Prevalence and molecular genetics of macrolide resistance among Streptococcus pneumoniae isolates collected in Finland in 2002

Abstract

The prevalence and mechanisms of macrolide resistance among 1,007 clinical pneumococcal isolates collected in Finland were investigated. Of these, 217 (21.5%) were resistant to erythromycin and 11% to clindamycin. Among the erythromycin-resistant isolates, mef(E) was present in 95 isolates (44%), mef(A) was present in 12 isolates (6%), and erm(B) was present in 90 isolates (41%). A double mechanism, mef(E) and erm(B), was detected in five isolates (2%). Ribosomal mutation was detected in 14 (6%) macrolide-resistant isolates in which no other determinant was found. Based on the telithromycin MICs, two groups of isolates were formed: 83.3% of the isolates belonged to a major group for which the telithromycin MIC range was < or =0.008 to 0.063 microg/ml, and 16.7% belonged to a minor group for which the telithromycin MIC range was 0.125 to 8 microg/ml. All except three isolates in the minor population carried a macrolide resistance gene.

FIG. 1.

Distribution of telithromycin MICs of macrolide-susceptible and -resistant pneumococci harboring a macrolide resistance mechanism. Of the susceptible pneumococci, 41 isolates were randomly tested for the presence of a macrolide resistance determinant; none of them carried any macrolide resistance mechanism. Bars with slashes, isolates susceptible to erythromycin and azithromycin (n = 787); gray bars, isolates with mutations or undetermined mechanism (n = 17); spotted bars, isolates with mef(A) or mef(E) (n = 107); black bars, isolates with erm(B) or erm(TR) (n = 91); white bars, isolates with double mechanism erm(B) and mef(E) (n = 5).