Enterochelin (enterobactin): virulence factor for Salmonella typhimurium

Abstract

The ability of S. typhimurium to synthesize enterochelin (ENT) affects its capacity to grow in vivo and in vitro. An ENT mutant (96-1) blocked in the conversion of chorismate to 2,3-dihydroxybenzoate was derived from SR-11, a strain of high mouse virulence. This mutant was unchanged in the other characteristics tested: colonial, biochemical, antigenic and cellular. In contrast to SR-11, growth of this mutant in complement-inactivated human serum was strongly inhibited. Addition of 5 .mu.M ENT to the cultures relieved their inhibition. Viable counts of bacteria injected into the mouse peritoneal cavity showed that without ENT, growth of 96-1 was inhibited markedly; with ENT, the apparent growth rate of 96-1 exceeded that of SR-11. The LD50 of 96-1 was 2-3 log units higher than that of SR-11. When ENT was injected, the ENT- mutant exhibited an ENT-dose-related decrease in its LD50. A single injection of 300 .mu.g of ENT per mouse with the inoculum reduced the LD50 of 96-1 to that of the wild-type strain. ENT may be a virulence factor for S. typhimurium.