Analysis of correlation between resistance of carbapenem agents in Pseudomonas aeruginosa and mutation and altered expression of oprD2

Objective To investigate the impact on the resistance of carbapenem with the expression of OprD2 or OprD2 mutation in Pseudomonas aeruginosa. Methods One hundred and one clinical strains of Pseudomonas aeruginosa with MIC for imipenem ≥8 μg/ml were studied. MIC were determined by the broth microdilution method, and the antibiotics tested were imipenem(IPM ), biapenem( BPM), meropenem(MEM) and panipenem(PEM). The expression of the oprD2 gene in Pseudomonas aeruginosa were analyzed by real-time reverse transcriptase PCR(RT-PCR). For the Pseudomonas aeruginosa with normal expression of OprD2 and resistance to imipenem, full-length oprD2 gene was amplified by PCR and the products were sequenced. Results According to the result of the expression of oprD2 gene, 101 strains of Pseudomonas aeruginosa were divided into two groups: group1 with diminished expression of OprD2, and group2 with normal expression of OprD2. Comparing isolates with MIC of 4 kinds of carbepenem agents ≥ 16 μg/ml in two groups. Data showed the amount of OprD2 expression were different between two groups(P ＜0.01 or P ＜ 0.05). In group1, there are 28 isolates with MIC ≥ 16 μg/ml of all the 4 kinds of carbapenems, among which 25 isolates have obviously diminished expression of OprD2 ( ＜ 0.4). Negative correlations tendency appeared between the level of OprD2 transcription and MICs of 4 kinds of carbepenem agents in Pseudomonas aeruginosa. In group2, 16 strains with OprD2 mutation divided into 4 types according to the pattern of alteration. Compared with PAO1, these strains have increased MIC with different degree to IPM,BPM, MEM and PEM. Conclusion The deletion or diminished expression of OprD2 resulted in resistance to imipenem in Pseudomonas aeruginosa. The level of OprD2 transcription and antimicrobial activities for carbapenem agents proved to be highly correlated in Pseudomonas aeruginosa. The mutation of OprD2 in Pseudomonas aeruginosa probably decreased the sensitivity of carbapenem agents against Pseudomonas aeruginosa. Key words: Pseudomonas aeruginosa;  OprD porin protein;  Carbapenem resistance