[Current data on the polymorphism of Rickettsia prowazekii and burneti in cultured cells]

In cultivation of Rickettsia prowazeki (strains Breinl and E) in the cell cultures of guinea pig kidneys (GPK) and chick embryo fibroblasts (CEF) ultrastructure of rickettsia of unusual shape (filamentous, irregularpleomorphic and spheroplast-like) were revealed along with rickettsia of the usual shape and size. The polymorphism was less pronounced in the GPK and the CEF cells of Rickettsia burneti (strain M-44). It is supposed that rickettsial polymorphism was not associated with their developmental cycle and served as a morphological expression of the changes in the microorganism under the effect of unfavourable ecological conditions. The appearance of filamentous forms could be associated with disturbed cell division process; changed rigidity of the cell wall could serve as the cause of appearance of pleomorphic rickettsia. In difference from polymorphism, the cycle of rickettsial development is considered to be (in the basis of modern electron microscopic data) as a biological replacement of the vegetative (rod-like, bacillary) forms by those more stable in the external environment, resting (coccoid).