Susceptibility of Streptococcus pneumoniae to non β-lactam antibiotics by serotype

Objective To investigate the susceptibility of Streptococcus pneumoniae to non β-lactam antibiotics by serotype. Methods The 625 strains were isolated from out-patients with upper respiratory infection in Beijing, Shanghai and Guangzhou, 2000-2002. Antibiotic susceptibility was determined by E-test for erythromycin and penicillin and by disk diffusion method for tetracycline, sulfamethoxazole-trimethoprim and chloramphenicol. Results A total of 625 pneumococal strains were typed. The common types were serotypes 19, 23, 6 and 14. The nonsusceptible rates to erythromycin, tetracycline or sulfamethoxazole-trimethoprim in common-type group were significantly higher than in the other types and nontypable group. Nonsusceptible rates of penicillin nonsusceptible S. pneumoniae (PNSP) to erythromycin and sulfamethoxazole-trimethoprim were significantly higher than those of penicillin susceptible S. pneumoniae (PSSP). In the nontypable group, nonsusceptible rates of PNSP to erythromycin and sulfamethoxazole-trimethoprim were also significantly higher than those of PSSP. Meanwhile, nonsusceptible rates of PNSP to erythromycin and tetracycline were significantly higher than those of PSSP in serotype 19; while the resistant rate to chloramphenicol was significantly lower. No similar association was found in serotype 23, 6 or 14. Conclusions The resistance rates to erythromycin, tetracycline and sulfamethoxazole-trimethoprim are very high for serotypes 19, 23, 6 and 14 pneumococcal strains. The difference of nonsusceptibility rates to some non β-lactam antibiotics between PNSP and PSSP may be influenced by serotype distribution.