New Mutations in Ciprofloxacin Resistant Strains of Pseudomonas aeruginosa Isolated from Guilan Province, Northern Iran

Abstract

Pseudomonas aeruginosa (P. aeruginosa) is a gram-negative bacterium that continues to be a major cause of opportunistic nosocomial infections. In P. aeruginosa, several fluoroquinolones resistance mechanisms have been proposed such as mutations in the target enzymes GyrA and ParC and upregulation of efflux pump MexAB-OprM. Fluoroquinolones inhibit the target enzymes DNA gyrase and topoisomerase IV, each comprised of two subunits: GyrA and GyrB, and ParC and ParE, respectively. In addition, fluoroquinolones were blocked by overexpression of MexAB-OprM induced through mutations in the regulatory genes mexR and nalC. In this study, 44 P. aeruginosa strains were isolated from different clinical samples of burn and infection from patients in some hospitals and laboratories in Guilan, which were identified by biochemical tests. The antibiotic resistance and susceptibility of strains was determined by Kirby Bauer method and microdilution method, and then PCR-sequencing was carried out to assess mutation in several genes involved in ciprofloxacin resistance. Of 44 isolates, 14 isolates were fluoroquinolone resistant. All 14 strains were nalidixic acid resistant with MIC = 1024 μg/mL. While ciprofloxacin resistance was showed in resistant isolates with MIC to be 32–1024 μg/mL. PCR-sequencing analysis showed that all 14 fluoroquinolone resistant isolates had one or two mutations in gyrA mutation. Mutations in parC, mexR and nalC were shown in some ciprofloxacin resistant isolates. Moreover, three strains had new mutation in mexR gene (111InsC and 262-263delAG). It seems that high resistance to ciprofloxacin can simultaneously be the result of mutation in several genes such as topoisomerase enzymes and negative regulatory genes implicated in the expression of efflux pump systems in Guilan Province.