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

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 (Tn916 family and Tn917). Positive detection of erm(B), tet(M), int, and xis genes related to the Tn916 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 Tn1116, 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 Tn916 family.