LISTERIA-MONOCYTOGENES - ASPECTS OF PATHOGENICITY

The genus Listeria includes different species of ubiquitary present gr am-positive rod shaped bacteria. The species Listeria monocytogenes ca uses severe diseases like meningitis and meningoencephalitis in humans . Additional groups of syndroms associated with this microorganism are the listeriosis of the pregnant woman, mostly appearing as an abortio n or septic premature birth and the meningitis of the newborn. Transmi ssion of Listeria may occur on the oral route due to infected food lik e raw milk and cheese, raw meat or soil contaminated food like prepack ed salads, respectively. The understanding of Listeria virulence was i mproved by different investigations employing cell cultures and molecu lar methods like knockout of genes encoding potential virulence factor s. Nowadays the procedure of infection of cells is divided in four dif ferent parts : internalisation, escape from intracellular vacuole, nuc leation of actin filaments and cell-to-cell spread. So called Internal ins are produced by Listeria and are obviously needed for cell invasio n. Listeria could escape intracellular vacuoles producing a hemolysin, Listeriolysin O, and proliferate inside the host cells. The surface b ounded protein Actin A mediates the contact to the actin filament syst em of the host cell. This is important for the intracellular spread of Listeria. In the next step a cell-to-cell spread supported by phospho lipase and lecithinase occurs. Despite the high incidence of contamina ted food only a little incidence of listeriosis is observed. This may be explained in an indirect vaccination due to less virulent strains. However, the immune response of patients even with well documented lis teriosis may be poor and causes false negative serological results som etimes. In this paper the know virulence factors of the interesting sp ecies L. monocytogenes are demonstrated and the course of infection is discussed.