GyrA mutations in ciprofloxacin-resistant clinical isolates of Pseudomonas aeruginosa in a Silesian Hospital in Poland.

Among 73 clinical isolates of Pseudomonas aeruginosa 48 strains were ciprofloxacine (CIP) susceptible and 25 CIP resistant (Minimal inhibitory concentration--MIC>32 microg/ml - 14 strains) or of intermediate susceptibility to CIP (MIC > or = 1,5 - 32 microg/ml - 11 isolates). Mutations in the quinolone-resistance-determining region (QRDR) of gyrA gene were searched in groups of CIP resistant and of intermediate susceptibility to CIP isolates. Two methods: restriction fragment length polymorphism (RFLP) analysis and DNA sequencing analysis allowed to detect three different mutations. The nucleotide substitutions observed led to the following amino acid replacements: Thr-83 --> Ile, Asp-87 --> Asn, Asp-87 --> Gly. One mutated strain among the group of mutants analyzed showed double mutation (Thr-83 --> Ile, Asp-87 --> Gly) and additional silent mutation (Val-103 --> Val); whilst the rest of the isolates showed different single missense mutations. The most frequently detected mutation in the gyrA gene (16 out of 25 mutants) was the Thr-83 --> Ile substitution.