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

INTRODUCTION

The extended-spectrum beta-lactamase (ESBL)-producing such as , 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- in the United States dairy farms. This study aimed to determine the prevalence and AMR pattern of ESBL- in East Tennessee dairy cattle farms.

METHODS

Rectal fecal samples from dairy cattle ( = 508) and manure ( = 30), water ( = 19), and feed samples ( = 15) were collected from 14 farms. The presumptive 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- isolates.

RESULTS AND DISCUSSION

From 572 fecal and farm environmental samples, a total of 233 (41%,  = 572) ESBL- were identified. The prevalence of fecal ESBL- was 47.5% (95% CI: 46.2-49.2). The within-farm prevalence of ESBL- ranged from 8 to 100%. Recent treatment history with third-generation cephalosporins (3GC), cow parity ≥3, and calves were the independent risk factors associated ( < 0.05) with fecal carriage of ESBL-. Overall, 99.6% ( = 231) ESBL- 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%;  = 231 isolates), and ceftriaxone (98.7%,  = 231). Most ESBL- 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- 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- suggests that dairy cattle can be a reservoir for these bacteria, highlighting the associated public health risk.