Fluoroquinolone resistance in Streptococcus pneumoniae: evidence that gyrA mutations arise at a lower rate and that mutation in gyrA or parC predisposes to further mutation.

Fluoroquinolones are being increasingly used for acute lower respiratory tract infection where Streptococcus pneumoniae is the most important bacterial pathogen. S. pneumoniae becomes resistant to quinolone antibiotics by mutations in a small section of the parC and gyrA genes.