Correlation between resistance of Pseudomonas aeruginosa to benzalkonium chloride and expression of efflux pump genes

Study of cross-resistance to other antimicrobial agents and efflux pump (EP) resistance mechanism in benzalkonium chloride (BC) adapted Pseudomonas aeruginosa isolates. Minimum inhibitory concentration (MIC) of BC of 88 P. aeruginosa isolates that collected from clinical settings in Egypt and cross-resistance of BC-adapted isolates to other antimicrobial agents were determined by agar dilution method. EP regulatory genes (i.e., MexR, NfxB, MexT, and MexZ) were detected by PCR in BC adapted isolates, and then EP activity of isolates which have these four genes was determined by cartwheel method followed by sequencing for the isolate which showed the highest EP activity. Finally; the expression of EP genes (MexA, MexC, MexE, and MexX) was determined in the same isolate by realtime polymerase chain reaction (RT-PCR) in presence and absence of the most potent efflux pump inhibitor (EPI). Twenty isolates were BC-adapted with MIC 2,048 mg/l, showed cross-resistance to cetrimide and ciprofloxacin but not to other disinfectants used. The isolate no. 87 selected to be sequenced. Mutation founded in MexR (V126E) and MexZ (L138R) genes. By RT-PCR, sertraline (the most potent EPI used) decreased the expression of the EP genes to three-folds. These results demonstrate that EP was the major mechanism of resistance to BC.