Transcriptional Attenuation Controls Macrolide Inducible Efflux and Resistance in Streptococcus pneumoniae and in Other Gram-Positive Bacteria Containing mef/mel(msr(D)) Elements.

PloS one

PubMedID: 25695510

Chancey ST, Bai X, Kumar N, Drabek EF, Daugherty SC, Colon T, Ott S, Sengamalay N, Sadzewicz L, Tallon LJ, Fraser CM, Tettelin H, Stephens DS. Transcriptional Attenuation Controls Macrolide Inducible Efflux and Resistance in Streptococcus pneumoniae and in Other Gram-Positive Bacteria Containing mef/mel(msr(D)) Elements. PLoS ONE. 2015;10(2):e0116254.
Macrolide resistance, emerging in Streptococcus pneumoniae and other Gram-positive bacteria, is increasingly due to efflux pumps encoded by mef/mel(msr) operons found on discrete mobile genetic elements. The regulation of mef/mel(msr) in these elements is not well understood. We identified the mef(E)/mel transcriptional start, localized the mef(E)/mel promoter, and demonstrated attenuation of transcription as a mechanism of regulation of macrolide-inducible mef-mediated macrolide resistance in S. pneumoniae. The mef(E)/mel transcriptional start site was a guanine 327 bp upstream of mef(E). Consensus pneumococcal promoter -10 (5'-TATACT-3') and -35 (5'-TTGAAC-3') boxes separated by 17 bp were identified 7 bp upstream of the start site. Analysis of the predicted secondary structure of the 327 5' region identified four pairs of inverted repeats R1-R8 predicted to fold into stem-loops, a small leader peptide [MTASMRLR, (Mef(E)L)] required for macrolide induction and a Rho-independent transcription terminator. RNA-seq analyses provided confirmation of transcriptional attenuation. In addition, expression of mef(E)L was also influenced by mef(E)L-dependent mRNA stability. The regulatory region 5' of mef(E) was highly conserved in other mef/mel(msr)-containing elements including Tn1207.1 and the 5612IQ complex in pneumococci and Tn1207.3 in Group A streptococci, indicating a regulatory mechanism common to a wide variety of Gram-positive bacteria containing mef/mel(msr) elements.