Antibimicrobial susceptibility of trimethoprim sulfamethoxazole and 3rd generation cephalosporin resistant Escherichia coli isolates enumerated longitudinally...

Authors: LONG, NATHAN - Texas Tech University; HALES, KRISTIN - Texas Tech University; BERRY, ELAINE - Former ARS Employee; LEGAKO, JERRAD - Texas Tech University; WOERNER, DALE - Texas Tech University; Broadway, Paul; Carroll, Jeffery - Jeff Carroll; Sanchez, Nicole; FERNANDO, SAMODHA - University Of Nebraska; Wells, James - Jim

Submitted to: Foodborne Pathogens and Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Feedlot cattle that are of a high-risk to develop bovine respiratory disease (BRD) typically receive substantial antibiotic treatments when sick. To reduce the need to treat sick animals later, they often receive antimicrobials upon arrival to the feedlot. Therefore, BRD high-risk cattle are exposed to a variety of antimicrobials within the first month at the feedlot but little is known about antimicrobial resistant (AMR) Escherichia coli in these cattle. Fecal samples were collected over eight months from BRD high-risk cattle that were or were not treated with an antimicrobial at arrival to the feedlot and monitored for AMR in E. coli bacteria. Antimicrobial use at arrival resulted in increased AMR in the E coli populations for up to two months after arrival, but the AMR in E. coli at arrival and harvest were similar.

Technical Abstract: Multi-drug resistant Escherichia coli threaten the preservation of antimicrobials in human medicine and contributions from livestock are unclear. Thus, our objective was to measure if metaphylactic antimicrobials given to high-risk feedlot cattle at arrival causes multi-drug resistant E. coli. Crossbred cattle (n = 249; BW = 244 kg ± 25 kg SD) were blocked by arrival date and assigned metaphylactic antimicrobial treatments of sterile saline control (CON); tulathromycin (TUL); ceftiofur (CEF); or florfenicol (FLR) at random. Trimethoprim sulfamethoxazole (COTR) and 3rd generation cephalosporin (CTXR) resistant E. coli were isolated from fecal samples on d 0, 28, 56, 112, 182, and study END (day 252 for block 1 and day 242 for block 2). Then, susceptibility testing was conducted on all confirmed isolates. Multi-drug resistance was detected in both COTR and CTXR E. coli isolates. In COTR isolates, the number of antimicrobials each isolate was resistant to and the MIC for amoxicillin-clavulanic acid, ceftriaxone, and gentamicin was greatest on d 28 compared to all other days (P = 0.04). Similarly, chloramphenicol MIC was greater on d 28 than d 0 (P < 0.01). Overall, sulfisoxazole MIC was less for TUL than all other treatments (P = 0.02), and trimethoprim sulfamethoxazole MIC was greater for TUL than all other treatments (P = 0.03). Lastly, there was no effect of treatment, day, or treatment × day for tetracycline or meropenem MIC (P = 0.07). In CTXR isolates, there was an effect of day for all antimicrobials tested except ampicillin and meropenem (P = 0.06). In conclusion, administering a metaphylactic antimicrobial at feedlot arrival did influence the susceptibility of COTR and CTXR E. coli. However, multi-drug resistant E. coli are widely distributed, and the MIC for most antimicrobials was not different from the initial value upon completion of the feeding period.