Étude de la résistance aux antibiotiques des entérocoques d'origine animale du Québec

Enterococci are part of normal intestinal gut flora of animals and humans. Many studies have shown that enterococci from animal origin could represent an antimicrobial resistance genes reservoir for the human community. The two species Enterococcus faecalis and Enterococcus faecium are important in public health; they are responsible for approximately 12% of all nosocomial infections in the United States. In Canada, cases of colonization and/or infections to vancomycin resistant enterococci have more than tripled from 2005 to 2009. A total of 387 poultry E. faecalis and E. faecium isolates, and 124 porcine E. faecalis isolates were identified and analyzed for their antibiotic susceptibilities. High percentages of resistance to macrolides and tetracyclines were found in both avian and porcine isolates. Two predominant phenotypic profiles were determined and analyzed by PCR and sequencing for the presence of antimicrobial resistance genes. Various combinations of antibiotic resistance genes were detected; erm(B) and tet(M) were the most common genes. For the first time, plasmid extraction and hybridization revealed colocalization of erm(B) and tet(M) on a plasmid of ~9 kb in porcine E. faecalis isolates, and of erm(B) and tet(O) on a low-molecular-weight plasmid of ~11 kb in poultry E. faecalis isolates. Furthermore, we demonstrated, through mating experiments, these plasmids could be transferred. Results indicate that the intestinal enterococci of healthy pigs and poultry, which can contaminate meat at slaughter, could be a reservoir for quinupristin-dalfopristin, bacitracin, tetracycline, and macrolide resistance genes. To assess the use of a polyclonal antiserum AS on the contact interference of a high level bacitracin resistant (bcrRAB genes) pheromone-responsive plasmid, a multiresistant E. faecalis isolate of poultry origin was selected. After induction with pheromones produced by the recipient strain E. faecalis JH2-2, clumping of the donor E. faecalis strain 543 was demonstrated as well as high transfer frequencies in short time broth mating. Conjugative transfer of asa1, traB and bcrRAB genes and their co-localization were also demonstrated in the donor strain and a transconjugant T543-1 on a plasmid band of 115 kb by PFGE and Southern blotting. A MIC to bacitracin of > 2 048 µg/ml was obtained for both strains 543 and T543-1 whereas the recipient strain JH2-2 demonstrated a MIC of 32 µg/ml. Sequencing of the asa1 gene encoding for an AS, and traB for a pheromone shutdown protein, confirmed the association of this genetic element to the pheromone-responsive plasmid related to pJM01. More significantly, this study presents the evidence that a polyclonal antiserum AS can significantly interfere with the horizontal transfer of a pheromone-responsive plasmid encoding high-level bacitracin resistance of a poultry multidrug resistant E. faecalis strain. Clinical isolates of E. faecium of human and canine origin were analyzed and compared. This report describes for the first time the characterization of canine clinical ampicillin-resistant E. faecium (AREF) isolates related to CC17 (ST17) in Canada. These isolates were resistant to ciprofloxacin and lincomycin. Resistance to ciprofloxacin was confirmed by amino acid substitutions in DNA gyrase (gyrA/gyrB) and topoisomerase IV (parC/parE) genes. High-level gentamicin, -kanamycin and -streptomycin resistances and macrolides resistance were also observed. The frequency of tetracycline resistance was high whereas vancomycin resistance was not detected. Also, no resistance was observed to linezolid and quinupristin-dalfopristin antibiotics. Data demonstrated the complete absence of enterococcal surface protein (esp) and hyaluronidase (hyl) genes among the canine AREF isolates tested while all were acm (collagen adhesin from E. faecium) positive. However, most of them were shown to harbor efaAfm gene, encoding for a cell wall adhesin. No biofilm formation or clustered regularly interspaced short palindromic repeats (CRISPR) elements were identified in these canine AREF isolates. rep6 and rep11 families of plasmids were significantly associated with isolates from dogs. The PFGE patterns of human and dog isolates were considered unrelated (≤ 80%). These findings also support the importance of prudent use of antibiotics in veterinary medicine to avoid zoonotic spread of canine AREF isolates.  We are confident that our results may help to better understand the mechanisms of antibiotic resistance and mobile element carrying them as well as new strategies to reduce the horizontal transfer of antibiotic resistance and virulence traits.

Keyphrases: Enterococcus faecalis, Enterococcus faecium, virulence, commensal, Enterococcus faecalis, Enterococcus faecium, antimicrobial resistance, plasmid, pheromone-responsive conjugation, polyclonal antiserum AS, virulence, commensal, clinical