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Effects of Psa and F1 on the Adhesive and Invasive Interactions of Yersinia pestis with Human Respiratory Tract Epithelial Cells

Fengzhi Liu, Huaiqing Chen, Estela M. Galván, Melissa A. Lasaro, and Dieter M. Schifferli^*

Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, 3800 Spruce Street, Philadelphia, Pennsylvania 19104

Received 14 April 2006/ Returned for modification 13 June 2006/ Accepted 12 July 2006

Yersinia pestis, the causative agent of plague, expresses the Psa fimbriae (pH 6 antigen) in vitro and in vivo. To evaluate the potential virulence properties of Psa for pneumonic plague, an Escherichia coli strain expressing Psa was engineered and shown to adhere to three types of human respiratory tract epithelial cells. Psa binding specificity was confirmed with Psa-coated polystyrene beads and by inhibition assays. Individual Y. pestis cells were found to be able to express the capsular antigen fraction 1 (F1) concomitantly with Psa on their surface when analyzed by flow cytometry. To better evaluate the separate effects of F1 and Psa on the adhesive and invasive properties of Y. pestis, isogenic caf (F1 genes), psa, and caf psa mutants were constructed and studied with the three respiratory tract epithelial cells. The psa mutant bound significantly less to all three epithelial cells compared to the parental wild-type strain and the caf and caf psa mutants, indicating that Psa acts as an adhesin for respiratory tract epithelial cells. An antiadhesive effect of F1 was clearly detectable only in the absence of Psa, underlining the dominance of the Psa⁺ phenotype. Both F1 and Psa inhibited the intracellular uptake of Y. pestis. Thus, F1 inhibits bacterial uptake by inhibiting bacterial adhesion to epithelial cells, whereas Psa seems to block bacterial uptake by interacting with a host receptor that doesn't direct internalization. The caf psa double mutant bound and invaded all three epithelial cell types well, revealing the presence of an undefined adhesin(s) and invasin(s).

Editor: V. J. DiRita

F.L., H.C., and E.M.G. are co-first authors who contributed equally to this work.

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