Prevalence and antimicrobial resistance profiles of extended-spectrum beta-lactamase-producing Escherichia coli in East Tennessee dairy farms.

Introduction: The extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae, such as Escherichia coli , are emerging as a serious threat to global health due to their rapid spread and their multidrug-resistant (MDR) phenotypes. However, limited information is available regarding the prevalence and antimicrobial resistance (AMR) profile of ESBL- E. coli in the United States dairy farms. This study aimed to determine the prevalence and AMR pattern of ESBL- E. coli in East Tennessee dairy cattle farms.
Methods: Rectal fecal samples from dairy cattle ( n  = 508) and manure ( n  = 30), water ( n  = 19), and feed samples ( n  = 15) were collected from 14 farms. The presumptive E. coli was isolated on CHROMagar™ ESBL and confirmed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). Antimicrobial susceptibility testing was performed on the ESBL- E. coli isolates.
Results and Discussion: From 572 fecal and farm environmental samples, a total of 233 (41%, n  = 572) ESBL- E. coli were identified. The prevalence of fecal ESBL- E. coli was 47.5% (95% CI: 46.2-49.2). The within-farm prevalence of ESBL- E. coli ranged from 8 to 100%. Recent treatment history with third-generation cephalosporins (3GC), cow parity ≥3, and calves were the independent risk factors associated ( P  < 0.05) with fecal carriage of ESBL- E. coli . Overall, 99.6% ( n = 231) ESBL- E. coli tested were phenotypically resistant to at least one of the 14 antimicrobial agents tested. The most common AMR phenotypes were against beta-lactam antibiotics, ampicillin (99.1%; n  = 231 isolates), and ceftriaxone (98.7%, n  = 231). Most ESBL- E. coli isolates (94.4%) were MDR (resistance to ≥3 antimicrobial classes), of which 42.6% showed co-resistance to at least six classes of antimicrobials. ESBL- E. coli isolates with concurrent resistance to ceftriaxone, ampicillin, streptomycin, tetracycline, sulfisoxazole, and chloramphenicol are widespread and detected in all the farms. The detection of MDR ESBL- E. coli suggests that dairy cattle can be a reservoir for these bacteria, highlighting the associated public health risk.
Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2023 Gelalcha, Gelgie and Kerro Dego.)