Antimicrobial resistance in Escherichia coli isolates from dairy farms (Santa Fe province, Argentina).

Antimicrobial resistance (AMR) poses a significant global threat, with E. coli serving as an indicator for resistance patterns in pathogens. This study evaluated the prevalence of AMR in E. coli isolates from dairy farms in Santa Fe, Argentina, focusing on two animal categories: pre-weaned calves and lactating cows. A cross-sectional study was conducted from November 2019 to March 2020, yielding 545 E. coli isolates from fecal samples across 54 dairy farms and three collective calf-rearing farms. Resistance was assessed using the disc diffusion test for multiple antimicrobial classes. The study revealed a higher risk of AMR in calf isolates compared to cow isolates, particularly for gentamicin and tetracycline. A significant proportion of isolates were multi-drug resistant (MDR, 25.13%), with MDR isolates predominantly found in calves and collective calf-rearing farms. The MDR isolates were 9 times more probable to be found in calves than in cows (OR = 9.09; P < 0.001). The most frequent antimicrobial (AM) class combination in MDR E. coli isolates were beta-lactams, tetracyclines, and quinolones (75.18%). This study highlights the need for targeted interventions to manage AM use, particularly in young livestock, to mitigate the rise of AMR and its implications for both animal and public health.