Molecular Detection and Antimicrobial Resistance Patterns of Shiga Toxigenic Escherichia coli Isolated from Bovine Subclinical Mastitis Milk Samples in Kurdistan, Iran

Bovine subclinical mastitis is regarded as a devastating disease due to the economic costs imposed on dairy husbandry. Moreover, it is a hazard in the public sector in the cases of zoonotic bacteria because of the potential role of unpasteurized milk and dairy products to propagate the infectious agent to the human food chain. The present study aimed to evaluate the frequency, virulence content, and antimicrobial resistance profile of Shiga toxin-producing Escherichia coli (STEC) strains isolated from bovine subclinical mastitis in Kurdistan Province, West of Iran. A total of ۴۰۰ bovine subclinical mastitis milk samples recognized in the California Mastitis Test were collected aseptically and analyzed for the presence of E. coli phenotypically and molecularly. The isolates were genotypically screened for stx۱, stx۲, and eae genes. Furthermore, O۱۵۷:H۷ STEC strain was searched among the isolates in a duplex polymerase chain reaction. The antimicrobial resistance scheme of the isolates was determined using the agar disk diffusion method. In general, ۱۷۳ (۴۳.۲۵%) E. coli isolates were detected among which ۳۹ (۲۲.۵۴%) isolates were STEC. The frequency of STEC virulence genotypes was stx۲ (۲۵ isolates, ۶۴.۱۰%), stx۲+eae (۶ isolates, ۱۵.۳۸%), stx۱+stx۲ (۶ isolates, ۱۵.۳۸%), and stx۱+stx۲+eae (۲ isolates, ۵.۱۲%). In addition, three O۱۵۷: H۷ strains were identified with the genetic content of stx۱+stx۲+eae (۲ isolates) and stx۱+stx۲ (۱ isolate). The most prevalent antimicrobial resistance was observed against streptomycin, tetracycline, and ampicillin. Gentamycin, amoxicillin-clavulanic acid, and trimethoprim-sulfadiazine were the most effective antibiotics against O۱۵۷ strains, whereas gentamycin, ciprofloxacin, and nitrofurantoin were effective against non-O۱۵۷ strains. The results revealed the significant role of STEC in bovine subclinical mastitis in the studied region. In addition, the distribution of O۱۵۷:H۷ strain and high prevalence of multidrug resistance among the isolates is a matter of concern. Therefore, there is a potential threat of human infection following the consumption of contaminated milk with STEC in Kurdistan Province, Iran.