Effect of enterobacterial common antigen on mouse virulence of Salmonella typhimurium.

A series of nearly isogenic O4-12, and O-6,7 Salmonella typhimurium strains differing in regard to the enterobacterial common antigen (ECA) were constructed by conjugation. When tested in intraperitoneal infection of mice, the O-4,12 strains containing ECA were more virulent than their O-4,12 sister recombinants without ECA (P = less than 0.001). The same difference could be shown with ECA-positive and ECA-negative S. typhimurium derivatives, whose O antigens were of the group C type (O-6,7). The ECA-positive and ECA-negative O-4,12 strains did not differ in their growth rates in broth or clearance rates in vivo.