Serotypes, Clones, and Mechanisms of Resistance of Erythromycin-Resistant Streptococcus pneumoniae Isolates Collected in Spain

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Abstract
The aim of this study was to analyze the distributions of antibiotic susceptibility patterns, serotypes, phenotypes, genotypes, and macrolide resistance genes among 125 nonduplicated erythromycin-resistant Streptococcus pneumoniae clinical isolates collected in a Spanish point prevalence study. The prevalence of resistance to macrolides in this study was 34.7%. Multiresistance (to three or more antimicrobials) was observed in 81.6% of these strains. Among 15 antimicrobials studied, cefotaxime, moxifloxacin, telithromycin, and quinupristin-dalfopristin were the most active drugs. The most frequent serotypes of erythromycin-resistant isolates were 19F (25%), 19A (17%), 6B (12%), 14 (10%), and 23F (10%). Of the 125 strains, 109 (87.2%) showed the MLS B phenotype [103 had the erm (B) gene and 6 had both erm (B) and mef (E) genes]. Sixteen (12.8%) strains showed the M phenotype [14 with mef (E) and 2 with mef (A)]. All isolates were tested by PCR for the presence of the int, xis, tnpR , and tnpA genes associated with conjugative transposons (Tn 916 family and Tn 917 ). Positive detection of erm (B), tet (M), int , and xis genes related to the Tn 916 family was found in 77.1% of MLS B phenotype strains. In 16 strains, only the tndX, erm (B), and tet (M) genes were detected, suggesting the presence of Tn 1116 , a transposon recently described for Streptococcus pyogenes . Five clones, namely, Sweden 15A -25, clone 19F ST87, Spain 23F -1, Spain 6B -2, and clone 19A ST276, accounted for half of the MLS B strains. In conclusion, the majority of erythromycin-resistant pneumococci isolated in Spain had the MLS B phenotype, belonged to multiresistant international clones, and carried the erm (B), tet (M), xis , and int genes, suggesting the spread of transposons of the Tn 916 family.

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