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

Assessment of Antimicrobial Exposure on Generic Escherichia coli and Enterococcus spp. Concentration, Prevalence, and Resistance to Antimicrobials in Beef Cattle Raised with or Without Antimicrobials

The aim was to longitudinally evaluate the association between antimicrobial exposure and resistance occurrence within generic Escherichia coli and Enterococcus spp. populations in feedlot beef cattle raised conventionally or raised without antimicrobials. Angus steers (n = 180) were sorted into 1 of 2 treatments over 2 consecutive years (108 in yr 1 and 72 in yr 2): steers raised without antimicrobials (NAT) and conventionally raised steers exposed to antimicrobials (CONV). Pens within treatment were adjacent and separated by five empty pens from the other treatment. Monensin and tylosin were included in CONV steer diets. On d 123, CONV steers received a metaphylactic antimicrobial. Longitudinal diet (n = 6/year) and fecal (n = 5/year) sampling timepoints were collected to determine E. coli and Enterococcus spp. concentration, prevalence, and resistance patterns. Dietary Enterococcus spp. concentrations, and erythromycin (8ERYR; 128ERYR), tetracycline (TETR), trimethoprim-sulfamethoxazole (COTR), and cefotaxime (CTXR) resistant E. coli concentrations and prevalence were greater in NAT diets than CONV diets (p < 0.02). Fecal E. coli concentrations tended to be greater in NAT steers than CON steers (p = 0.07). Fecal TETR E. coli concentrations were greater in CONV steers than NAT steers (p = 0.03). Fecal COTR and CTXR E. coli prevalence was greater for CONV steers at the beginning of the finishing phase while greater for NAT steers at the end of the finishing phase (p < 0.01). Fecal Enterococcus spp. concentrations did not differ between treatments (p = 0.11). Concentrations of 8ERYR and 128ERYR Enterococcus spp. were greater in CONV steers on d 64, 130, and 168 than NAT steers (p < 0.05). Overall, antimicrobial resistant Enterococcus spp. and E. coli were detected regardless of antimicrobial exposure.

Potential of the livestock industry environment as a reservoir for spreading antimicrobial resistance

Antimicrobial resistance (AMR) in bacteria is a global issue requiring serious attention and management. The indiscriminate use of antibiotics in livestock for growth promotion, disease prevention, and treatment has led to the dissemination of AMR bacteria and resistance genes into the environment. In addition, unethical antibiotic sales without prescriptions, poor sanitation, and improper disposal cause significant amounts of antibiotics used in livestock to enter the environment, causing the emergence of resistant bacteria. Intensive livestock farming is an important source of AMR genes, environmental bacteria contamination, and possible transfer to human pathogens. Bacteria intrinsically antibiotic resistant, which are independent of antibiotic use, further complicate AMR and increase the risk of morbidity and mortality following infections by AMR bacteria. Escherichia coli, Salmonella spp., and Staphylococcus spp. are commonly found in livestock that carry resistance genes and have a risk of human infection. The impact of AMR, if left unchecked, could lead to substantial public health burdens globally, with a predicted mortality rate higher than cancer by 2050. "One Health" integrates strategies across human, animal, and environmental health domains, including improving antibiotic stewardship in livestock, preventing infection, and raising awareness regarding the judicious use of antibiotics. The use of antibiotic alternatives, such as prebiotics, probiotics, bacteriophages, bacteriocins, and vaccinations, to control or prevent infections in livestock will help to avoid over-reliance on antibiotics. Coordinated international actions are needed to mitigate the spread of AMR through improved regulations, technology improvements, and awareness campaigns.

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].

Effects of age and pasture type on the concentration and prevalence of tetracycline and macrolide resistant Enterococcus species in beef cow-calf production system

Enterococci are a normal flora of the gastrointestinal tracts of humans and animals. Enterococci can also cause life-threatening nosocomial infections. Antimicrobial-resistant Enterococcus species have been reported in the feedlot and dairy cattle productions and in meat and milk products, suggesting their foodborne importance. Cow-calf operations represent a significant segment in the beef production system by producing weaned calves. Weaned calves are brought into the feedlot to be finished for meat, and culled cows are also slaughtered for beef, primarily for ground beef products. Infection dynamics in the cow-calf operation can contribute to meat contamination. This study evaluated the effects of age and wheat grazing on the concentration and prevalence of a macrolide antibiotic erythromycin (ERYr) and tetracycline (TETr) resistant enterococci, associated resistance genes and species distribution in a cow-calf production system. In 2017 and 2018, 32 Angus breed cow-calf pairs were randomly assigned to feed on tall fescue or wheat pasture in two independent field experiments. During the grazing experiments of 2-3 weeks, fecal samples were collected weekly and cultured to enumerate, isolate and identify ERYr, TETr, and generic enterococci, using media supplemented with erythromycin, tetracycline or non-supplemented media, respectively. The two main species frequently associated with human illnesses, Enterococcus faecium and E. faecalis, were widely distributed in the cow-calf groups. Generic and TETr- enterococci were prevalent (96-100% prevalence) and abundant (3.2-4.9 log10 CFU/g) in the cow-calf population; however, ERYr enterococci were enumerable by direct plating only from a single cow despite being detected in at least 40% of the fecal samples after enrichment, showing their low abundance. TET- and ERY-resistance were mainly conferred by tet(M) and erm(B), respectively. Wheat grazing reduced the concentration of TETr enterococci and modified enterococcal species and resistance gene distributions. Hence, it is necessary to further investigate wheat grazing in cow-calf production as a potential strategy to mitigate antimicrobial resistance.