Mutations in the gyrA and parC genes associated with fluoroquinolone resistance in clinical isolates of Citrobacter freundii.

We determined partial sequences of the gyrA and parC genes of Citrobacter freundii type strain, and then examined 38 C. freundii clinical strains isolated from patients with urinary tract infections for the association of alterations in GyrA and ParC with susceptibility to fluoroquinolones. Our results suggest that in C. freundii DNA gyrase may be a primary target of quinolones, that an amino acid change at Thr-83 or Asp-87 in GyrA is sufficient to decrease susceptibility to fluoroquinolones, and that accumulation of changes in GyrA with the simultaneous presence of an alteration at Ser-80 or Glu-84 in ParC may be associated with the development of high-level fluoroquinolone resistance in C. freundii clinical isolates.