Molecular basis and transferability of tetracycline resistance in Enterococcus italicus LMG 22195 from fermented milk

A tetracycline-resistant Enterococcus italicus strain from fermented milk, LMG 22195, was found to contain a tet(S) gene located on a plasmid of approximately 20 kb. Filter mating demonstrated that the tet(S) gene was transferable from LMG 22195 to the recipient Enterococcus faecalis JH2-2. PCR-based detection and Southern blot experiments revealed that the confirmed transconjugants acquired the tet(S)-carrying plasmid. Similar to the donor strain, transconjugants displayed a tetracycline MIC of 64 μg/ml. Results of this study suggest that E. italicus, like other enterococcal species, is able to disseminate antibiotic-resistance genes, although a more definitive proof on this statement will be provided when a higher number of strains will be tested. Because of the recent isolation of E. italicus from human clinical specimens and its concomitant presence in various dairy products, the ability of this organism to horizontally transfer tet(S) or other resistance genes may potentially pose safety concerns, especially for its possible use in food fermentations.