We analyzed Streptococcus pneumoniae isolates from the bloodstream between April 2005 and February 2007. We analyzed isolates of 28 strains from medical facilities in Gifu prefecture to determine antibiotic susceptibility, genotype of penicillin-binding protein (PBP) genes and macrolide resistant genes. We also assessed the efficacy of respiratory quinolones using Monte Carlo simulation. Garenoxacin (GRNX) and moxifloxacin (MFLX) showed the lowest MIC₉₀ value of 0.125𝜇g/mL, followed by MIC₉₀ of imipenem (IPM) of 0.25𝜇g/mL and tosufloxacin (TFLX), MIC₉₀ of meropenem (MEPM) and vancomycin (VCM) of 0.5𝜇g/mL. Twenty-two strains possessed at least one mutation in PBP-encoding genes pbp1a, pbp2x or pbp2b and seven strains possessed all three mutant alleles. Twenty-two strains possessed either of macrolide resistant genes ermB or mefA, and one strain possessed both. On efficacy assessment, we calculated the probability of target attainment for free-drug area under the curve (fAUC)/MIC ratio (fAUC/MIC). GRNX and MFLX showed a probability of 90% or more at fAUC/MIC of 30 and 125, each considered effective against Gram-positive bacteria and suppression of resistance development, furthermore, GRNX showed a probability of 89.7% at fAUC/MIC of 250.

The antibacterial susceptibility to frequently prescribed antibiotics of Streptococcus pneumoniae isolated from the pediatric patients with acute respiratory infectious diseases was investigated in a study of three medical institutions in Korea. Total 143 clinical isolates of S. pneumoniae were available for susceptibility tests between May 2003 and July 2007. Antimicrobial susceptibility data for S. pneumoniae were analyzed by using agents of amoxicillin, cefaclor, cefuroxime, cefdinir, and cefditoren as the test antibiotics.The prevalence of each resistance class, penicillin-resistant S. pneumoniae (PRSP) were high with the proportion of MIC range (susceptible=8.4%, intermediate resistance=18.2%, resistance=73.4%). MIC₉₀ and susceptible (S) rate of antimicrobialagents to the strains tested were amoxicillin (MIC₉₀=4𝜇g/ml, S=76.2%), cefaclor(MIC₉₀=128𝜇g/ml, S=8.4%), cefuroxime (MIC₉₀=16𝜇g/ml, S=24.5%), cefdinir(MIC₉₀=16𝜇g/ml, S=21.8%), and cefditoren (MIC₉₀=0.5𝜇g/ml, S=90.2%) respectively.Against clinical isolates including PRSP, cefditoren demonstrated the strongest antibacterial activity intrinsically among the antibiotics tested. Conclusively, the antimicrobial activity of cefditoren to S. pneumoniae strains isolated from pediatric patients with acute respiratory infection is very high. In South Korea, where the antibiotic resistance of S. pneumoniae is issued, cefditoren is expected to be used as a primary or secondary antibiotic. Moreover, cefditoren may serve as a useful option for secondary antibiotics after failure of amoxicillin treatment, which is most primarily used for acute respiratory S. pneumoniae infection in children.