MOUSE VIRULENCE OF SALMONELLA

Salmonella typhimurium derivatives with either the original group B-type O antigens 1, 4, (5,) 12 or the transduced group D-type O antigens 1, 9, 12 have been previously shown to have different LD50 doses in intraperitoneal infection of the mouse, so that the 1, 4, (5,) 12 derivatives are more virulent than the 1, 9, 12 derivatives. The strains compared differed from each others in only a small part of their chromosome including the rfb cluster, which determines the O antigen specificity. We have now investigated a possible immunological basis of this difference by comparing the same strains as pathogens in thymectomized, X-irradiated mice. Although the LD50 doses were much reduced by the treatment, the difference between the 1, 4, (5,) 12 and the 1, 9, 12 strains was retained. No antibodies towards either type of bacteria were demonstrable in the uninfected mice.