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 micrograms/ml) and 6 isolates were of intermediate susceptibility to penicillin G (MICs = 0.125-0.25 microgram/ml). The penicillin-G-resistant isolate was also resistant to cefuroxime (MIC = 4 micrograms/ml) and of intermediate susceptibility to cefotaxime (MIC = 1 microgram/ml). This isolate was resistant to chloramphenicol (MIC = 16 micrograms/ml) as well. All 93 isolates were susceptible to teicoplanin and vancomycin. Two isolates each were resistant (MICs = 16 micrograms/ml) or moderately susceptible (MICs = 8 micrograms/ml) to chloramphenicol. Eight isolates were resistant to doxycycline (MICs > or = 8 micrograms/ml), whereas 2 isolates were of intermediate susceptibility to this antibiotic (MICs = 4 micrograms/ml). Three isolates were resistant to erythromycin (MICs > or = 4 micrograms/ml), and 2 isolates showed reduced susceptibility to erythromycin (MICs = 2 micrograms/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.