Antimicrobial susceptibilities of 1,684 Streptococcus pneumoniae and 2,039Streptococcus pyogenes isolates and their ecological relationships: Results of a 1-year (1998-1999) multicenter surveillance study in Spain

A nationwide multicenter susceptibility surveillance study which included 1 ,684 Streptococcus pneumoniae and 2,039 S. pyogenes isolates was carried ou t over 1 year in order to assess the current resistance patterns for the tw o most important gram-positive microorganisms responsible for community-acq uired infections in Spain. Susceptibility testing was done by a broth micro dilution method according to National Committee for Clinical Laboratory Sta ndards M100-S10 interpretative criteria. For S. pneumoniae, the prevalences of highly resistant strains were 5% for amoxicillin and amoxicillin-clavul anic acid; 7% for cefotaxime; 22% for penicillin; 31% for cefuroxime; 35% f or erythromycin, clarithromycin, and azithromycin; and 42% for cefaclor. Fo r S. pyogenes, the prevalence of erythromycin resistance was 20%. Efflux wa s encountered in 90% of S. pyogenes and 5% of S. pneumoniae isolates that e xhibited erythromycin resistance. Erythromycin resistance was associated wi th clarithromycin and azithromycin in both species, regardless of phenotype . Despite the different nature of the mechanisms of resistance, a positive correlation (r = 0.612) between the two species in the prevalence of erythr omycin resistance was found in site-by-site comparisons, suggesting some ki nd of link with antibiotic consumption. Regarding ciprofloxacin, the MIC wa s greater than or equal to 4 mug/ml for 7% of S. pneumoniae and 3.5% of S. pyogenes isolates. Ciprofloxacin resistance (MIC, greater than or equal to 4 mug/ml) was significantly (P < 0.05) associated with macrolide resistance in both S. pyogenes and S. pneumoniae and with penicillin nonsusceptibilit y in S. pneumoniae.