Dissociation in Pasteurella pestis: interrelations of smooth and nonsmooth variants.

Dissociation indices of Pasteurella pestis strains. Observations on viable cell numbers and the morphology of colonies isolated from suspensions of P. pestis strains Poona, 139L, 53,2 and 623 were made by the method described by Eisler et al. (1958). Generation time studies. Subcultures of smooth and nonsmooth colonial variants were made in 100-ml amounts of heart infusion broth (HIB, Difco) which was aerated by shaking at 230 strokes per minute on a reciprocal shaker at 28 C. Generation times were determined by the method of WVilson and Miles (1946) as applied to viable cell numbers only. A cell division factor of 2 was assumed since relative rather than absolute values were required. Serological comparisons. Serological comparisons of dissociants were made in Ouchterlony gel diffusion plates prepared as described by Crumpton and Davies (1956). The antigens were concentrated viable suspensions of smooth or nonsmooth colonies picked from the surfaces of