Multiple-Drug Resistant Shiga Toxin-Producing E. coli in Raw Milk of Dairy Bovine

Introduction: Raw milk may contain pathogenic microorganisms harmful to humans, e.g., multidrug-resistant Escherichia coli non-O157:H7, which can cause severe colitis, hemolytic uremia, and meningitis in children. No studies are available on the prevalence of Shiga toxin-producing E. coli (STEC O157:H7) in sick or healthy dairy animals in the Khyber Pakhtunkhwa Province of Pakistan. Aim: This study aimed to isolate, characterize, and detect antibiotic resistance in STEC non-O157:H7 from unpasteurized milk of dairy bovines in this province. Materials and Methods: We collected raw milk samples (n = 800) from dairy farms, street vendors, and milk shops from different parts of the Khyber Pakhtunkhwa Province. E. coli was isolated from these samples followed by latex agglutination tests for serotyping. The detection of STEC was conducted phenotypically and confirmed by the detection of virulence genes genotypically. An antibiogram of STEC isolates was performed against 12 antibiotics using the disc diffusion method. Results: A total of 321 (40.12%) samples were found to be positive for E. coli in this study. These samples were processed for the presence of four virulence genes (Stx1, Stx2, ehxA, eae). Forty samples (5.0%) were STEC-positive. Of these, 38%, 25%, 19%, and 18% were positive for Stx1, Stx2, ehxA, and eae, respectively. Genotypically, we found that 1.37% of STEC isolates produced extended-spectrum beta-lactamase (ESBL) and contained the blaCTX M gene. Resistance to various antibiotics ranged from 18% to 77%. Conclusion: This study highlights the risk of virulent and multidrug-resistant STEC non-O157:H7 in raw milk and the need for proper quality surveillance and assurance plans to mitigate the potential public health threat.