On Microflora of Entomoparasitic Nematodes from Long-Tailed Souslik Fleas in Tuva Mountain Natural Plague Focus

Abstract

Entomoparasitic nematodes have a specific role to play in the persistence of Yersinia pestis in natural foci, however their natural microbial environment has not been studied.The aim of the study was to search for bacteria associated with nematodes parasitizing fleas-vectors of plague in the Tuva natural focus.Materials and methods. Fleas were collected during the planned epizootiological surveillance in May, 2017 and 2018. During the taxonomic identification of insects, the presence of parasitic nematodes was recorded. In 2017, bacteriological examination of fleas affected by nematodes and those free from them was carried out separately without dissection. The presence and number of bacteria colonies on the agar plates were taken into account. The results were evaluated by conventional methods using the Excel program. The t-criterion, one-factor analysis of variance were employed. In 2018, 84 invaded fleas were dissected. Extracted nematodes were suspended in Hottinger’s broth, followed by cultivation of grown bacteria on Hottinger’s agar. Systematic position of isolated cultures was determined through mass spectrometric analysis (MALDI-TOF) and partial sequencing of 16S rRNA.Results and discussion. In 2017, 30 samples of fleas with helminthes and 276 without helminthes were bacteriologically examined, including 23 samples infested and 145 non-infested specimens of the main vector, Citellophilus tesquorum. Statistical differences in the proportion of samples contaminated by unpretentious bacteria and effect of flea abundance in the sample on the number of colonies grown have not been revealed. In 2018, 26 cultures of bacteria of the genera Serratia, Staphylococcus, Pseudomonas, Acinetobacter, Macrococcus, and Bacillus were isolated from 23 samples of entomoparasitic nematodes. Possible ways of their penetration into flea imagoes are discussed.