In vitro activity of telithromycin against Spanish Streptococcus pneumoniae isolates with characterized macrolide resistance mechanisms

The susceptibilities to telithromycin of 203 Streptococcus pneumoniae isola tes prospectively collected during 1999 and 2000 front 14 different geograp hical areas in Spain were tested and compared with those to erythromycin A, clindamycin, quinupristin-dalfopristin, penicillin G, cefotaxime, and levo floxacin. Telithromycin was active against 98.9% of isolates (MICs, less th an or equal to0.5 mug/ml), with MICs at which 90% of isolates are inhibited being 0.06 mug/ml, irrespective of the resistance genotype. The correspond ing values for erythromycin were 61.0% (MICs, less than or equal to0.25 mug /ml) and > 64 mug/ml. The erm(B) gene (macrolide-lincosamide-streptogramin B resistance phenotype) was detected in 36.4% (n = 74) of the isolates, whi ch corresponded to 93.6% of erythromycin-intermediate and -resistant isolat es, whereas the mef(A) gene (M phenotype [resistance to erythromycin and su sceptibility to clindamycin and spiramycin without blunting]) was present i n only 2.4% (it = 5) of the isolates. One of the latter isolates also carri ed erm(B). Interestingly, in one isolate for which the erythromycin MIC was 2 mug/ml, none of these resistance genes could be detected. Erythromycin M ICs for S. pneumoniae crm(B)-positive isolates were higher (range, 0.5 to > 64 mug/ml) than those for erm(B)- and mef(A) -negative isolates (range, 0. 008 to 2 mug/ml). The corresponding values for telithromycin were lower for both groups, with ranges of 0.004 to 1 and 0.002 to 0.06 mug/ml, respectiv ely. The erythromycin MIC was high for a large number of erm (B) -positive isolates, but the telithromycin MIC was low for these isolates. These resul ts indicate the potential usefulness of telithromycin for the treatment of infections caused by erythromycin-susceptible and -resistant S. pneumoniae isolates when macrolides are indicated.