Interaction of Listeria species with human cell monolayers

In foodborne listeriosis, the first step of infection must be attachment to, and invasion of, the gastrointestinal epithelium by virulent Listeria monocytogenes. Virulence factors affecting this invasion are only now being determined. We examined the interaction of L. monocytogenes, serotypes 4b and 1/2a strains with "smooth" and "rough" characteristics. In addition, flagellated and non-flagellated isogenic strains altered by transposon mutagenesis were examined to study the effect of flagellae on virulence. Strains of Listeria ivanovii and Listeria innocua were also studied. L. ivanovii demonstrated the greatest degree of internalization and L. innocua, the least. L. monocytogenes strains were intermediate and there were no significant differences between "rough" and "smooth" isolates. The presence or absence of flagellae did not effect cell association in this model. Minor differences between cell lines for the same strains were demonstrated. Variations in cell association for differing inocula temperatures (4 degrees, 22 degrees, 37 degrees) were also noted for all strains. The interaction of Listeria species with human cell monolayers appears to be complex. Hemolysin clearly play a significant role but other virulence factors may also be important.