HOMOLOGS OF THE SHIGELLA IPAB AND IPAC INVASINS ARE REQUIRED FOR SALMONELLA-TYPHIMURIUM ENTRY INTO CULTURED EPITHELIAL-CELLS

Entry into host cells is an essential feature in the pathogenicity of Salmonella spp. The inv locus of Salmonella typhimurium encodes severa l proteins which are components of a type III protein secretion system required for these organisms to gain access to host cells, We report here the identification of several proteins whose secretion into the c ulture supernatant of S. typhimurium is dependent on the function of t he inv-encoded translocation apparatus. Nucleotide sequence analysis o f the genes encoding two of these secreted proteins, SipB and SipC, in dicated that they are homologous to the Shigella sp. invasins IpaB and IpaC, respectively. An additional gene was identified, sicA, which en codes a protein homologous to IpgC, a Shigella protein that serves as a molecular chaperone for the invasins IpaB and IpaC. Nonpolar mutatio ns in sicA, sipB, and sipC rendered S. typhimurium unable to enter cul tured epithelial cells, indicating that these genes are required for b acterial internalization.