Structure and dissemination of a chromosomal insertion element encoding macrolide efflux in Streptococcus pneumoniae

Macrolide resistance associated with macrolide efflux (mef) has rapidly inc reased in Streptococcus pneumoniae. We defined the genetic structure and di ssemination of a novel mefE-containing chromosomal insertion element. The m efE gene was found on the 5' end of a 5.5- or 5.4-kb insertion designated a s the macrolide efflux genetic assembly (mega), which is found in greater t han or equal to4 distinct sites of the pneumococcal genome. The element was transformable and conferred macrolide resistance to susceptible S. pneumon iae. The first 2 open-reading frames (ORFs) of the element formed an operon composed of mefE and a predicted adenosine triphosphate-binding cassette h omologous to msrA. Convergent to this efflux operon were 3 ORFs with homolo gy to stress response genes of Tn5252. Mega was related to the recently des cribed mefA-containing element Tn1207.1 but lacked the genes necessary for transposition and had unique termini and insertion sites. In metropolitan A tlanta, macrolide resistance due to mega rapidly increased in S. pneumoniae by clonal expansion and horizontally by transformation.