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The ail gene of Yersinia enterocolitica has a role in the ability of the organism to survive serum killing

Two Yersinia enterocolitica genes, inv and ail, play a major role in the ability of this microorganism to enter cultured mammalian cells. ail-homologous sequences are present only in pathogenic species and strains of Yersinia. We previously demonstrated (D. E. Pierson and S. Falkow, Infect. Immun. 58:1059-1064, 1990) that four different nonpathogenic isolates of Y. enterocolitica are not able to invade tissue culture cells because they contain functionally inactive variants of the inv gene. When a functional version was introduced into these strains, they became invasive. In this study, we introduced a functional ail gene into the same strains and found that the ail gene was expressed but that these strains neither adhere to nor invade cultured animal cells. However, these recombinant strains became resistant to killing by human serum, whereas their parental strains were not. Using an ail mutant, we also demonstrate that the ail gene has a role in both invasion/adherence and serum resistance in a pathogenic isolate of Y. enterocolitica. These results support a role for Ail in the pathogenesis of Y. enterocolitica infection and disease.