INFLUENCE OF YERSINIA PESTIS PLASMID CONTENT ON BIOFILM FORMATION IN FLEAS WITH DIFFERENT VECTOR ACTIVITY

Abstract

Aim. Influence of the plague agent plasmid content on biofilm formation in vivo and death rate of fleas-vectors with different vector activity in experiment were analyzed. Materials and methods. Three Yersinia pestis strains: virulent I-3230 (pYT, pYV, pYP) and I-2638 (pYT, pYV, pYP, pTP 33), and its selected avirulent isogenic clone I-3480 lacking two plasmids (pYV, pYP) were used. Three species of fleas were artificially infected: 477 individuals of Xenopsylla cheopis (a highly active vector), 441 - Citellophilus tesquorum (an active vector), 519 - Frontopsylla lucu-lenta (a low-active vector). The peculiarities of Y. pestis biofilm formation in fleas were estimated by a portion of individuals with bacterial «conglomerates» and «blocks» for a feeding. Death rate of the insects was defined by the percent of the dead fleas at each feeding. Results. All three flea species infected by Y. pestis strains carrying an additional plasmid pTP33 (I-2638 and I-3480) demonstrated the increase of the individual number with various biofilm forms in comparison with the three-plasmid strain I-3230. In X. cheopis it occurred due to the blocked insects, in C. tesquo-rum - mainly due to the fleas containing «conglomerates», in F. luculenta it was completely connected with ectoparasites with «conglomerates». A share of X. cheopis and C. tesquorum died at a feeding was higher in ectoparasites infected with I-3230 strain and F. luculenta - infected by I-2638. Conclusion. Y. pestis strains possessing an additional replicon pTP33 formed a biofilm in the infected insects more often and larger size than a classical three-plasmid variant. Influence of the strain plasmid content on death rate of the infected fleas depended on a vector species.