Molecular Insights into Antibiotic-Resistant Escherichia coli from Unpasteurized Milk sold in Ohimini Local Government of Benue State, Nigeria

Abstract
Background:
The presence of pathogenic Escherichia coli in unpasteurised milk increases the danger of infection. This study investigates the prevalence, extended-spectrum beta-lactamase (ESBL) indicators, and antibiotic susceptibility of pathogenic E. coli in unpasteurised milk from the Ohimini Local Government Area in Benue State.
Methods:
One hundred milk samples were collected from the Ohimini Local Government Area, and E. coli isolates were identified through various methods including morphological, biochemical, serological analysis, and PCR. ESBL production was screened with the double-disc diffusion method, and β-lactamase genes (bla_TEM, bla_SHV, bla_CTX-M) were detected through simplex PCR. Antibiotic susceptibility was assessed using the Kirby–Bauer disc diffusion method against multiple antibiotics.
Findings:
13% of samples tested positive for E. coli, with 4(30.8%) classified as non-sorbitol fermenting (NSF) and 9(69.2%) as sorbitol fermenting (SF). All isolates were resistant to gentamicin. SF isolates showed significant resistance to ceftazidime 6(66.7%), aztreonam 4(44.4%), and amoxicillin–clavulanate (42%), but were less resistant to imipenem 1(11%) and other β-lactams. In contrast, NSF isolates exhibited higher resistance rates across multiple agents, with 3(75%) resistance to aztreonam, ceftazidime, and Augmentin, and 2(50%) resistance to ciprofloxacin and meropenem. All isolates were multidrug-resistant, and NSF isolates tested positive for at least one ESBL gene (bla-TEM, bla-SHV, or bla-CTX-M) when analyzed via PCR.
Conclusion:
Multidrug-resistant E. coli with ESBL genes detected in unpasteurized milk in Ohimini LGA emphasizes the necessity of mandatory pasteurization, enhanced dairy hygiene, and stricter veterinary antibiotic regulations to protect public health.