Effects of Tylosin, a Direct-Fed Microbial and Feedlot Pen Environment on Phenotypic Resistance among Enterococci Isolated from Beef Cattle Feces

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

Introduction

Intensive 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.

Methods

In 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.

Results

Bacterial 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.

Discussion

This 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.

Effect of continuous in-feed administration of tylosin to feedlot cattle on macrolide and tetracycline resistant enterococci in a randomized field trial

Liver abscess causes substantial economic loss to the beef cattle industry through liver condemnation, reduced animal performance, and carcass yield. Continuous in-feed use of tylosin is the most effective and a commonly used practice in beef cattle production to prevent liver abscess. However, such mass medication can increase the level of antimicrobial resistant bacteria. We investigated the effect of continuous in-feed use of tylosin in feedlot cattle on (i) concentrations and prevalence of erythromycin-resistant (ERY^r) and tetracycline-resistant (TET^r) enterococci; (ii) associated antimicrobial resistance genes (ARGs) for resistance; (iii) species distribution; iv) macrolide and tetracycline resistance gene concentrations; and (v) tylosin concentration. A cohort of weaned calves were randomized to receive tylosin-medicated feed (Tylosin; n = 10) or nonmedicated feed (Control; n = 10) for a full feedlot cycle. Feces, feed and pen-surface samples were collected and processed by culture, droplet digital PCR, and liquid chromatography/mass spectroscopy for bacterial enumeration, detection and characterization, ARG quantification, and tylosin concentration, respectively. Data were analyzed by mixed effects linear- or binary-regression models depending on the outcomes. Tylosin administration significantly increased fecal concentration (P < 0.001) and prevalence (P = 0.021) of ERY^r enterococci and erm(B) gene concentration (P < 0.001), compared to the control group. Interestingly, tylosin administration significantly reduced (P = 0.037) fecal TET^r enterococci concentration compared to the control group, with no significant effect (P = 0.758) on fecal tet(M) concentration. In both treatment groups, enterococci concentrations increased over time, peaking on 174 days in feed before returning to the baseline. ERY^r enterococci concentration was significantly (P = 0.012) higher in tylosin medicated feeds, with no significant effect (P = 0.321) on TET^r enterococci concentration. Pen-surface concentration of ermB was significantly (P = 0.024) higher in the tylosin group, with no significant effect (P > 0.05) on bacterial concentrations. Increased diversity and a shift in the composition of enterococcal species and ARGs were observed over time, although tylosin use did not significantly affect (P > 0.05) their prevalence. Tylosin concentration was significantly higher in the feces of tylosin administered cattle (P < 0.001) and medicated feed (P = 0.027), with numerically higher pen-surface concentration (P = 0.065) in the tylosin group. In conclusion, continuous in-feed use of tylosin in feedlot cattle increases macrolide resistant enterococci and its fecal excretion, while decreasing tetracycline resistance. Two medically important species, E. faecium and E. faecalis, were predominant regardless of resistance status or sample source. Risk-based approaches including label changes to limit tylosin use such as withdrawal period, and development of effective manure treatments are potential areas of research to reduce environmental and public health impacts.

Factors associated with antimicrobial resistant enterococci in Canadian beef cattle: A scoping review

Introduction

Antimicrobial resistance (AMR) is a global health concern, occurring when bacteria evolve to render antimicrobials no longer effective. Antimicrobials have important roles in beef production; however, the potential to introduce AMR to people through beef products is a concern. This scoping review identifies factors associated with changes in the prevalence of antimicrobial-resistant Enterococcus spp. applicable to the Canadian farm-to-fork beef continuum.

Methods

Five databases (MEDLINE, BIOSIS, Web of Science, Embase, and CAB Abstracts) were searched for articles published from January 1984 to March 2022, using a priori inclusion criteria. Peer-reviewed articles were included if they met all the following criteria: written in English, applicable to the Canadian beef production context, primary research, in vivo research, describing an intervention or exposure, and specific to Enterococcus spp.

Results

Out of 804 screened articles, 26 were selected for inclusion. The included articles discussed 37 factors potentially associated with AMR in enterococci, with multiple articles discussing at least two of the same factors. Factors discussed included antimicrobial administration (n = 16), raised without antimicrobials (n = 6), metal supplementation (n = 4), probiotics supplementation (n = 3), pen environment (n = 2), essential oil supplementation (n = 1), grass feeding (n = 1), therapeutic versus subtherapeutic antimicrobial use (n = 1), feeding wet distiller grains with solubles (n = 1), nutritional supplementation (n = 1) and processing plant type (n = 1). Results were included irrespective of their quality of evidence.

Discussion

Comparability issues arising throughout the review process were related to data aggregation, hierarchical structures, study design, and inconsistent data reporting. Findings from articles were often temporally specific in that resistance was associated with AMR outcomes at sampling times closer to exposure compared to studies that sampled at longer intervals after exposure. Resistance was often nuanced to unique gene and phenotypic resistance patterns that varied with species of enterococci. Intrinsic resistance and interpretation of minimum inhibitory concentration varied greatly among enterococcal species, highlighting the importance of caution when comparing articles and generalizing findings.

Systematic Review Registration

[http://hdl.handle.net/1880/113592].