title: Alterations of gyrA, gyrB, and parC and Activity of Efflux Pump in Fluoroquinolone-resistant Acinetobacter baumannii.
abstract: OBJECTIVE
  This study investigated the fluoroquinolone-resistant mechanism of 56 clinical cases of A baumannii infection from 23 non-tertiary hospitals, collected between 2004 and 2006.
  
  
  METHODS
  Susceptibility testing was performed by broth microdilution and Epsilometer test. Analyses of quinolone resistance-determining region (QRDR) were done by sequencing. The activity of the efflux pump was measured using inhibitors.
  
  
  RESULTS
  The sequences from selected 56 isolates were divided into seven groups (I-VII) on the basis of mutations in gyrA (S83L), parC (S80L, S80W and S84K) and gyrB (containing the novel mutations E679D, D644Y and A677V). The 27 isolates with triple mutations in gyrA, gyrB and parC (groups IV-VII) showed higher levels of resistance to ciprofloxacin (minimal inhibitory concentration [MIC] of 16-256 μg/mL) than the 26 isolates with double mutations in gyrA and parC (groups II and III, MIC of 8-64 μ g/mL; p < 0.05). Alterations in the efflux pump were observed in four isolates with the parC S80L mutation (group II) or E84K mutation (group VII), but no effect was observed in an isolate with the parC S80 W mutation (group III).
  
  
  CONCLUSIONS
  These results suggest that triple mutations in clinical isolates of A baumannii contribute to the development of high levels of resistance to fluoroquinolones and that mutations in parC S80L or E84K (groups II and VII) may contribute to alterations in efflux pump activity in A baumannii.
authors.affiliation: Division of Antimicrobial Resistance, Korea National Institute of Health, Osong, Korea.
authors.forename: Sunok
authors.initials: S
authors.lastname: Park
authors.forename: Kyeong Min
authors.initials: KM
authors.lastname: Lee
authors.forename: Yong Sun
authors.initials: YS
authors.lastname: Yoo
authors.forename: Jung Sik
authors.initials: JS
authors.lastname: Yoo
authors.forename: Jae Il
authors.initials: JI
authors.lastname: Yoo
authors.forename: Hwa Su
authors.initials: HS
authors.lastname: Kim
authors.forename: Yeong Seon
authors.initials: YS
authors.lastname: Lee
authors.forename: Gyung Tae
authors.initials: GT
authors.lastname: Chung
keywords: A baumannii; efflux pump fluoroquinolone resistance; gyrA; gyrB; parC