Persistence of erythromycin resistance gene erm(B) in cattle feedlot pens over time

Authors: Mantz, Amy; Miller, Daniel; Spiehs, Mindy; Woodbury, Bryan; Durso, Lisa

Submitted to: Agriculture, Food and Analytical Bacteriology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/3/2013
Publication Date: 12/31/2013
Publication URL: https://handle.nal.usda.gov/10113/58338
Citation: Mantz, A.R., Miller, D.N., Spiehs, M.J., Woodbury, B.L., Durso, L.M. 2013. Persistence of erythromycin resistance gene erm(B) in cattle feedlot pens over time. Agriculture, Food and Analytical Bacteriology. 3(4):312-320.

Interpretive Summary: The use of antibiotics in food animals allows for the growth of antibiotic resistant bacteria in the animal’s gastrointestinal tract (GIT). These bacteria carry genes that code for antibiotic resistance. There is concern that the GIT bacteria can share their resistant genes with the bacteria in the environment, which possibly includes human pathogens. Manure is the main transportation vehicle for antibiotic resistant bacteria to enter the environment and become mixed with different types of non-resistant bacteria on and in the soil surface of a feedlot pen. We were interested in exploring whether antibiotic resistance genes that originate in feedlot cattle GIT remain associated with the fecal material once it leaves the animal. If so, methods that are available to identify where in the pen manure is deposited can be used to identify where in the pen the antibiotic resistance genes are likely to be found. In a feedlot pen, manure has a tendency to collect in certain areas (i.e. near the bottom of the gradient and around the edge). The assumption that more antibiotic resistant bacteria would be found in these areas is logical, but our results show this was not true for the feedlot pens we examined. In this cattle feedlot study, diet (corn-based versus distillers byproducts), location within the cattle feedlot pen (mound versus edge sites), and a 13-month period of animal production had little impact on the prevalence of blaSHV and ermB antibiotic resistance genes in a beef cattle feedlot. Resistance genes did not accumulate or lead to “hot spots” within the feedlot.

Technical Abstract: The prevalence of antibiotic resistance was evaluated in cattle feedlot surface soil samples collected prior to and after a 13-month feedlot trial of two common diets, a 0% wet distillers grains plus solubles (WDGS) corn-based ration versus a 35% WDGS ration. Soil samples were collected from the mound and edges of 10 feedlot pens. Following DNA extraction, the samples were screened for two antibiotic resistance genes using PCR analysis. The screen for blaSHV gene resulted in no positives, while the ermB gene was found in 78.3% of samples (n = 240). No differences (P = 0.684) were found between the diet rations. Initial rates of prevalence in June 2009 were different (P= 0.016) between the mound and edge locations, but by the end of the feeding trial in August 2010, no differences were detected (P = 0.584). A comparison of ermB positive and ermB negative soil constituents for the mound and edge on the separate sampling dates found that ermB positive samples generally were more manure-like and had a combination of higher volatile solids, N, P, K, S, and apparent electrical conductance. For blaSHV and ermB, beef cattle production had little impact on their prevalence. Significance and Impact of the Study: Antibiotic resistance has become an important issue for public safety in recent years due to increasing antibiotic resistance in food animals and the potential for horizontal gene transfer occurring in the environment. In this cattle feedlot study, diet (corn-based versus distillers byproducts), location within the cattle feedlot pen (mound versus edge sites), and a 13-month period of animal production had little impact on the prevalence of blaSHV and ermB antibiotic resistance genes in a beef cattle feedlot. Resistance genes did not accumulate or lead to “hot spots” within the feedlot.