Role of Efflux Transporters in Resistance of Pseudomonas aeruginosa to Fluoroquinolones

Proton gradient – dependent efflux pumps play important role in multidrug resistance (MDR) in Pseudomonas aeruginosa. 23 MDR strains were selected from 104 clinical isolates of P. aeruginosa and screened for resistance to ceftazidim, ceftriaxone, ciprofloxacin, ofloxacin, amikacin, gentamicin and ethidium bromide by determining MICs. The MICs of EtBr and antibiotics were also measured in presence of protonophore, carbonyl cyanide m-chlorophenyl hydrazone (CCCP). Active efflux was assessed using ethidium bromide accumulation assays. Drug accumulation studies for fluoroquinolones were performed to determine the drug specificity of efflux. PCR was used to identify the mexAB-oprM gene in clinical isolates of P. aeruginosa. CCCP reduced the MICs of antibiotics at least in 1 dilution. Ethidium bromide accumulation assays confirmed the presence of proton gradient – dependent efflux mechanism in clinical isolates of P. aeruginosa and accumulation assays of fluoroquinolones showed that efflux systems in this bacterium extrude the structurally and functionally dissimilar antimicrobial agents. PCR demonstrated that 17% of clinical isolates of P. aeruginosa had the mexAB-oprM genes on the chromosome. This study indicates the presence of other RND efflux pumps, in addition to MexAB-OprM in multidrug resistance in clinical isolates of P. aeruginosa.