Molecular Insights Into the Phylogenetic Diversity, Virulence Determinants, and Antimicrobial Resistance Pattern of Escherichia coli From Milk of Mastitis-Affected Cows.

This study examined the prevalence, molecular characterization, and antimicrobial resistance of Escherichia coli associated with the bovine clinical mastitis in the northern part of Bangladesh. A total of 120 milk samples from infected cows in Dinajpur, Thakurgaon, and Nilphamari were collected. General bacteriological and biochemical tests were conducted to isolate and identify the bacteria. In addition, PCR assays were performed to molecularly detect and identify virulence and antibiotic resistance genes. Bacteriological, biochemical, and molecular methods confirmed the presence of E. coli, which constituted a total prevalence of 35.0%. Phylogenetic typing revealed two types, A1 (81.0%), and B2 (19.0%) (p < 0.001), suggesting that commensal strains predominating the total E. coli population. Virulence gene (eae, stx1, and stx2) screening was negative, indicating a lack of classical enteropathogenic/enterohemorrhagic characteristics. Antibiotic susceptibility testing showed that the level of antibiotic resistance was high, especially to ampicillin (100.0%), amoxicillin (92.86%), tetracycline (73.81%), erythromycin (61.91%), streptomycin (59.53%), and gentamicin (52.38%). The isolates were mostly sensitive to ceftriaxone (85.71%) and moderately sensitive to chloramphenicol and ciprofloxacin. The most abundant resistance gene was tetA (85.71%), followed by sul2 (59.52%), blaTEM (57.14%), aadA1 (50.0%), qnr (23.80%), and blaCTX-M (19.04%) (p < 0.001), which are strongly connected to the phenotypic resistance pattern. In general, the results indicate that highly resistant E. coli are prevalent in the case of bovine mastitis, which highlights the necessity to use antibiotics reasonably, conduct more frequent monitoring, and use biosecurity to limit the spread of resistant pathogens in the dairy industry, as well as the environment.