Ecological Bases of Yersinia pestis Variability in the Nature

The natural plague focus is a complex dynamic biological system that ensures the existence of Yersinia pestis in time and space at the ecological level. Natural plague foci in Asia and Europe demonstrate the discrete character of Y. pestis populations and bespeak a powerful selection factor. Atypical strains isolation illustrates natural variability processes in foci; nevertheless, establishment and propagation of new forms are affected by selection eliminating most of the new variants, specifically those with reduced virulence. Only Y. pestis populations may exist due to selective advantage or unique environment. Selective advantages may include varying needs in growth factors noted in Y. pestis strains from different foci. Our experiments identified the dependence of Y. pestis growth on the number of amino acids in solid media. Quantitative differences were found in free amino acids in Rhombomys opimus blood sera from different regions of Central Asian desert plague focus. The plague infection process features interaction between bacteria and carrier’s phagocytes, contingent upon the intracellular character of Y. pestis parasitism. Specific sensitivity of animals to Y. pestis is driven by a genetically determined level of phagocytising cells’ antimicrobial potential. The critical role is played by the oxygen-dependent cytocide system of phagocytes. Its activity level relies upon the functional status of neutrophils and macrophages.