Mutants of Group D 1 Salmonella Carrying the Somatic Antigen of Group A Organisms: Isolation and Serological Characterization

O antigen mutants were obtained from Salmonella durban , a group D 1 organism, by treatment with N -methyl- N′ -nitro- N -nitrosoguanidine. Serological studies demonstrated that the mutants lost the O-9 antigen factor of the parent organism but acquired the O-2 factor specific to group A Salmonella . Lipopolysaccharides of the mutant strains contained paratose which determines the specificity of O-2 factor. Tyvelose, present in the wild-type lipopolysaccharide, was not found in the mutants. H antigens and other biological characteristics of the mutant strains were the same as those of the wild-type organism. The present finding implies that group A Salmonella species might be derived from group D 1 organisms.