A role for Salmonella fimbriae in intraperitoneal infections

Enteric bacteria possess multiple fimbriae, many of which play critical rol es in attachment to epithelial cell surfaces. SEF14 fimbriae are only found in Salmonella enterica serovar Enteritidis (S. enteritidis) and closely re lated serovars, suggesting that SEF14 fimbriae may affect serovar-specific virulence traits. Despite evidence that SEF14 fimbriae are expressed by 5. enteritidis in vivo, previous studies showed that SEF14 fimbriae do not med iate adhesion to the intestinal epithelium. Therefore, we tested whether SE F14 fimbriae are required for virulence at a stage in infection after the b acteria have passed the intestinal barrier. Polar mutations that disrupt th e entire sef operon decreased virulence in mice more than 1,000-fold. Nonpo lar mutations that disrupted sefA (encoding the major structural subunit) d id not affect virulence, but mutations that disrupted sefD (encoding the pu tative adhesion subunit) resulted in a severe virulence defect. The results indicate that the putative SEF14 adhesion subunit is specifically required for a stage of the infection subsequent to transit across the intestinal b arrier. Therefore, we tested whether SefD is required for uptake or surviva l in macrophages. The majority of wild-type bacteria were detected inside m acrophages soon after i.p. infection, but the sefD mutants were not readily internalized by peritoneal macrophages, These results indicate that the po tential SEF14 adhesion subunit is essential for efficient uptake or surviva l of 5. enteritidis in macrophages. This report describes a role of fimbria e in intracellular infection, and indicates that fimbriae may be required f or systemic infections at stages beyond the initial colonization of host ep ithelial surfaces.