Antibiotic susceptibility of clinical isolates of Streptococcus pneumoniae

Ninety-three representative, recent clinical isolates of Streptococcus pneumoniae were examined for susceptibility to 9 antimicrobial drugs utilizing Mueller-Hinton agar (MHA) enriched with sheep blood and a hypercapnic atmosphere of incubation, One isolate was resistant to penicillin G (minimum inhibitory concentration, MIC = 2 mu g/ml) and 6 isolates were of intermediate susceptibility to penicillin G (MICs = 0.125-0.25 mu g/ml). The penicillin-G-resistant isolate was also resistant to cefuroxime (MIG = 4 mu g/ml) and of intermediate susceptibility tu cefotaxime (MIG = 1 mu g/ml). This isolate was resistant to chloramphenicol (MIG = 16 mu g/ml) as well. All 93 isolates were susceptible to teicoplanin and vancomycin. Two isolates each were resistant (MICs = 16 mu g/ml) or moderately susceptible (MICs = 8 mu g/ml) to chloramphenicol. Eight isolates were resistant to doxycycline (MICs greater than or equal to 8 mu g/ml), whereas 2 isolates were of intermediate susceptibility to this antibiotic (MICs = 4 mu g/ml). Three isolates were resistant to erythromycin (MICs greater than or equal to 4 mu g/ml), and 2 isolates showed reduced susceptibility to erythromycin (MICs = 2 mu g/ml). Chocolatized MHA antagonized the activity of teicoplanin and vancomycin against pneumococcal isolates. Haemophilus test and Wilkins-Chalgren media failed to support optimal growth of all pneumococcal isolates.