Molecular mechanisms of fluoroquinolone resistance in Pseudomonas aeruginosa isolates from cystic fibrosis patients

Twenty P, aeruginosa isolates were collected from six cystic fibrosis (CF) patients, aged 27 to 33, in 1994 (9 isolates) and 1997 (11 isolates) at the CF Center, Copenhagen, Denmark, and were typed by pulse field gel electrop horesis (PFGE) or ribotyping, Five of the patients had isolates with the sa me PFGE or ribotyping patterns in 1997 as in 1994, and ciprofloxacin had a two- to fourfold higher MIC for the isolates collected in 1997 than those f rom 1994, Genomic DNA was amplified for gyrA, parC, mexR, and nfxB by PCR a nd sequenced. Eleven isolates had mutations in gyrA, seven isolates had mut ations at codon 83 (Thr to Ile), and four isolates had mutations at codon 8 7 (Asp to Asn or Tyr), Sixteen isolates had mutations in nfxB at codon 82 ( Arg to Leu). Increased amounts of OprN were found in six isolates and OprJ in eight isolates as determined by immunoblotting. No isolates had mutation s in parC or mexR. Six isolates had mutations in efflux pumps without gyrA mutations. The average number of mutations was higher in isolates from 1997 than in those from 1994. The results also suggested that efflux resistance mechanisms are more common in isolates from CF patients than in strains fr om urine and wounds from non-CF patients, in which mutations in gyrA and pa rC dominate (S, Jalal and B, Wretlind, Microb, Drug Resist, 4:257-261, 1998 ).