Penicillin-resistant Streptococcus pneumoniae in Riyadh, Saudi Arabia.

During a period of ten months, minimum inhibitory concentrations (MICs) to seven antimicrobial agents of 150 clinical isolates of Streptococcus pneumoniae were determined at a teaching hospital in Riyadh, Saudi Arabia. Twenty-two (14.7%) isolates showed relative resistance to penicillin. High-level resistance to penicillin was not observed in any of the isolate. Seventeen (11.3%) isolates were resistant to erythromycin, and 31 (20.7%) to tetracycline. Multiple resistance was observed in 21 (14%) isolates. Decreased resistance to ceftriaxone was also found in two (1.3%) isolates. Isolates with relative resistance to penicillin were significantly associated with higher rates of resistance to other antibiotics than were penicillin-susceptible isolates. This was also true for multiple resistance encountered in both groups.