Species distribution and genes encoding antimicrobial resistance in enterococcus spp. isolates from rabbits residing in diverse ecosystems: A new reservoir of linezolid and vancomycin resistance.

Abstract

Worldwide, studies regarding antimicrobial resistance in rabbits are scarce. In addition, it seems that rearing conditions have important impact on emergence and spread of antimicrobial-resistant bacteria. Thus, the authors sought to (1) assess the role of rabbits residing across diverse ecosystems as potential reservoirs of antimicrobial-resistant enterococci and (2) investigate the genetic background of detected resistances. Faecal samples from 60 healthy farmed rabbits (one farm), 35 laboratory rabbits and 31 wild rabbits were analysed. Overall, 97 enterococci isolates were accumulated, as follows: 44 E. faecium, 37 E. faecalis, 7 E. gallinarum, 5 E. durans and 4 E. avium. E. faecalis isolates were statistically associated with farm rabbits and wild rabbits (p<0.05). High rates of resistance were observed for tetracycline (60.8%; tetM [n=48; 81.3%], tetO [n=7; 11.8%] and tetL [n=1; 1.7%]), erythromycin (43.3%; msr(A) [n=14; 33.3%] and ermB [n=13; 31%]), ampicillin (29.9%), streptomycin (26.8%; ant(6)-Ia [n=3, 11.5%]) and vancomycin (21.6%; vanA [one E. faecium+one E. faecalis; 9.5%]). Low frequencies of resistance were observed for teicoplanin (9.2%), linezolid (8.2%), ciprofloxacin (7.2%) and gentamicin (1%; aac(6')-Ie-aph(2″)-Ia). Resistance to ampicillin and vancomycin was associated with laboratory rabbits (p<0.05). Int-Tn (Tn916/1545) was detected in 27 (27.8%) isolates, of which 10 isolates co-harboured tetM and ermB genes, while 16 comprised tetM. Findings indicate that clinically relevant enterococci species isolated from rabbits are frequently resistant to antimicrobials and harbour a range of genes associated with the Tn916/1545 family. This study highlights the high rates of antimicrobial-resistant enterococci from rabbits and the occurrence of both vancomycin- and linezolid-resistant isolates, potentially representing a very serious threat to human and animal health.