Abstract
The pool of antimicrobial resistance determinants in the environment and in the gut flora of cattle is a serious public health concern. In addition to being a source of human exposure, these bacteria can transfer antibiotic resistance determinants to pathogenic bacteria and endanger the future of antimicrobial therapy. The occurrence of antimicrobial resistance genes on mobile genetic elements, such as plasmids, facilitates spread of resistance. Recent work has shown in vitro anti-plasmid activity of menthol, a plant-based compound with the potential to be used as a feed additive to beneficially alter ruminal fermentation. The present study aimed to determine if menthol supplementation in diets of feedlot cattle decreases the prevalence of multidrug-resistant bacteria in feces. Menthol was included in diets of steers at 0.3% of diet dry matter. Fecal samples were collected weekly for 4 weeks and analyzed for total coliforms counts, antimicrobial susceptibilities, and the prevalence of tet genes in E. coli isolates. Results revealed no effect of menthol supplementation on total coliforms counts or prevalence of E. coli resistant to amoxicillin, ampicillin, azithromycin, cefoxitin, ceftiofur, ceftriaxone, chloramphenicol, ciprofloxacin, gentamicin, kanamycin, nalidixic acid, streptomycin, sulfisoxazole, and sulfamethoxazole; however, 30 days of menthol addition to steer diets increased the prevalence of tetracycline-resistant E. coli (P < 0.02). Although the mechanism by which menthol exerts its effects remains unclear, results of our study suggest that menthol may have an impact on antimicrobial resistance in gut bacteria.
Highlights
The rise of antimicrobial-resistant bacteria has been observed worldwide [1] and is a growing concern because of its potential to endanger the future of antimicrobial drug therapy [2]
The multidrug resistance plasmid IncA/C found in enteric bacteria, such as Salmonella enterica and Escherichia coli, often encodes for resistance to common antimicrobial agents such as tetracycline, chloramphenicol/florfenicol, streptomycin/spectinomycin, sulfonamides, and extended spectrum β-lactamases, and its spread to pathogenic bacteria may limit antibacterial means to fight infections caused by these bacteria
Based on the known antimicrobial activity of menthol against E. coli, we hypothesized that menthol would impact total coliform counts in cattle fecal samples
Summary
The rise of antimicrobial-resistant bacteria has been observed worldwide [1] and is a growing concern because of its potential to endanger the future of antimicrobial drug therapy [2]. Menthol and Antimicrobial Resistance in E. coli ruminants’ gut flora, represents a large reservoir of antibiotic-resistant bacteria and resistance gene determinants, which can spread to the environment and to humans [5, 6]. The genes encoding for AMR, including multidrug resistance (MDR), are often carried on mobile genetic elements such as plasmids, transposons, and integrons [7, 8, 9], which facilitate horizontal transfer [10] from commensal to pathogenic bacteria and from livestock to human bacterial flora. Compounds capable of limiting or preventing emergence of AMR and/or eliminating or inactivating mobile genetic elements may be of use in controlling antibiotic resistance dissemination, as well as MDR bacteria, and preserving antimicrobial efficacy
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