SmaI Typeability and Tetracycline Susceptibility and Resistance in Streptococcus pyogenes Isolates with Efflux-Mediated Erythromycin Resistance

These findings contribute to conclusively clarifying why, S. pyogenes isolates with the M phenotype, the tetracycline- ones are, as a rule, SmaI typeable, while the -susceptible ones are not. Previous studies have that, while the two related genetic elements (Tn1207.3 10394.4) typical of tetracycline-susceptible isolates are into the same prophage, the tet(O)-mef(A) element of tetracycline-resistant isolates is inserted into a different (6). The present results show that the R-M encoding, in Tn1207.3-10394.4, the methyltransferase for DNA resistance to cleavage by SmaI is in the tet(O)-mef(A) element where, together with an ORF, it is replaced by three new ORFs flanked, both and downstream, by homologous regions.