[The variability of Yersinia pestis in the body of the flea].

Changes in the morphology and ultrastructure of Y.pestis cells at different periods of their stay in the body of fleas (Citellophilus tesquorum altaicus) have been studied. The study, carried out by means of optical and electron microscopy, as well as with the use of a culture medium for the isolation of L-forms, has revealed that in the body of fleas Y.pestis cells undergo the effect of processes leading to their L-transformation. As the result of L-transformation, the infective agent may take altered forms, including L-like variants. Such forms are retained in hungry insects and are capable of prolonged survival in the body of the carrier.