Table_1_Comparative microbiome analysis of beef cattle, the feedyard environment, and airborne particulate matter as a function of probiotic and antibiotic use, and change in pen environment.XLSX

IntroductionIntensive beef cattle production systems are frequently implicated as a source of bacteria that can be transferred to nearby humans and animals via effluent water, manure used as fertilizer, or airborne particulate matter. It is crucial to understand microbial population dynamics due to manure pack desiccation, antibiotic usage, and antibiotic alternatives within beef cattle and their associated feedyard environment. Understanding how bacterial communities change in the presence of antibiotics can also improve management practices for reducing the spread of foodborne bacteria.MethodsIn this study, we aimed to compare the microbiomes within cattle feces, the feedyard environment and artificially produced airborne particulate matter as a function of pen change and treatment with tylosin or probiotics. We utilized 16S rRNA sequencing to compare bacterial communities among sample types, study days, and treatment groups.ResultsBacterial community diversity varied as a function of sampling day and pen change (old or new) within fecal and manure pack samples. Manure pack samples from old pens and new pens contained diverse communities of bacteria on days 0 and 84; however, by day 119 of the study these taxonomic differences were less evident. Particulate matter samples exhibited significant differences in community diversity and predominant bacterial taxa compared to the manure pack they originated from. Treatment with tylosin did not meaningfully impact bacterial communities among fecal, environmental, or particulate matter samples; however, minor differences in bacterial community structure were observed in feces from cattle treated with probiotics.DiscussionThis study was the first to characterize and compare microbial communities within feces, manure pack, and airborne particulate matter from the same location and as a function of tylosin and probiotic treatment, and pen change. Although fecal and environmental samples are commonly used in research studies and other monitoring programs to infer public health risk of bacteria and antimicrobial resistance determinants from feedyard environments, our study suggests that these samples may not be appropriate to infer public health risk associated with airborne particulate matter.</p

Effects of Menthol Supplementation in Feedlot Cattle Diets on the Fecal Prevalence of Antimicrobial-Resistant <i>Escherichia coli</i>

<div><p>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 <i>in vitro</i> 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 <i>tet</i> genes in <i>E</i>. <i>coli</i> isolates. Results revealed no effect of menthol supplementation on total coliforms counts or prevalence of <i>E</i>. <i>coli</i> 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 <i>E</i>. <i>coli</i> (<i>P</i> < 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.</p></div

Prevalence of <i>tet</i>A or <i>tet</i>B in fecal <i>Escherichia coli</i> phenotypically resistant to tetracycline in steers fed diets supplemented with or without 0.3% menthol.

<p>Prevalence of <i>tet</i>A or <i>tet</i>B in fecal <i>Escherichia coli</i> phenotypically resistant to tetracycline in steers fed diets supplemented with or without 0.3% menthol.</p

Multidrug resistance (MDR; ≥ 5 antimicrobials) prevalence (%) in fecal <i>Escherichia coli</i> from steers fed diets supplemented with or without 0.3% menthol.

<p>Multidrug resistance (MDR; ≥ 5 antimicrobials) prevalence (%) in fecal <i>Escherichia coli</i> from steers fed diets supplemented with or without 0.3% menthol.</p

Prevalence of tetracycline resistant isolates that do not carry <i>tet</i>A or <i>tet</i>B genes in fecal <i>Escherichia coli</i> in steers fed diets supplemented with or without 0.3% menthol.

<p>Prevalence of tetracycline resistant isolates that do not carry <i>tet</i>A or <i>tet</i>B genes in fecal <i>Escherichia coli</i> in steers fed diets supplemented with or without 0.3% menthol.</p

Prevalence of antimicrobial-resistant fecal <i>Escherichia coli</i> isolates from cattle fed diets with or without 0.3% menthol.

<p>Prevalence of antimicrobial-resistant fecal <i>Escherichia coli</i> isolates from cattle fed diets with or without 0.3% menthol.</p