Cloned ermTR gene confers low level erythromycin but high level clindamycin resistance in Streptococcus pyogenes NZ131

<p><strong>Objectives:</strong> The most common macrolide resistance mechanisms in <i>streptococci</i> are the presence of methylase encoding genes <i>ermB</i> and <i>ermTR</i> or the presence of efflux encoded by mef genes. In the present study we aimed to show the effects of the <i>ermTR</i> gene under isogenic conditions on the activities of macrolides and lincosamides in <i>streptococci</i>.</p> <p><strong>Materials and Methods: </strong> Total DNA was extracted from <i>Streptococcus pyogenes</i> C1, and the <i>ermTR</i> gene was amplified with or without the regulatory region using modified primer with insertion of restriction sites to clone in to pUC18. Transformants were selected after electroporation of <i>Escherichia coli</i> DB10. The recombinant plasmids were purified and merged to pJIM2246 to transform Gram positive bacteria. Recombinant pJIM2246 plasmids with the <i>ermTR</i> gene were then introduced into <i>S. pyogenes</i> NZ131 by electroporation.</p> <p><strong>Results: </strong> After transformation with <i>ermTR</i> without regulatory region the minimal inhibitory concentration (MIC) for erythromycin and clindamycin increased from ≤0.06 to ≤0.06 to 8 and >128 mg/L, respectively. Induction with erythromycin affected the MICs for clindamycin of <i>S. pyogenes</i> transformed with <i>ermTR</i> with the regulatory region. Double disk testing showed that induction with erythromycin and azithromycin for the <i>S. pyogenes</i> transformed with <i>ermTR</i>, and regulatory regions decreased the clindamycin inhibition zone but not telithromycin. The <i>ermTR</i> gene in isogenic conditions confers low level resistance to erythromycin and high level resistance to clindamycin.</p> <p><strong>Conclusion: </strong> The different induction and resistance profiles of <i>ermTR</i> compared to other <i>erm</i> genes suggest that the methylation of <i>ErmTR</i> may be different than well studied methylases.</p>