The mef encoded efflux pump conferring low-level macrolide resistance (M phenotype) is more prevalent in other Asian and European countries and North America [9, 14–16]. S. pneumoniae clones carrying both genes (dual-positive) have emerged as important clinical populations. These strains have serotypes not covered by the heptavalent pneumococcal conjugate vaccine (PCV7) released in 2000 and are multidrug resistant, posing a significant health threat. [9, 10, 15, 17, 18]. These dual-positive S. pneumoniae strains now comprise a substantial portion of macrolide resistant

isolates in regions across the globe [6, 7, 9, 11, 19]. A primary vehicle for lateral transfer of both genes is Tn2010, a transposon LGK-974 of the tetracycline resistance gene tet(M)-carrying Tn916 family with an inserted erm(B) element and mef(E)-containing mega element [20]. A second transposon carrying both erm(B)and mef(E), Tn2017, comprised of Tn916 with the erm(B)-carrying Tn917 and the mega element inserted, was found in a Hungarian isolate from 2003 [21]. Tn916-family transposons with various insertions are the basis of most erm(B)-carrying mobile genetic elements, while mef(E) is known to be only in variants of the mega element [20].

In this study, we characterize a set of macrolide resistant S. pneumoniae clinical isolates collected in Arizona based on mef(E) and erm(B) gene presence, multilocus

sequence typing (MLST) and serotyping, selleck products antibiotic susceptibility profiles, and potential transposon carriage. We document Racecadotril likely episodes of capsule switching and serotype replacement, both mechanisms that allow S. pneumoniae to evade the PCV7 and cause infection in an immunized population. Methods Bacterial isolates From 1999 to 2008, 592 S. pneumoniae isolates were collected by a large hospital reference laboratory that receives specimens from ten system-wide medical centers and a high volume private reference laboratory that receives specimens from regional inpatient, long-term care, and outpatient facilities. Isolates considered non-invasive were obtained from upper respiratory tract (upper respiratory specimens plus sinus, nasal, and nasopharyngeal swabs), lower respiratory tract, ear, eye, body fluid, wound, and tissue (n = 488). Isolates considered invasive were obtained from blood (n = 100), urine (n = 2), and cerebrospinal fluid (CSF, n = 2) specimens. All were identified by bile solubility and optochin susceptibility testing. Patients ranged in age from 1 month to 88 years with a median age of 19 years and mean age of 29 1/2years.