[An increase in the virulence of Yersinia pestis bacteria when the cells are incubated in hemolyzed human erythrocytes].

The incubation of Y. pestis, the causative agent of plague, in hemolyzed human red blood cells at 37 degrees C for 3 hours enhanced the virulence of vaccine strain EV76 in white mice and guinea pigs and decreased the LD50 of attenuated strains. The phenomenon of increased virulence has been observed only in case of the combined injection of bacteria with the incubation medium. The virulence of Y. pestis cells, introduced alone after such treatment, has proved to remain at the same level.