[Relations of the causative agents of plague and listeriosis during their simultaneous stay in the flea Citellophilus tesquorum at different environmental temperatures].

Experiments were carried out to determine the persistence of a plague microbe with varying praline labeling (isolated in the Central Caucasian mountain focus of plague in the fleas Citellophilus tesquorum of a mountain subspecies) in the contamination of the mixed culture of the plague microbe and Listeria. Inoculation of fleas with a suspension of a plague microbe and Listeriae demonstrates the manifest signs of antagonism between both species of microorganisms. This is evidenced by the reductions in the time of cultivation and in the number ofthese bacterial species in the experimental group fleas co-infected with Yersinia pestis and Listeria monocytogenes as compared with the control fleas (infected with monocultures of the causative agents of plague and listeriosis). Inhibition of one bacterial population by another is pronounced temperature-dependent: + 4 degrees C is preferable for a proline-auxotrophic plague agent strain and environmental temperature elevation up to 18-20 degrees C ensures the preponderance of Listeria in C. tesquorum. Co-infection of fleas with plague bacteria and Listeria (which cannot be excluded in co-infections in mountain sousliks under natural conditions) may predict the suppressed vector activity of fleas and hence the limited circulation of the causative agent of plague by the rodent-flea-rodent scheme in the Central Caucasian mountain natural focus at an environmental temperature of + 18-20 degrees C.