Only one MLST allele is common to both populations. Despite MLST dissimilarity among the

erm(B)-positive isolates, all have similar antibiotic susceptibility profiles. Most are intermediately or fully susceptible to penicillin and trimethoprim-sulfamethoxazole #Erastin randurls[1|1|,|CHEM1|]# while resistant to erythromycin and clindamycin, and all carry tet(M). Out of the 13 isolates in this population, all eight ST63 isolates were negative for int, xis, tnpR, and tnpA; the genetic context of their antibiotic resistance genes remains unknown. Two isolates, one ST3066 and a non-typed isolate, tested positive for Tn916 and Tn917, and produced an 800 bp PCR product with J12/J11 primers, signifying

the presence of Tn3872. The two ST315 isolates and the ST180 isolate tested positive for Tn916, but were negative for MLN0128 Tn917 and with J12/J11, possibly indicating carriage of tet(M) in Tn916 and a separate erm(B) element (Table 3). Genotype analyses of the mef(E)-positive population show high diversity with relatively even distribution. Besides three sets of SLVs, the highest number of MLST alleles shared by any two sequence types is three, and no more than

four isolates of the same sequence type were identified. Many different antibiotic susceptibility profiles were identified in this population, with no single dominant profile. Of the 44 mef(E)-positive isolates, eight isolates of three sequence types, ST236, a SLV of ST236, and ST3280, were positive for int and xis, for the SG1/LTf region, and for tet(M), indicating the presence of Tn2009. Five others were positive for Progesterone only int and xis and tet(M), indicating carriage of Tn916 and a separate mega element. The absence of these transposon PCR targets and tet(M) in the other 31 isolates suggests they are carrying the mega element (Table 3). Discussion Macrolide resistance rates in clinical isolates of S. pneumoniae vary greatly among countries. The rate in our collection of isolates from Arizona patients, 23.6%, is consistent with other studies targeting S. pneumoniae in North America [15, 38].