Effects of in-feed copper and tylosin supplementations on copper and antimicrobial resistance in faecal enterococci of feedlot cattle.
OBJECTIVE
The objective was to investigate whether in-feed supplementation of copper, at elevated level, co-selects for macrolide resistance in faecal enterococci.


RESULTS
The study was conducted in cattle (n = 80) with a 2 × 2 factorial design of copper (10 or 100 mg kg(-1) of feed) and tylosin (0 or 10 mg kg(-1) of feed). Thirty-seven isolates (4·6%; 37/800) of faecal enterococci were positive for the tcrB and all were Enterococcus faecium. The prevalence was higher among cattle fed diets with copper and tylosin (8·5%) compared to control (2·0%), copper (4·5%) and tylosin (3·5%) alone. All tcrB-positive isolates were positive for erm(B) and tet(M) genes. Median copper minimum inhibitory concentrations (MICs) for tcrB-positive and tcrB-negative enterococci were 20 and 4 mmol l(-1) , respectively.


CONCLUSIONS
Feeding of elevated dietary copper and tylosin alone or in combination resulted in an increased prevalence of tcrB and erm(B)-mediated copper and tylosin-resistant faecal enterococci in feedlot cattle.


CONCLUSIONS
In-feed supplementation of elevated dietary copper has the potential to co-select for macrolide resistance. Further studies are warranted to investigate the factors involved in maintenance and dissemination of the resistance determinants and their co-selection mechanism in relation to feed-grade antimicrobials' usage in feedlot cattle.
Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, KS, USA.
R G
RG
Amachawadi
Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, KS, USA.|Department of Veterinary Pathobiology, Texas A&M University, College Station, TX, USA.
H M
HM
Scott
Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS, USA.
C
C
Aperce
Department of Veterinary Pathobiology, Texas A&M University, College Station, TX, USA.
J
J
Vinasco
Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS, USA.
J S
JS
Drouillard
Department of Diagnostic Medicine and Pathobiology, Kansas State University, Manhattan, KS, USA.
T G
TG
Nagaraja
D000821:Animal Feed / Q000032:analysis; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002417:Cattle / Q000382:microbiology*; D003300:Copper / Q000378:metabolism* / Q000494:pharmacology; D019587:Dietary Supplements / Q000032:analysis*; D016983:Enterococcus / Q000145:classification / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D005243:Feces / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D015645:Tylosin / Q000378:metabolism* / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D003300:Copper; D015645:Tylosin
acquired copper resistance; cattle; copper; faecal enterococci; macrolide; macrolide resistance; tetracycline; tylosin