Sensitivity and specificity of the PCR assay. (A) Specificity of the PCR-based assay. PCR tests were conducted with 25 pg of purified DNA from the organisms. Purified S. pneumoniae DNA was used for the positive control. Lanes: 1, molecular size marker; 2, S. pneumoniae; 3, Staphylococcus aureus; 4, Streptococcus mitis; 5, group A Streptococcus; 6, Escherichia coli; 7, Enterococcus faecalis; 8, Pseudomonas aeruginosa; 9, Salmonella group D; 10, H. influenzae; 11, Moraxella catarrhalis. (B) Agarose gel electrophoresis of PCR-amplified products from a 10-fold dilution of purified S. pneumoniae DNA. Lane 1, molecular size marker; lanes 2 to 8, dilution series from 10 ng to 10 fg of DNA (corresponding to 106 to 1 CFU/ml); lane 9, negative control. (C) Agarose gel electrophoresis of PCR-amplified products from culture-positive CSF or blood before and after antibiotic treatment. Lane 1, molecular size marker; lanes 2 to 5, samples from culture-positive CSF and blood before (lanes 2 and 4, respectively) and after (lanes 3 and 5, respectively) antibiotic treatment for 48 h; lane 6, positive control (S. pneumoniae DNA); lane 7, negative control (H2O).