[The phenotype and genotype patterns of erythromycin-resistant Streptococcus pneumoniae].

OBJECTIVE

To investigate the resistance phenotypes and genotypes in erythromycin-resistant Streptococcus (S.) pneumoniae.

METHODS

The minimum inhibitory concentration (MIC) of erythromycin, clindamycin, penicillin and fluoroquinolones against 192 strains of S. pneumoniae was tested with broth microdilution method according to the guidelines of the National Committee for Clinical Laboratory Standards. Of 148 clinical isolates of erythromycin resistant S. pneumoniae, the macrolide resistance phenotypes were observed by the erythromycin-clindamycin-spiramycin triple-disc test and erythromycin resistance genes were detected by polymerase chain reaction.

RESULTS

42.7% S. pneumoniae isolates was resistant (intermediate and resistant) to penicillin while the resistance rates to erythromycin and clindamycin were 77.6% and 66.7% respectively. The ermB gene, being the most prevalent, was detected in 79.1% of the 148 erythromycin-resistant strains. The main phenotype (85.1%) of erythromycin-resistant strains was constitutive macrolide, lincosamide, and streptogramin B resistance phenotype (cMLS). Erythromycin MICs for S. pneumoniae ermB-positive isolates were higher than those for mefA-positive isolates. 74.4% of the ermB-positive isolates demonstrated erythromycin MICs of > 16.0 micro g/ml, and the erythromycin MICs for mefA-positive isolates ranged from 0.5 approximately 4.0 micro g/ml.

CONCLUSIONS

The resistance rate of S. pneumoniae to erythromycin is high in China. The main phenotype is cMLS. Ribosomal modification (ermB gene coded) is the main resistance mechanism against erythromycin in S. pneumoniae