Drug Susceptibility of Streptococcus pneumoniae Strains Isolated in Tehran, Iran

Background – The emergence and spread of penicillin and multidrug resistance in Streptococcus pneumoniae has become a major concern worldwide. Consequently, clinical laboratories should consider screening-selected isolates to determine whether they are susceptible to cefotaxime as well as to penicillin. The aim of this study was to survey drug resistance among clinically important isolates of S. pneumoniae recovered from patients in Tehran.Methods – The drug susceptibility of 130 isolates of S. pneumoniae cultured from severely infected patients from 1998 to 2000 was determined using both agar disk diffusion and macro broth dilution tests. Isolates were grown from clinical specimens including blood (60%) and cerebrospinal fluid (20%) from patients with pneumonia, bacteremia or meningitis. The remaining isolates were recovered from sputa (10%) and sinus exudates. Bacterial cultures were sent to Pasteur Institute for conformational and drug susceptibility tests. Results – Sixty-eight percent of isolates were resistant to penicillin, 10% to erythromycin, 52% to cotrimoxazole, and 56% to tetracycline. Of the 25% of the organisms that were found to be resistant to cefotaxime, 1% were highly resistant. None of the isolates were resistant to vancomycin. The minimum inhibitory concentrations (MICs) of cefotaxime corresponded to the MICs of penicillin (being the same or different by only 1 or 2 dilutions).Conclusion – Resistance to penicillin and cefotaxime increased over the study period. Penicillin-resistant strains of S. pneumoniae cultured from patients in Tehran were also more likely to be resistant to other beta-lactams such as cefotaxime. The increasing trend of antibiotic resistance among strains of S. pneumoniae in Iran is alarming, and the treatment of infections with this organism will be more difficult in the future.