Fluoroquinolone resistance is a poor surrogate marker for type II topoisomerase mutations in clinical isolates of Streptococcus pneumoniae

The association between fluoroquinolone susceptibility and DNA mutations coding for amino acid substitutions in the quinolone resistance-determining region was assessed with 44 clinical isolates of Streptococcus pneumoniae. Twenty-three strains bore at least one amino acid substitution. Only seven strains with mutations were suggested by diminished susceptibility to ciprofloxacin (MIC, ≥2 μg/ml).