Macrolide resistance mechanisms in serotypes of Streptococcus pneumoniae

Abstract number: P996

Background:Streptococcus pneumoniae is an important pathogen that causes severe life-threatening illnesses in the elderly and children. Increases in macrolide resistance in S. pneumoniae clinical isolates have significant clinical implications. The most common mechanisms of macrolide resistance are methylation of the ribosomal target site (encoded by the ermB gene) and drug efflux (encoded by the mefA or the mefE gene). The aim of this study was to characterize these mechanisms in various serotypes of S. pneumoniae in order to understand the relationship between macrolide resistance and capsular serotypes.

Methods: 465 macrolide-resistant (erythromycin MIC 1 mg/L) clinical S. pneumoniae isolates, collected through the Tigecycline Evaluation and Surveillance Trial (T.E.S.T.), were evaluated. Detection of genes involved in macrolide resistance (ermB, mefA and mefE) and serotyping were performed by multiplex-PCR.

Results: 54% of the isolates tested were from North America, 27% from Europe with the remainder (19%) from other continents. Among these 465 strains, the most prevalent pneumococcal macrolide resistance genotypes were mefE/A (42%) and ermB (37%) followed by ermB+mefE (18%) and then other mechanisms (3%). The most prevalent serogroup was 19 (34%) and 6 (17%).

Among ermB+mefE-positive isolates, 84% were serogroup 19 while only 21% were serogroup 19 among ermB-positive isolates. Among mefE/A-positive isolates, only 25% were serogroup 19 and the remaining were other serotypes. High-level resistance (MLSB phenotype) was associated with serogroup 19 while lower-level resistance (M phenotype) was associated with other serotypes.

Conclusions: This study confirms that certain capsular serotypes are associated with macrolide resistance and confirms also the predominance of high-level macrolide resistance among serogroup 19. These findings emphasize the need for continuous worldwide monitoring of macrolide-resistance and serotypes among S. pneumoniae.