A New Integrative and Mobilizable Element Is a Major Contributor to Tetracycline Resistance in Streptococcus dysgalactiae subsp. equisimilis

Tetracycline resistance in streptococci is mainly due to ribosomal protection mediated by the (M) gene that is usually located in the integrative and conjugative elements (ICEs) of the Tn -family. In this study, we analyzed the genes involved in tetracycline resistance and the associated mobile genetic elements (MGEs) in subsp. (SDSE) causing invasive disease. SDSE resistant to tetracycline collected from 2012 to 2019 in a single hospital and from 2018 in three other hospitals were analyzed by whole genome sequencing. Out of a total of 84 SDSE isolates, 24 (28.5%) were resistant to tetracycline due to the presence of (M) ( = 22), (W) ( = 1), or (L) plus (W) ( = 1). The (M) genes were found in the ICEs of the Tn -family ( = 10) and in a new integrative and mobilizable element (IME; = 12). Phylogenetic analysis showed a higher genetic diversity among the strains carrying Tn than those having the new IME, which were closely related, and all belonged to CC15. In conclusion, tetracycline resistance in SDSE is mostly due to the (M) gene associated with ICEs belonging to the Tn -family and a new IME. This new IME is a major cause of tetracycline resistance in invasive subsp. in our settings.