CLONING AND CHARACTERIZATION OF A NOVEL MACROLIDE EFFLUX GENE, MREA, FROM STREPTOCOCCUS-AGALACTIAE

A strain of Streptococcus agalactiae displayed resistance to 14-, 15-, and 16-membered macrolides. In PCR assays, total genomic DNA from thi s strain contained neither erm nor mef genes. EcoRI-digested genomic D NA from this strain was cloned into lambda Zap II to construct a libra ry of S. agalactiae genomic DNA. A clone, pAES63, expressing resistanc e to erythromycin, azithromycin, and spiramycin in Escherichia coli wa s recovered. Deletion derivatives of pAES63 which defined a functional region on this clone that encoded resistance to 14- and 15-membered, but not 16-membered, macrolides were produced. Studies that determined the level of incorporation of radiolabelled erythromycin into E. coli were consistent with the presence of a macrolide efflux determinant. This putative efflux determinant was distinct from the recently descri bed Mef pump in Streptococcus pyogenes and Streptococcus pneumoniae an d from the multicomponent MsrA Pump in Staphylococcus aureus and coagu lase-negative staphylococci. Its gene has been designated mreA (for ma crolide resistance efflux).