Yersinia pestis: correlation of ultrastructures and immunological status.

Ultrastructural identification and localization of the fraction 1 "envelope" antigen in the plague bacillus Yersinia pestis were the primary objectives of this brief study. The antigenicity of extra-cellular material between the bacilli in undisturbed cultured colonies and that of the pathogen per se were measured and correlated by means of the semi quantitative complement fixation method after incubation for 72 h at 37 C. When the amount of extracellular substance in wild-type T1 (virulent) bacteria was compared by electron microscopy with that in avirulent strains of Y. pestis, with and without passage through guinea pigs, we found that the material of interest was greatly attenuated or even absent in colonies that had not been passed through animals, whereas passage markedly augmented production of the material. We also explored the requirement for larger quantities of Ca(2+) and Mg(2+) in the culture media and discovered that without these ions production of the extracellular material was limited. These observations support the hypothesis that this extracellular substance between cultured Y. pestis bacilli of various strains represents the source of the fraction 1 envelope antigen.