Comparative susceptibility to penicillin and quinolones of 1385 Streptococcus pneumoniae isolates

Antibiotic resistance among Streptococcus pneumoniae isolates has spread rapidly throughout the world since the first description of a strain with diminished susceptibility to penicillin in Australia in 1967. A total of 1385 strains of S. pneumoniae, collected in several centres throughout Austria, were assessed for their sensitivity to moxifloxacin, trovafloxacin, ciprofloxacin, ofloxacin, levofloxacin and lomefloxacin. The MICs were determined using the agar dilution method, according to NCCLS guidelines. Both moxifloxacin and trovafloxacin showed good anti-pneumococcal activity in terms of MIC50 (both 0.125 mg/L) and MIG(90) (both 0.25 mg/L). Less active, but with similar activity to each other, were ciprofroxacin and levofloxacin, each with an MIC50 of 1 mg/L and an MIG(90) of 2 mg/L. Ofloxacin showed only moderate activity (MIC50, 1 mg/L; MIC90, 2 mg/L) and lomefloxacin was the least active compound (MIC50, 4 mg/L; MIC90, 8 mg/L). Both moxifloxacin and trovafloxacin at a concentration of less than or equal to 0.5 mg/L inhibited all of the S. pneumoniae strains tested.