TAILIEUCHUNG - Chapter 132. Infections Caused by Listeria monocytogenes

Listeria monocytogenes is a food-borne pathogen that can cause serious infections, particularly in pregnant women and immunocompromised individuals. A ubiquitous saprophytic environmental bacterium, L. monocytogenes is also a pathogen with a broad host range. Humans are probably accidental hosts for this microorganism. L. monocytogenes is of interest not only to clinicians but also to basic scientists as a model intracellular pathogen that is used to study basic mechanisms of microbial pathogenesis and host immunity. . | Chapter 132. Infections Caused by Listeria monocytogenes Listeria monocytogenes is a food-borne pathogen that can cause serious infections particularly in pregnant women and immunocompromised individuals. A ubiquitous saprophytic environmental bacterium L. monocytogenes is also a pathogen with a broad host range. Humans are probably accidental hosts for this microorganism. L. monocytogenes is of interest not only to clinicians but also to basic scientists as a model intracellular pathogen that is used to study basic mechanisms of microbial pathogenesis and host immunity. Microbiology L. monocytogenes is a facultatively anaerobic nonsporulating grampositive rod that grows over a broad temperature range including refrigeration temperatures. This organism is motile during growth at low temperatures but much less so at 37 C. The vast majority of cases of human listerial disease can be traced to serotypes 1 2a 1 2b and 4. L. monocytogenes is weakly p-hemolytic on blood agar and as detailed below its p-hemolysin is an essential determinant of its pathogenicity. Pathogenesis Infections with L. monocytogenes follow ingestion of contaminated food that contains the bacteria at high concentrations. The conversion from environmental saprophyte to a pathogen involves the coordinate regulation of bacterial determinants of pathogenesis that mediate entry into cells intracellular growth and cell-to-cell spread. One essential determinant of L. monocytogenes pathogenesis is the transcriptional activator PrfA which activates the majority of genes required for cell entry and intracellular parasitism. Many of the organism s pathogenic strategies can be examined experimentally in tissue culture models of infection such a model is presented in Fig. 132-1. Like other enteric pathogens L. monocytogenes induces its own internalization by cells that are not normally phagocytic. Its entry into cells is mediated by host surface proteins classified as internalins. Internalin-mediated entry is .

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