Presence and mechanism of antimicrobial resistance among enterococci from cats and dogs

The presence and mechanism of acquired resistance to erythromycin, tylosin, lincomycin, quinupristin/dalfopristin, tetracycline, chloramphenicol, gentamicin, kanamycin, and vancomycin were determined in 97 and 104 enterococci isolated from rectal swabs of cats and dogs, respectively. Eleven feline and three canine enterococcal isolates contained the aac(6')-Ie-aph(2)-Ia gene encoding high-level resistance to gentamicin, an antibiotic often used for treating enterococcal infections in humans. The combination of erm(B) and vat(E) genes encoding resistance to streptogramins was detected in one canine quinupristin/dalfopristin-resistant Enterococcus faecium isolate. Four quinupristin/dalfopristin-resistant enterococci only contained the erm(B) gene. Cross resistance against macrolides and lincosamides (30%) and resistance against tetracyclines (55%) was found to be widely distributed among enterococci from pets. In all of the feline and in 93% of the canine macrolide and lincosamide-resistant isolates, this resistance was encoded by the erm(B) gene. tet(M) was the most prevalent tetracycline resistance gene. It was detected in 91% of the feline and 86% of the canine tetracycline-resistant enterococci. A high occurrence of the Tn916/Tn1545 transposon family was found among these tet(M)-positive isolates. Enterococci from pet animals with resistance against vancomycin were not found. This study shows that enterococci from the intestinal microbiota of cats and dogs may act as a reservoir of resistance genes for animal or human pathogens.