Single and double mutations in gyrA but not in gyrB are associated with low- and high-level fluoroquinolone resistance in Helicobacter pylori.

In one French hospital the rate of resistance to ciprofloxacin in Helicobacter pylori was 3.3% (2 of 60 strains) in 1999. The six resistant clinical strains (four from 1996 and two from 1999) and three ciprofloxacin-selected single-step mutants studied carried one gyrA mutation but none in gyrB. Clinafloxacin and garenoxacin were the most active fluoroquinolones against these mutants. Occurrence of a second gyrA mutation was associated with high MICs of all fluoroquinolones tested.