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

Aims: 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.
Methods and Results: 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 on chromosome 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.
Conclusions: The study illustrated diverse MLSB phenotypes, multiple
resistance genes and transferable plasmids among enterococci isolated from
naturally fermented foods.
Significance and Impact of the Study: 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.