Calcium Requirement and Virulence of Yersinia Enterocolitica

Abstract

At an optimal concentration of Mg highly virulent wild strains of Y. enterocolitica serotype O:8, with an LD50 for mice of < 103 cells i.v. had an in vitro requirement for Ca at 37.degree. C but not at 26.degree. C. Avirulent wild strains of Y. enterocolitica (LD50 > 107 cells i.v.) did not have this Ca dependence. When grown on Ca-depleted media at 37.degree. C, 8 highly virulent strains yielded 0.5-6% large Ca non-requiring avirulent colonies; the remaining colonies were slow growing, Ca-dependent and highly virulent. The Ca non-requiring mutants were quickly destroyed in organs within 48 h, even after large i.v. challenge. The slow-growing Ca-dependent colonies were highly virulent on i.v. inoculation, growing rapidly in the liver, spleen and lungs to produce multiple abscesses. Homogenates of heavily infected organs produced the original proportion of Ca non-requiring colonies when plated on media without Ca. A fluctuation test suggested that the emergence of Ca non-requiring mutants is the result of induction rather than spontaneous mutation.