ABSTRACT
Streptococcus pneumoniae isolates from blood, CSF, respiratory tract and other clinical specimens from 626 patients were tested for sensitivity to penicillin. The bacteria were collected from patients in different hospitals in Riyadh, Saudi Arabia. Using 1 micro g oxacillin disk, 147 [23.5%] of these isolates were found to be relatively resistant to penicillin [RPR]. When 358 pneumococcal isolates were tested for RPR using 1 or 10 unit penicillin disks and compared with the MIC or oxacillin disk, as many as 18% were incorrectly designated as sensitive by penicillin disks. Since pneumococci can cause potentially life threatening infections like meningitis, septicemia and pneumonia, the significance of determining their correct susceptibility to penicillin cannot be over emphasized