are, however, afflicted while others remain asymptomatic but may harbour the organism in their gastrointestinal tracts (5). The interplay among the host immunity, especially the innate and cell-mediated, the infecting dose, and the virulence of the bacteria regulates the outcome of infection (6). Clinical manifestations of listeriosis range from gastrointestinal disturbances, i.e. non-bloody diarrhoea, nausea, and vomiting, to influenza-like illness with high fever, headache, and myalgia, and to serious septicaemia and meningitis (7). Individuals prone to symptomatic listeriosis include infants, elderly, pregnant women, and those with the underlying conditions which impair their immune functions, such as malnutrition, major surgery, low gastric acidity, and lack of physical fitness (8,9). Pregnant women infected with L. monocytogenes may have spontaneous abortions, stillborn foetuses, or newborns with meningitis (10-12).

Several virulence factors contribute to the pathogenicity of L. monocytogenes. The ingested bacteria use several factors, including internalins (Inls), invasion-associated protein encoded by iap, murein hydrolase enzyme (p60), surface protein p104, and actA protein encoded by actA, to invade the intestinal epithelium via the epithelial tight junction and enter the enterocytes from the lateral surface (13). M cells also endocytose and transport the bacteria to submucosal dendritic cells and macrophages in the dome area of Peyer's patch (14). L. monocytogenes uses a pore-forming toxin, i.e. listeriolysin O encoded by hlyA, and caseinolytic proteins (Clp) to digest the phagosomal membrane and free themselves into the cytosol where they multiply extensively (15,16). The bacteria are disseminated via the lymphatic and blood circulatory systems to several tissues and organs, e.g. liver, spleen, and the central nervous system (17-20). Invasion of the brain results in massive infiltration of inflammatory cells into the tissue causing severe meningitis (21). Intercellular spread of L. monocytogenes is mediated by the surface-exposed actA protein which induces the formation of polarized actin filament, along which the bacteria move to the cell membrane to form a bulge-out structure called listeriopod (22,23). The bacteria are then engulfed by the adjacent cell into a double-membrane vacuole and exit to the cytosol using the listeriolysin O and other phospholipases (24,25).

Although agriculture and food production are the main occupations of Thai people, and agricultural products are the main export goods of the Kingdom, there is a paucity of information on the characteristics and virulence factors of L. monocytogenes which could be isolated from food items. Recently, we made a survey of pathogens in food samples in supermarkets and open markets in Bangkok and its periphery and found a certain prevalence of L. monocytogenes contamination (26). In this study, we isolated L. monocytogenes from raw meat samples collected from different markets in the Bangkok metropolitan area. We also investigated the pathogenic potential of the isolates by determining their virulence-associated genes. The isolates were genotyped and their ability to invade human epithelial cells and their antibiotic sensitivity were studied. To the best of our knowledge, this is the first study on molecular characterization and genotyping of L. …

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