Antibiotic resistance in faecal bacteria isolated from horses receiving virginiamycin for the prevention of pasture-associated laminitis

摘要

Enterococcus faecium, a major cause of potentially life-threatening hospital-acquired human infections, can be resistant to several antimicrobials, such that streptogramin quinupristin dalfopristin (QJD) is one of the few antibiotics still effective. Consequently use of the streptogramin virginiamycin as an animal growth promoter was banned in the EU in 1999 as some believed this contributed to the emergence of QJD resistant E. faecium. Virginiamycin is advocated for preventing equine pasture-associated laminitis, but its effect on equine faecal bacterial QJD resistance has not been determined. Faecal samples were obtained from horses receiving virginiamycin, horses co-grazing and horses not exposed to virginiamycin. Streptogramin resistant E. faecium were cultured from 70% (21/30) of animals treated with virginiamycin, 75% (18/24) of co-grazing animals and 69% (11/16) of animals not exposed. ermB and vatD genes were detected using real time PCR in 63% and 66% of animals treated with virginiamycin, 75% and 71% of co-grazing animals and 63% and 69% of animals not exposed. Antimicrobial resistance genes were present only in samples which had cultured QJD resistant E. faecium. There was no significant difference between groups with respect to antimicrobial resistance. The gene load of vatD was significantly (p = 0.04) greater in unexposed animals compared to those treated with virginiamycin. The use of virginiamycin to prevent pasture-associated laminitis does not appear to be related to an increased Q/D resistance frequency. However, in view of the high frequency of resistance within all groups, the horse is a reservoir of QJD resistant genes and clones that potentially could be transferred transiently to humans