Phenotypic and genotypic characteristics of Escherichia coli from cattle in dairy farms in Chittagong

Abstract

A cross-sectional survey was conducted to assess the diversity among fecal Escherichia coli from cattle in the dairy farms of Chittagong region. A total of 21 farms were selected and swabs were collected from recto anal junctions (RAJ) of randomly selected 419 cattle on them. The diversity of E. coli, particularly those belonging to probable entero hemorrhagic E coli (EHEC) O157 serogroup was discriminated from others based on observation of sorbitol non-fermenting colonies of a selective medium named potassium tellurite added sorbitol MacConkey (CT-SMAC) agar. Any member of the EHEC O157 serogroup is sorbitol non-fermenter and thus produces colorless colonies. E. coli fidelity on four selected isolates was tested for the presence of seven house-keeping genes, and their genetic diversities were verified by plasmid profiling and pulsed field gel electrophoresis (PFGE). Finally, their antimicrobial susceptibility profiles were also assessed by disk-diffusion method, against 11 antimicrobials. The results showed that all the 21 cattle farms were positive for probable EHEC O157, but the magnitude of colonized animals with it varied from farm to farm. The overall prevalence of probable EHEC was 7.6% (32/419) (95% CI 4.3-12.7%) and its prevalence in the adult cows, heifers and calves were 6.4% (95% CI 0.07-11.9%), 9% (95% CI 0.01-14.6%) and 10% (95% CI 6.4-24.6%), respectively. Its prevalence in the cows suffering from mastitis (2.4%) was 0.29 (95% CI 0.12-0.86) times lower compared with others (P=0.015). The population of probable EHEC O157 in the dairy cattle in Chittagong seemed genetically diverse based on plasmid and PFGE profiles of four selected isolates. The antimicrobial resistance profiles of the probable EHEC isolates varied substantially. Most EHEC O157 isolates showed diversity in their resistance patterns against 11 antimicrobials tested. O-serotypic identities of the probable EHEC O157 isolates need to be confirmed by the rfb gene or serogroup-specific agglutination test and the possession of the virulent genes, such as stx1, stx2, eae and HlyA in them also remain unexplored from the study.