Level of MexAB-OprM and OprD_2 expression in carbapenem-resistant Pseudomonas aeruginosa

Objective To investigate the expression level of efflux pump MexAB-OprM and porin protein OprD2 in P. aeruginosa and the relationship between their expression level and resistance to carbapenems. Methods A total of 655 clinical P. aeruginosa isolates were collected from 28 hospitals in 15 Chinese cities. Agar dilution technique was used to determine the MICs of imipenem and meropenem against P. aeruginosa before and after addition of efflux pump inhibitor CCCP. Real-time-RT-qPCR was used to test the expression level of MexAB-OprM and OprD2. SDS-PAGE and Western-blot were used to identify OprD2. Results The percentage of the collected P. aeruginosa isolates susceptible to imipenem and meropenem was 52.5% and 59.2% respectively. These figures did not change obviously after adding CCCP. MexAB-OprM was over-expressed in 52.0%(51/98) of the meropenem-resistant P. aeruginosa isolates (P0.05). The expression of OprD2 was lower in 43.7% (59/135) of the imipenem-resistant P. aeruginosa isolates (P0.05). And 14.8% (20/135) of the imipenem-resistant P. aeruginosa isolates had no OprD2 expression. SDS-PAGE and Western-blot confirmed this finding. Conclusions Both over-expression of MexAB-OprM and decreased or no expression of OprD2 are important mechanisms underlying the resistance of P. aeruginosa to meropenem and imipenem.