Phenotypic expression, molecular characterization and transferability of erythromycin resistance genes in Enterococcus spp. isolated from naturally fermented food

Abstract

To evaluate phenotypic resistance to macrolides-lincosamides and streptogramin B (MLSB ) antibiotics and to determine their localization as well as transferability of erythromycin resistance genes in enterococcal isolates of naturally fermented food-Idli batter. Diverse MLSB phenotypes observed among the enterococcal spp. (n=32) were analysed through double disc and triple disc test. Standard minimum inhibitory concentration tests along with induction studies displayed synergistic or cross-resistance among MLSB antibiotics. Plasmid profiling and Southern hybridization revealed that erm(B) and msr(C) genes were localized either onchromosome or on high molecular weight plasmids and showed co-localization of these genes with lnu(B), tet(L) and tet(W) in one of the isolate. In vitro conjugation experiments demonstrated plasmid-mediated transfer of erm(B) gene from three Enterococcus durans strains to Enterococcus faecalis JH2-2. The study illustrated diverse MLSB phenotypes, multiple resistance genes and transferable plasmids among enterococci isolated from naturally fermented foods. From a public health point of view, the study identified that naturally fermented foods could represent a source of antibiotic resistance enterococci that can spread through foods. These results also suggest that vigilance may be exercised with the use of combination or novel MLSB antibiotics in treating enterococcal infections.