Longitudinal characterization of antimicrobial resistance genes in feces shed from cattle fed different subtherapeutic antibiotics
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Date
2011
Authors
Alexander, Trevor W.
Yanke, L. Jay
Reuter, Tim
Topp, Ed
Read, Ronald R.
Selinger, L. Brent
McAllister, Tim A.
Journal Title
Journal ISSN
Volume Title
Publisher
Biomed Central Ltd
Abstract
Background: Environmental transmission of antimicrobial-resistant bacteria and resistance gene determinants
originating from livestock is affected by their persistence in agricultural-related matrices. This study investigated the
effects of administering subtherapeutic concentrations of antimicrobials to beef cattle on the abundance and
persistence of resistance genes within the microbial community of fecal deposits. Cattle (three pens per treatment,
10 steers per pen) were administered chlortetracycline, chlortetracycline plus sulfamethazine, tylosin, or no
antimicrobials (control). Model fecal deposits (n = 3) were prepared by mixing fresh feces from each pen into a
single composite sample. Real-time PCR was used to measure concentrations of tet, sul and erm resistance genes
in DNA extracted from composites over 175 days of environmental exposure in the field. The microbial
communities were analyzed by quantification and denaturing gradient gel electrophoresis (DGGE) of PCR-amplified
16S-rRNA.
Results: The concentrations of 16S-rRNA in feces were similar across treatments and increased by day 56, declining
thereafter. DGGE profiles of 16S-rRNA differed amongst treatments and with time, illustrating temporal shifts in
microbial communities. All measured resistance gene determinants were quantifiable in feces after 175 days.
Antimicrobial treatment differentially affected the abundance of certain resistance genes but generally not their
persistence. In the first 56 days, concentrations of tet(B), tet(C), sul1, sul2, erm(A) tended to increase, and decline
thereafter, whereas tet(M) and tet(W) gradually declined over 175 days. At day 7, the concentration of erm(X) was
greatest in feces from cattle fed tylosin, compared to all other treatments.
Conclusion: The abundance of genes coding for antimicrobial resistance in bovine feces can be affected by
inclusion of antibiotics in the feed. Resistance genes can persist in feces from cattle beyond 175 days with
concentrations of some genes increasing with time. Management practices that accelerate DNA degradation such
as frequent land application or composting of manure may reduce the extent to which bovine feces serves as a
reservoir of antimicrobial resistance.
Description
Sherpa Romeo green journal. Open access article. Creative Commons Attribution 2.0 Generic License (CC BY 2.0) applies
Keywords
Antimicrobial resistance , Bovine feces , Antibiotics , Beef cattle , Antibiotics in animal nutrition
Citation
Alexander, T.W., Yanke, J. L., Reuter, T., Topp, E., Read, R. R., Selinger, L. B., & McAllister, T. A. (2011). Longitudinal characterization of antimicrobial resistance genes in feces shed from cattle fed different subtherapeutic antibiotics. BMC Microbiology, 11:19. doi:10.1186/1471-2180-11-19