Research Institute for Plague Control of Siberia and Far East, Irkutsk, Russia
The study of the specific features of adaptation of different Y.pseudotuberculosis plasmid variants to the soils of the southern and north-western anthropurgic foci of pseudotuberculosis in the Irkutsk region was made. In these foci, respectively, the two-plasmid and single-plasmid variants of the infective agent were found to circulate. The study revealed that strain 47:82 MD showed selective adaptability to the conditions of soil ecosystem: for this strain the gray forest soil of its “own” focus in combination with a temperature of 18—22°C was more preferable. The main mechanism of adaptation was the formation of uncultivable forms of microorganisms and the maintenance of their great numbers and virulence. On the contrary, in turf carbonate soil at a temperature of 4—8°C the populations of single-plasmid microbial cells survived longer and at higher concentrations, and irrespective of their plasmid profile (47; 82:47; 82:47:7.5:2.7 MD), the two-phase adaptation cycle could be observed: (1) the loss of plasmid pYV47 and the multiplication of avirulent clones, (2) a decrease in the concentration of microorganisms and the preservation of their virulence.
Zh. Mikrobiol. (Moscow), 2003, No. 6, P. 37—41