Antimicrobial Resistance Among Escherichia coli Isolated from Veal Calf Operations in Pennsylvania

Antimicrobial resistance (AR) is a pressing public health concern, and agricultural operations such as dairy and beef cattle production have been implicated as potential sources of resistant bacteria or genetic elements. This study aimed to determine the prevalence of antimicrobial-resistant Escherichia coli from calf pens in 6 auction houses (56 manure composite samples) and 12 veal calf operations (240 fecal samples in 2 visits: after the calves arrived at the farm and shortly before the animals were sent to slaughter) in the Commonwealth of Pennsylvania. A total of 1567 generic E. coli were isolated and screened for resistance phenotypes. Resistant E. coli were isolated from all auction houses and farms sampled. Based on nonparametric Kruskal-Wallis tests, incremental prevalence of E. coli resistant to ampicillin, azithromycin, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, streptomycin, sulfisoxazole, trimethoprim-sulfamethoxazole, and tetracycline in the samples from auction houses and the first and second farm visits was observed (χ² 6.98-15.91, p < 0.05). Multidrug-resistant E. coli (resistant to more than three antimicrobial classes) were identified in 76.8%, 90.8%, and 100% of samples collected from the auction houses, first farm visits, and second farm visits, respectively. The presence of bla_CTX-M-E. coli in 11 of the 12 farms presents the possibility of veal production environments being a reservoir for resistant genetic materials that may pose a risk to human health if they are transferred to human pathogens. Additional research on the impact of various management strategies in veal calf rearing is needed for a complete scenario of AR in these production environments.