Prevalence, antimicrobial resistance and biofilm forming ability of Escherichia coli in milk, animal handlers and slurry samples from dairy herds of Punjab, India

Antimicrobial-resistant <i>Escherichia coli</i> serves as an indicator for monitoring the occurrence of antimicrobial resistance (AMR) at the human, animal, and environmental interface. The present study employs a 'One Health' framework to determine the prevalence, phenotypic and genotypic characterisation of the AMR profile and biofilm forming ability of <i>E. coli</i> isolates from milk, hand swabs and slurry samples of 405 dairy herds in Punjab, India. An overall prevalence of <i>E. coli</i> was 34.3% (139/405) (95% CI: 0.30 to 0.39) from pooled milk samples, 9.1% (37/405) (95% CI: 0.06 to 0.12) from the hand swabs of animal handlers and 64.4% (261/405) (95% CI: 0.60 to 0.69) in the slurry samples. Multidrug resistance (resistance to 3 or more classes of antimicrobials) was exhibited by 24.4% (34/139) of <i>E. coli</i> isolates from milk, 40.5% (15/37) from hand swabs, 60.5% (158/261) from slurry samples. Moreover, of the <i>E. coli</i> isolates, 11.51% (16/139) from milk, 24.32% (09/37) from hand swabs and 31.42% (82/261) from slurry samples were resistant to 5 or more antimicrobial classes. On molecular characterisation, 19.4% (27/139) of <i>E. coli</i> isolates from milk, 37.8% (14/37) from hand swabs, and 33.3% (87/261) from slurry samples harboured various genes. Principal component analysis and Shannon-Wiener diversity indices highlighted varying <i>β</i>-lactamase (ESBL/AmpC β-lactamase) gene distributions across samples, with milk exhibiting the highest diversity. Logistic regression analysis revealed a significant protective effect of milk hygiene scores against <i>E. coli</i> occurrence (OR = 0.18; 95% CI: 0.13-0.26, <i>p</i> < 0.001), while linear regression demonstrated a significant negative association between milk hygiene scores and the Multiple Antibiotic Resistance (MAR) index (<i>p</i> = 0.02). Biofilm assays revealed that 19.2% of isolates were strong biofilm formers, with a strong association (<i>p</i> < 0.01) between biofilm formation potential and MAR index. The multidrug-resistant (MDR) isolates were predominantly moderate biofilm producers, with 23.5% (milk), 20% (hand swabs), and 24.1% (slurry) classified as strong biofilm formers. The study findings underscore the need for One Health-integrated strategies to holistically address AMR challenges at the dairy-environment interface.