Transfer of tetracycline resistance genes with aggregation substance in food-borne Enterococcus faecalis.

Enterococcus faecalis has the ability to conjugate with the aid of aggregation substance (AS) and inducible sex pheromones to exchange genetic elements in food matrix. To evaluate the food safety condition and the transferable factor, 250 tetracycline-resistant food-borne E. faecalis were collected in Korea. Among the isolates, a majority of tetracycline-resistant isolates (49.6 %) harbored both the tet(M) and tet(L) genes together, followed by tet(M) (19.6 %), and tet(L) (6.8 %) alone. Also, we found the combination of tet(L)/tet(M)/tet(O) or tet(M)/tet(O). We identified two tet(S) genes including the isolate carrying tet(M) + tet(S) genes. Additionally, most E. faecalis were positive for cpd and ccf (both 96.8 %) followed by cob (57.2 %). Through mating experiments, we confirmed E. faecalis possessing the Int-Tn gene and/or any AS gene successfully transferred tet genes to JH2-2 E. faecalis, whereas neither E. faecalis carrying AS genes nor the Int-Tn gene showed the conjugation. Pulsed-field gel electrophoresis results supported a distinct pattern, implying transfer of genetic information. Our study revealed a high occurrence of tetracycline resistance genes in E. faecalis from various foods. The widespread dissemination of tetracycline resistance genes would be promoted to transfer tetracycline resistance genes by pheromone-mediated conjugation systems.

Molecular characterization of high-level gentamicin-resistant Enterococcus faecalis from chicken meat in Korea.

Because the intrinsically antimicrobial-resistant Enterococcus has acquired high-level aminoglycoside resistance genes, treating enterococcal infections is difficult. In this study, of the 101 food-borne Enterococcus faecalis isolates collected from retail chicken meat between 2003 and 2010, 11 high-level gentamicin-resistant (HLGR) E. faecalis isolates (MICs>2,048 µg/mL) were found. Molecular characterization was performed to determine the basis of this resistance. All HLGR E. faecalis isolates encoded aac(6')-Ie-aph(2″)-Ia and harbored at least 3 virulence traits in the asa1, esp, gelE, efaA, ace, and cylA genes. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were performed to characterize their molecular epidemiology. A total of 8 sequence types (STs), including 3 novel STs, were identified (ST35, ST82, ST116, ST202, ST300, ST403, ST407, and ST420). ST82, which is associated with amyloid arthropathy in poultry, was the most prevalent ST among HLGR E. faecalis isolates (4 out of 11 isolates, 36.4%); all other STs were identified in the isolates as well. The STs of food-borne HLGR E. faecalis in this study have been confirmed as corresponding to clinical isolates in the MLST database (DB), except for ST300 and the new STs. Three out of 11 isolates belonged to CC116, including ST116, ST407, and ST420. This study characterized HLGR E. faecalis isolates and provided evidence for the spread of HLGR E. faecalis with virulence factors to chicken sources in Korea. The emergence of food-borne HLGR E. faecalis suggests that chicken could be a potential source of transmission of antimicrobial resistance and virulence factors.