Comparative virulence properties of epizootic strains of <i>Escherichia coli</i> bacteria

Abstract

The results of the study to determine the virulence of production strains and epizootic isolates of Escherichia coli isolated in the Moscow and Tula regions in livestock farms and in the private sector from 2016 to 2022 are presented. In the experiment, the virulence of Escherichia coli was studied by determining the LD50 of Escherichia coli isolates for biological test systems. The most virulent strain from the museum collection was E. coli No. TP-85; the most avirulent were E. coli No. 727 and E. coli No. D616. The isolates selected by us showed the following results: the most virulent were E. coli 22/20, E. coli 3/16, E. сoli 20/20, E. coli 24/21 – E. coli 7/16, E. coli 19/2, E. coli 18/20, E. coli 9/17, E. coli 5/16, E. coli 28/21, E. coli 29/21. Avirulent were the isolates E. coli 25/21 and E. coli 17/20. LD50 for them was 22,36 × 108. The study of museum strains of E. coli isolates compared with the isolates obtained in the Moscow and Tula regions led to the conclusion that during long-term storage of collection strains, their virulence decreases. The tendency of strains to lose their physicochemical properties (stability) during lyophilization has also been noted. There could be several reasons for this: imperfect control and storage at different stages of the culture life cycle; improper lyophilization drying when strains were not deep-frozen; and failure to follow drying steps, which over time led to a change in the genetic structure of the strain.