Mutant Prevention Concentrations of Ciprofloxacin and Levofloxacin and Target Gene Mutations of Fluoroquinolones in Elizabethkingia anophelis.

Fluoroquinolones are potentially effective against Elizabethkingia anophelis. We investigated the MIC, mutant prevention concentration (MPC), and target gene mutations of fluoroquinolones in E. anophelis. Eighty-five E. anophelis isolates were collected from five hospitals in Taiwan. The MIC and MPC of ciprofloxacin and levofloxacin were examined for all E. anophelis except 17 isolates, in which ciprofloxacin MPC could not be determined due to drug precipitation caused by overly high drug concentration. Mutations in the quinolone resistance-determining regions of DNA gyrase (GyrA and GyrB) and topoisomerase IV (ParC and ParE) in the clinical isolates and fluoroquinolone-selected mutants were examined. Overall, 23.5% and 71.8% of the isolates tested were susceptible to ciprofloxacin and levofloxacin, respectively. The MPC50 of ciprofloxacin was 128 mg/L, and the MPC50 of levofloxacin was 51.2 mg/L. The MPC50/MIC50 ratio for ciprofloxacin was 64, whereas that for levofloxacin was 25.6. The coefficient of determination between the MPC and MIC for ciprofloxacin and levofloxacin was 0.72 and 0.56, respectively, in the linear regression analysis. Preexisting mutations in GyrA (S83I, S83R, and D87Y) were identified in 18 clinical isolates, all of which were resistant to both ciprofloxacin and levofloxacin. Additional amino acid substitutions in GyrA were identified in all ciprofloxacin- and levofloxacin-selected mutants. Furthermore, GyrB alterations (D431N or D431H) were found in nine levofloxacin-treated isolates. Given that maintaining the serum concentrations of fluoroquinolones above MPCs is impossible under presently recommended doses, the selection of mutant E. anophelis strains seems inevitable.