# Susceptibility Profile and Multiple Antibiotics Resistance of Escherichia coli, Klebsiella spp., and Enterococci from Small-Scale Cattle Farms in Tennessee

## TL;DR

This study examines antibiotic resistance in bacteria from small cattle farms in Tennessee, finding high resistance levels in manure and soil, and highlights the need for better antimicrobial practices.

## Contribution

The study provides the first detailed characterization of antimicrobial resistance in small-scale cattle farms in Tennessee, focusing on environmental reservoirs and farmer practices.

## Key findings

- Manure and soil had the highest Multiple Antibiotic Resistance Index (MARI) values, indicating they are high-risk reservoirs for resistant bacteria.
- Enterococcus showed consistent resistance to all three tested antibiotics, while E. coli and Klebsiella exhibited varied resistance patterns.
- Over two-thirds of farmers were aware of antimicrobial resistance as a public health issue, and most consulted veterinarians before antibiotic use.

## Abstract

Background/Objectives: Antimicrobial resistance in food–animal environments threatens sustainable production and public health, yet small farms remain poorly characterized as potential reservoirs of antimicrobial resistant bacteria. To address this, we investigated the prevalence and antimicrobial resistance profiles of Escherichia coli, Klebsiella spp., and Enterococcus spp. from small-scale cattle farms in Tennessee, USA. Methods: Over one year, 153 environmental samples (soil, manure, water) were collected from 17 farms. Target bacteria were isolated and confirmed using selective agar, biochemical tests, and PCR, and tested against 12 antibiotics using the Kirby–Bauer disk diffusion test. Multiple Antibiotic Resistance Index (MARI) and multidrug resistance (MDR) profiles were summarized. A complementary farmer survey of 26 farmers captured veterinary access, antibiotic use, manure handling, record keeping, and awareness of antimicrobial resistance. Results: Prevalence was highest for Enterococcus spp. (41.8%), followed by E. coli (23.5%) and Klebsiella spp. (12.4%). Seasonal variation was significant for E. coli and Enterococcus (p < 0.05). Winter manure yielded highest detection of E. coli (55.6%) and Enterococcus (53.8%), whereas Klebsiella peaked in Fall soil (19.1%). Resistance patterns varied across species, with Enterococcus showing consistent resistance to all three. E. coli frequently resisted erythromycin, ampicillin, and azithromycin; and Klebsiella commonly resisted erythromycin, ampicillin, and cefotaxime, though some of these reflect intrinsic resistance rather than acquired clinical resistance. MARI values were 0.92 in manure and soil, identifying them as high-risk reservoirs. We identified 29 distinct MDR pattern. Bipartite network visualization highlighted “resistance hubs” around erythromycin, ampicillin, and vancomycin, particularly in Enterococcus. In our study, 76.9% of farmers consulted veterinarians before antibiotic use, 57.7% kept written antibiotic records, and 65.4% were aware of AMR as a public health issue. Small-scale cattle farms are potential reservoirs of multidrug resistant commensal bacteria. Conclusions: These findings provide an evidence-based foundation to guide targeted antimicrobial stewardship and promote sustainable management practices in small-scale food animal farms.