Antimicrobial susceptibilities and distribution of resistance genes for β-lactams and macrolides in Streptococcus pneumoniae isolated between 2002 and 2004 in Tokyo

Antimicrobial susceptibilities of 205 Streptococcus pneumoniae strains isolated between 2002 and 2004 in Japan were examined and the distribution of genes for resistance to penicillins and macrolides were investigated by polymerase chain reaction. The molecular epidemiology of 92 randomly selected isolates was also examined by pulsed-field gel electrophoresis (PFGE). The numbers of S. pneumoniae isolates resistant to benzylpenicillin, clarithromycin and tetracycline were, respectively, 39 (19%), 111 (54%) and 155 (76%), and the numbers increased annually. All isolates were susceptible to amoxicillin, fluoroquinolones, vancomycin and linezolid. Analysis of mutations in the genes for penicillin-binding protein showed that 92% of isolates had mutations in pbp1a, pbp2b and/or pbp2x. Susceptibility to benzylpenicillin decreased with increasing number of mutated pbp genes. The macrolide resistance genes ermB and mefA were found in 99 (48%) and 76 (37%) isolates, respectively. The presence of ermB was associated with high-level resistance to macrolides, and the percentage of isolates with ermB increased annually. The presence of mefA also increased with increasing number of mutated pbp genes. Although the 92 isolates belonged to 74 PFGE types, three groups with an 80% similarity in their PFGE patterns were found at high frequency. Two of the three groups contained no isolates susceptible to penicillin and/or tetracycline, and their percentages increased annually. Our results suggest that the number of S. pneumoniae isolates with reduced susceptibility due to accumulation of resistance genes has been increasing.