Some galE mutants of Salmonella choleraesuis retain virulence.

galE mutants were isolated from three mouse-virulent strains of Salmonella choleraesuis (of group C1, O antigen 6,7) by selection for resistance to 2-deoxygalactose. The galE derivative of strain 381 comprised two components: galactose sensitive, thought to be the original mutant; and galactose resistant, presumably by a second mutation reducing galK or galT function or both. The galactose-sensitive component had an intraperitoneal 50% lethal dose for BALB/c mice of ca. 4 X 10(6) CFU, whereas the galactose-resistant component was about as virulent as its gal+ parent, with a 50% lethal dose of ca. 100 CFU. The galE mutant of strain 110 was somewhat sensitive to galactose, as shown by retardation of growth; its 50% lethal dose, ca. 500 CFU, was not much greater than the ca. 200 CFU value for its parent. The galE mutant of strain 117 showed the same partial sensitivity to galactose as strain 110 galE, but was nonvirulent (50% lethal dose of ca. 10(6) CFU versus ca. 400 CFU for its parent). Growth on galactose-supplemented medium restored the smooth phenotype, as indicated by phage sensitivity to three of the four galE strains, but only partially so for the strain 117 galE mutant. The retention of parental virulence by galE mutants of S. choleraesuis which are galactose resistant or somewhat galactose sensitive contrasts with the greatly reduced virulence of galactose-resistant galE mutants of Salmonella typhimurium and Salmonella typhi; this difference may result from the absence of galactose from the O repeat unit in the lipopolysaccharide of group C1 salmonellae.