Background and purpose: Pseudomonas aeruginosa is an opportunistic pathogen in patients with chronic respiratory disease or in immunocompromised hosts. This bacterium shows intrinsic and acquired resistance to diverse antimicrobial agents. An important mechanism of resistance to fluoroquinolones in P. aeruginosa is the mutation in gyrA, a subunit of topoisomerases II. The aim of this study was to investigate the gyrA mutations in ciprofloxacin resistant isolates in Guilan province.

Materials and methods: In this cross-sectional study, 44 P. aeruginosa strains were isolated from different clinical samples such as burn, urine and respiratory secretions identified by biochemical tests. The antibiotic resistance and susceptibility of strains was determined by Kirby Bauer method. Chi-square test was carried out and P value of < 0.05 was considered statistically significant. PCR-sequencing was carried out to assess the gyrA mutations in drug resistant isolates. CLC main workbench v3.5 and BLAST softwares was used to compare gyrA sequence in resistant isolates with reference gene in PAO1.

Results: The highest MIC of ciprofloxacin in some strains was >512 μg/ml. T83I and D87Y mutations were determined in gyrA gene in resistance isolates. Also, this study showed no relationship between MIC of ciprofloxacin in resistant isolates and mutation in gyrA.

Conclusion: These results demonstrated that gyrA mutations are one of the most important mechanisms of resistance to ciprofloxacin in clinical strains of P. aeruginosa in Guilan. It is believed that mutations in gyrA alongside several genes that are involved in development of resistance have increased the resistance in different strains.