Molecular characterization of PBP2b in clinical isolates of Streptococcus pneumoniae

Streptococcus pneumoniae is one of the most important bacterial pathogens associated with pneumonia, meningitis, sinusitis, and otitis media. β-Lactam resistance in clinical S.pneumoniae strains is mediated by altered PBPs, specifically PBP2b. The purpose of this study was to determine the rates of penicillin and other antibiotics resistance in clinical strains of S. pneumoniae and to analyze possible mutations in pbp2b. Susceptibility testing was done by disc diffusion method for oxacillin, erythromycin, cefotaxime, cotrimoxazole, ampicillin, vancomycin and tetracycline. MIC was determined by broth micro dilution method for penicillin. Pbp2b gene was amplified by PCR and sequenced. From all 54 isolates, 44.4% (24 isolates) were penicillin intermediate, 25.9% (14 isolates) werepenicillin resistant, 51.9% (28 isolates) were cotrimoxazole resistant, 16.6% (9 isolates) were erythromycin resistant, 3.7% (2 isolates) were Cefotaxime resistant, and 18.51% (10 isolates) were tetracycline resistant. All penicillin resistant and the most penicillin intermediate resistant isolates had mutations in catalytic regions of PBP2b. Our results showed the increase of penicillin resistance in S. pneumoniae isolates, however prevalence of multiple resistant strains revealed a crisis in treatment of pneumococcal infections. Our investigation demonstrates that alterations in PBP2b tended to parallel with reduced susceptibility to penicillin. We have shown that susceptibility of S. pneumoniae to β-Lactams can generally be estimated by determining alterations in pbp2b gene.