In vitro effects of penicillin and telithromycin on the expression of Streptococcus pneumoniae capsule

OBJECTIVE: To evaluate the effects of subinhibitory concentrations of penicillin and telithromycin on capsular formation by Streptococcus pneumoniae. METHODS: A total of 60 isolates of S. pneumoniae, 20 susceptible, 20 intermediately resistant and 20 resistant to penicillin, were studied. All isolates were susceptible to telithromycin. RESULTS: All isolates were capsulate when grown without antibiotics. Encapsulation was lower after incubation with telithromycin as compared with penicillin in isolates susceptible to penicillin (20% versus 75%), in those intermediately resistant to penicillin (25% versus 95%) and in isolates fully resistant to penicillin (15% versus 100%) (P < 0.01). CONCLUSIONS: Telithromycin appears to be superior to penicillin in reducing the expression of the capsule by S. pneumoniae.