A tet(S/M) hybrid from CTn6000 and CTn916 recombination

We read with interest the article by Barile et al. (2012) which describes the first mosaic tet(S/M) gene encoding tetracycline resistance from foodborne strains of Streptococcus bovis. The mosaic tet genes described to date are hybrids of other ribosome protection type [tet(O), tet(32), tet(W)] which are particularly abundant among Firmicutes (Lactobacillus, Bifidobacterium, Streptococcus, Clostridium) isolated from animals (Stanton et al., 2005; Patterson et al., 2007; van Hoek et al., 2008; Palmieri et al., 2012). The origin and nomenclature of such genetically divergent mosaic tet genes remains controversial due to the lack of information about their genetic contexts and the identical size of the resulting proteins (Zheng et al., 2004, Stanton et al., 2005; Palmieri et al., 2012).