In vitro susceptibility to gemifloxacin and trovafloxacin of Streptococcuspneumoniae strains exhibiting decreased susceptibility to ciprofloxacin

The in vitro susceptibility to trovafloxacin and gemifloxacin of Streptococ cus pneumoniae strains exhibiting decreased susceptibility to ciprofloxacin (MIC greater than or equal to 2 mu g/ml; 30 strains with intermediate resi stance [MIC 2 mu g/ml] and 43 strains with complete resistance [MIC greater than or equal to 4 mu g/ml]) was determined, Seventy-three strains collect ed in a surveillance study carried out from May 1996 to April 1997 in Spain (prior to commercialisation of trovafloxacin and gemifloxacin) from patien ts with respiratory tract infections were tested. The antibacterial activit y of gemifloxacin was affected to a lesser extent than that of trovafloxaci n by the increase in the MIC of ciprofloxacin, with gemifloxacin showing si gnificantly (P less than or equal to 0.001) better antibacterial activity t han trovafloxacin in all ciprofloxacin MIC categories (MIC50/MIC90 values o f 0.015/0.03, 0.015/0.06, 0.03/ 0.06 and 0.12/0.25 mu g/ml for gemifloxacin vs 0.1210.12, 0.12/1, 0.25/0.5 and 2/4 mu g/ml for trovafloxacin in the 2, 4, 8 and greater than or equal to 16 mu g/ml ciprofloxacin MIC categories, respectively). Nine (12.3%) of these 73 strains exhibited decreased suscep tibility to trovafloxacin (greater than or equal to 2 mu g/ml), whereas all strains were inhibited by 0.25 mu g/ml of gemifloxacin.