Characterization of antibiotic resistance phenotypes and resistance genes in Enterococcus spp. isolated from cheeses

Strains of Enterococcus spp. isolated from a collection of 123 artisanal and industrial cheese samples were studied for the phenotypic and genotypic assessment of antibiotic resistance. A total of 226 isolates included 119 E. faecium (52.65%), 40 E. durans (17.7%), 37 E. hirae (16.37%), 29 E. faecalis (12.83%) and 1 E. gallinarum (0.44%). Out of 61 tested strains, 15 (24.59%) strains exhibited resistance to one or more tested antibiotics, as determined by the disc diffusion method. The resistance phenotypes were as follows: gentamicin (45.45%), tetracycline (31.82%), erythromycin (9.09%), vancomycin (9.09%) and penicillin (4.55%). The presence of tetracycline and erythromycin resistance genes [tet(M), tet(L) and erm(B), respectively] and integrase gene (int), associated with Tn916-1545 transposon family, was detected by PCR procedures. The tet(M) gene was determined in all 7 tested strains, but none of the analyzed strains harbored tet(L) determinant. The erm(B) gene was not detected in 9 strains characterized by phenotypic resistance to erythromycin. All 16 strains were positive for the presence of the int gene. The presented results show the presence of antibiotic resistance genes and the transposon integrase gene associated with transferable resistance in enterococci, indicating a potential for gene transfer through the food chain.