[Increased invasiveness as one of the manifestations of phenotype variability of the plague microbe in fleas].

Experimental studies conducted on genetically connected virulent subcultures of Y. pestis showed that the death of albino mice infected by flea bite occurred earlier than in the animals infected by a syringe subcutaneously. A high invasiveness of Y. pestis subcultures isolated from fleas (in comparison with the initial strains and subcultures from the animals) persisted for 2--3 passages in their cultivation on artificial nutrient media.