Epidemiological insights into virulence and antimicrobial resistance of Escherichia coli across dairy farms in Nagpur district

Antimicrobial-resistant Escherichia coli (E. coli) circulating across the human-animal-environmental interface is a major one-health concern. This study (April 2025-January 2026) investigated the occurrence, virulence, and antimicrobial resistance (AMR) patterns of E. coli across 558 samples comprising animal (n = 444), environmental (n = 80), and human (n = 34) sources collected from five organized dairy farms representing urban (n = 1), peri-urban (n = 2), and rural (n = 2) settings under a One Health framework. Samples were cultured for E. coli and E. coli O157, screened for Shiga-toxin genes (stx1, stx2) by polymerase chain reaction (PCR), and subjected to antimicrobial susceptibility testing and molecular detection of resistant genes. Overall, E. coli was detected in 70.06% of the samples, with the highest occurrence in environmental samples (78.75%), followed by animal (70.94%) and human (47.05%) samples, indicating a clear environmental predominance. In contrast, E. coli O157 was not detected in any of the samples. Virulence profiling revealed the presence of Shiga-toxin encoding genes stx1 (10.1%) and stx2 (13.7%), predominantly among animal isolates, with higher occurrence during monsoon and winter seasons. Antimicrobial susceptibility testing revealed high susceptibility to colistin (100%), tigecycline (97.2%), and carbapenems (>91%), while moderate resistance was observed against tetracycline (25.1%) and selected cephalosporins. Multidrug resistance (MDR) was identified in 18.02% of isolates, with an overall MAR index of 0.068. Molecular analysis showed a predominance of AmpC (33.25%), followed by tetA (20.05%), blaTEM (15.48%), blaCTX-M (12.18%), tetB (9.39%), and blaNDM (2.28%) genes, with notable seasonal variation. These findings indicate that the livestock ecosystem acts as a reservoir for resistant and potentially virulent E. coli, underscoring the need for integrated One Health AMR surveillance and targeted mitigation strategies.