An analysis of Mycoplasma mycoides by in vivo methods.

Fresh isolates of the small colony (SC) type of Mycoplasma mycoides subsp. mycoides readily produced mycoplasmaemia in mice inoculated i.p. The mycoplasmaemic capability of large colony (LC) strains was much less by comparison. Cross-immunization and -hyperimmunization tests in mice were made by injecting vaccines i.v., challenging i.p., and assessing the results on the presence or absence of mycoplasmaemia at daily intervals thereafter, as demonstrated by tail-blood culture in a selective medium. In terms of mouse-protective antigens, the SC and LC types were related but not identical. SC strains, unlike LC strains, were homogeneous. The SC and LC types differed from M. mycoides subsp. capri but were nonetheless related to it, the former less closely than the latter. Cross-immunization by M. mycoides subsp. mycoides (SC and LC types) against M. mycoides subsp. capri was often, but not always, unidirectional.