Changing antibiotic resistance pattern of serogroup 6 Streptococcus pneumoniae isolated from children with upper respiratory infection during the period from 1997 to 2007

Objective To investigate the serotypes and antimicrobial resistance of serogroup 6 Streptococcus pneumoniae (S.pneumoniae) isolated from children with upper respiratory infection in Beijing from 1997 to 2007. Methods The serogroup 6 and type 6A and 6B of the S.pneumoniae isolates were determined by the quellung reaction using antiserum. Serotype 6C was determined by the multi-bead assay. The minimum inhibitory concentration (MIC) was determined by E-test method for penicillin,amoxicillin-clavulanic acid,ceftriaxone,cefuroxime,erythromycin,imipenem,vancomycin and levofloxacin. Results A total of 893 S. pneumoniae strains were isolated from 1997 to 2007,and 119 (13.3%) strains were identified as serogroup 6. The number (proportion) of type 6A,6B and 6C were 71 (59.7%),39 (32.7%) and 9 (7.6%),respectively. The non-susceptibility rate to penicillin,cefuroxime and erythromycin increased from 3.4%,1.7% and 86.2% during 1997—2000 to 29.4%,23.5% and 100% during 2005—2007,respectively. The values of MIC 90 and the maximum value of MIC of the three antibiotics also increased. The non-susceptibility rate of type 6A,6B and 6C to penicillin was 7.2%,24.3% and 0,respectively. Conclusions Type 6A was the main type of serogroup 6 S. pneumoniae isolated from children in Beijing. The recently reported type 6C can be found,but less frequently than other types. The resistance of serogroup 6 S. pneumoniae to β-lactams and macrolide antibiotics is more common than before. Type 6B is more resistant than type 6A and 6C.