Cattle colibacillosis in Perm krai: prevalence, sources of the causative agent and its biological characterization

Infectious diseases in agricultural enterprises of the Russian Federation are annually recorded in 50 % of the livestock, while the death of young calves during the first weeks of life ranges from 14 to 60 %. Colibacillosis remains the main infectious pathology in terms of morbidity and mortality, despite the widespread use of modern antibiotics and vaccines. To assess the prevalence of colibacillosis among cattle and identify the source of the infectious agent, for the first time an integrated approach was used covering a triad of sick animals-healthy animals-environment, which is of theoretical significance because it contributes to a better understanding the patterns of the epizootic process. An important practical aspect of the work was the analysis of data from long-term sanitary and zoo-hygienic records, which indicates that the control of the risk of Escherichia coli infections should be aimed not only at the natural reservoirs but also at the environment factors. The purpose of the study was to assess the prevalence of colibacillosis in cattle in various agricultural enterprises of the Perm Territory and to study the biological properties of the pathogen. To assess the Escherichia coli contamination of inventory, feeding and watering systems, data from sanitary and zoo-hygienic studies were analyzed. The incidence of the infections in cattle was summarized based on the reports from the Perm Veterinary Diagnostic Center, the livestock department of the Ministry of Agriculture of the Perm Krai for 2010-2020, statistical data from the Department of Veterinary Medicine of the Perm Krai and form laboratory records. The reports also covered bacteriological data for 22,480 samples from beef and dairy farms ( n = 146). Sanitary and zoo-hygienic analyses of swabs from dairy equipment, inventory of slaughterhouses, feed of plant and animal origin, mixed feed were carried out for 29,207 samples from the same farms. The antigenic structure of the E. coli isolates was determined. The sensitivity of strains to antibacterial drugs was assayed by disk diffusion method (ampicillin 10 µg, cefoxitin 30 µg, ceftriaxone 30 µg, cefepime 30 µg, meropenem 10 µg, imipenem 10 µg, aztreonam 30 µg, amikacin 30 µg, gentamicin 10 µg, ciprofloxacin 5 µg, levofloxacin 5 µg, moxifloxacin 5 µg, tetracycline 30 µg, chloramphenicol 30 µg). In a prospective study (2020-2021), the prevalence of Shiga toxin-producing E. coli (STEC) strains in a population of healthy animals was assessed. Cultures ( n = 61) were isolated from cattle feces. Genes encoding Shiga toxins 1 and 2 ( stx1 and stx2 ) were detected by polymerase chain reaction at the end point. The research results indicate that in recent years the prevalence of colibacillosis in the Perm Krai does not exceed 20 %. An increased number of dead animals and sick animals with diarrheal syndrome corresponded to a decreased immunization of pregnant cows. There were sporadic cases of the disease, but the risk of horizontal transmission of the pathogen, including through environmental objects, was high. E. coli was mostly isolated from swabs from dairy equipment and inventory of slaughterhouses, as well as from animal feed. Five most epizootically significant serogroups were identified, the E. coli O8, O15, O20, O101, and O115; in rare cases, E. coli O157 was isolated. The antibiotic resistance profiles of E. coli strains isolated from sick, dead and healthy animals did not differ significantly, except for tetracycline and chloramphenicol, resistance to which was significantly higher in E. coli strains of the first group. Of note is the higher proportion of cultures resistant to ampicillin and ciprofloxacin in the E. coli subpopulation from healthy cattle. In addition, the stx1 (2.0 %) and stx2 (6.1 %) genes were found in E. coli from healthy cattle. That is, our data confirm that pathogens can persist in the gastrointestinal tract of both sick and healthy farm animals, which become the source of STEC. Additional sources of E. coli infection, including STEC strains, are drinking water, feed, and other abiotic components.