Increase in erythromycin-resistant Streptococcus pneumoniae in Colombia, 1994-2008

Introduction. Streptococcus pneumoniae is a commonly implicated agent in invasive disease. For infections of S. pneumoniae resistant to beta-lactam. macrolides are an alternative treatment. However, resistance to macrolides has increased worldwide as well. Objective. The frequency of resistance to erythromycin was determined for S. pneumoniae over a 15-year surveillance period, and the resistant isolates were characterized phenotypically and genotypically. Materials and methods. Demographic data of the patients, antimicrobial susceptibility and serotypes were analyzed for 3,241 S. pneumoniae isolates recovered between 1994 and 2008. The phenotypes were determined by the double-disc technique and genotypes by PCR (polymerase chain reaction) and PFGE (pulsed field gel electrophoresis). Isolates were recovered from invasive diseases and were provided by national public health laboratories. Results. Of the 3,241 isolates, 136 were resistant to erythromycin. In the 12-year period between 19941996 and 2006-2008, resistance in each 2-year sampling had increased from 2.4% to 6.9% in children under 6 years and from 3.3% to 5.7% in adults. The most common serotypes were 6B (36.8%). 14 (16.9%) and 6A (17.6%). Constitutive phenotype cMLSB was determined in 87 isolates; 82 of these expressed the ermB gene. Phenotype M was determined in 46 isolates; 45 had the mefA gene. An additional three isolates expressed the inducible phenotype (iMLS(B)), and one expressed the ermB gene. By PFGE, 50 of the isolates were found to be related to international clones-58% were Spain(6B)-ST90, 26% Spain(9V)-ST156, 8% Colombia(23F)-ST338 and 8% Spain(23F)-ST81. Conclusion. The increase in erythromycin resistance was primarily related to the mechanism of ribosomal methylation. More than half the cases were congeneric with the clone Spain(6B)-ST90 that has been circulating in Colombia since 1994.