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 μg/ml - 14 strains) or of intermediate susceptibility to CIP (MIC≥ 1,5-32 μg/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.