Invasion of epithelial cells by Yersinia pestis: Evidence for a Y pestis-specific invasin

The causative agent of plague, Yersinia pestis, is regarded as being noninv asive for epithelial cells and lacks the major adhesins and invasins of its enteropathogenic relatives Yersinia enterocolitica and Yersinia pseudotube rculosis. However, there are studies indicating that Y. pestis invades and causes systemic infection from ingestive and aerogenic routes of infection. Accordingly, we developed a gentamicin protection assay and reexamined inv asiveness of Y. pestis for HeLa cells. By optimizing this assay, we discove red that Y. pestis is highly invasive. Several factors, including the prese nce of fetal bovine serum, the configuration of the tissue culture plate, t he temperature at which the bacteria are grown, and the presence of the pla sminogen activator protease Pla-encoding plasmid pPCP1, were found to influ ence invasiveness strongly. Suboptimal combinations of these factors may ha ve contributed to negative findings by previous studies attempting to demon strate invasion by Y. pestis. Invasion of HeLa cells was strongly inhibited by cytochalasin D and modestly inhibited by colchicine, indicating strong and modest respective requirements for microfilaments and microtubules. We found no significant effect of the iron status of yersiniae or of the pigme ntation locus on invasion and likewise no significant effect of the Yops re gulon. However, an unidentified thermally induced property (possibly the Y. pestis-specific capsular protein Caf1) did inhibit invasiveness significan tly, and the plasmid pPCP1, unique to Y. pestis, was essential for highly e fficient invasion, pPCP1 encodes an invasion-promoting factor and not just an adhesin, because Y. pestis lacking this plasmid still adhered to HeLa ce lls. These studies have enlarged our picture of Y. pestis biology and revea led the importance of properties that are unique to Y. pestis.