In Vitro Activities of Fluoroquinolones against Antibiotic-Resistant Blood Culture Isolates of Viridans Group Streptococci from across Canada

Among 418 blood culture isolates of viridans group streptococci obtained between 1995 and 1997, the in vitro rates of nonsusceptibility to penicillin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole were 28, 29, 24, and 14%, respectively. The most prevalent group (125 strains) was Streptococcus mitis, followed by Streptococcus sanguis (56 strains). For 236 (56%) strains resistant to one or more antibiotics, the ciprofloxacin MIC at which 90% of the isolates were inhibited (MIC(90)) was 4 μg/ml, whereas the MIC(90)s of trovafloxacin, grepafloxacin, and gatifloxacin were 0.25 μg/ml.