[The possibility of preserving the causative agent of plague in soil in resting (nonculturable) form].
The parallel study of soil specimens from the burrows of great gerbils, taken in the natural focus of infection at the period between epidemics, by the bacteriological method and with the use of polymerase chain reaction (PCR) demonstrated that, simultaneously with the negative results of inoculations into nutrient media, PCR revealed the presence of Y. pestis in 4 out of 72 soil specimens. The serological study (in the indirect hemagglutination test) revealed the presence of Y. pestis capsular antigen (fraction l) in 16 out of 75 soil specimens. The transition of Y. pestis (strain EV) into the nonculturable state was experimentally shown in sterile soil extract and in association with protozoa, algae and Euglena. Bacteriologically detected Y. pestis disappeared or were represented by a few cells after day 7, while PCR could register the presence of Y. pestis at a concentration of 10(4)-10(5) microbial cells per ml until the end of the term of observation (30 days). After the enrichment of the nutrient medium with fetal serum the complete reversion of Y. pestis nonculturable forms was observed: the concentration of bacteria grown on agar was 10(5) colony-forming units per ml. Transition into the nonculturable state was also observed in distilled water. The results of this investigation are discussed with special emphasis to the possibility of the preservation of Y. pestis in the nonculturable from during the period between epidemics as applied to the problem of plague epizootic.