[Variants of Yersinia pestis resistant to a diagnostic bacteriophage and the problems related to them].

The data of literature on the pleiotropic variability of the resistance of Y. pestis mutants to diagnostic phage are presented. The conditions of reversion to the initial phenotype are characterized. The mechanisms of the appearance of such variability of Y. pestis, as well as problems arising in connection with this variability and linked with the pathogenic activity of Y. pestis, low effectiveness of the diagnostic methods used in the inspection of the natural foci of plaque, the reservation of microbes in nature during the periods between epidemics, are discussed.