Submitted to: Avian Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/30/2005
Publication Date: 3/1/2006
Citation: Jackson, C.R., Debnam, A.L., Barrett, J.B., Hofacre, C.L. 2006. Effect of subtherapeutic antimicrobials on genetic diversity of enterococcus faecium from chickens. Avian Diseases. 50(1):115-119. Interpretive Summary: Although the effect of growth promoting antimicrobials on antimicrobial susceptibility of Enterococcus faecium from poultry has been previously reported, information is lacking on what effect the antimicrobials have on the genetic diversity of this species. Enterococcus faecium is one of the most studied species of enterococci due to its ability to acquire multiple antimicrobial resistance genes and to cause disease in the immunocompromised human host. In this study, the effect of three growth promoting antimicrobials (bacitracin, flavomycin, and virginiamycin) on the genetic population of Enterococcus faecium from chick boxliners, litter, feed, and carcasses was determined. Results from the study indicated that genetic diversity of Enterococcus faecium was not altered by antimicrobial use and that poultry Enterococcus faecium are a very heterogeneous population. These data will assist researchers who study the effects of growth promotants on bacterial populations in poultry and will enable policy makers to make science based decisions regarding continued use of antimicrobials for growth promotion.
Technical Abstract: The effect of growth promotants (bacitracin, virginiamycin, and flavomycin) on the genetic population of Enterococcus faecium isolated from a commercially integrated poultry farm was examined. A total of 551 Enterococcus faecium were isolated from chick boxliners (n=16), litter (n=334), feed (n=67), and carcass rinse (n=134) samples from four poultry houses. Two houses on the farm were control houses and did not use any antimicrobials while two other houses on the farm used flavomycin, virginiamycin, and bacitracin during six different poultry grow-outs. BOX-PCR and Pulsed-Field Gel Electrophoresis (PFGE) results indicated that Enterococcus faecium strains had a high degree of genetic diversity as overall clustering was independent of source, house, or grow-out. Similarity was greater than 60% for the majority of BOX-PCR genogroups and was greater than 80% for the majority of PFGE genogroups observed for a subset of carcass rinse samples (n=45). Seventy-nine percent (19/24) of isolates in BOX-PCR genogroup 2 also clustered in PFGE genogroup 2 although no association between the isolates and house or grow-out was observed. These results suggest that Enterococcus faecium from poultry are genetically diverse, and that growth-promoting antimicrobials do not affect the genetic population of Enterococcus faecium.