Distribution of Integrons and Gene Cassettes among Metallo-β-Lactamase Producing Pseudomonas aeruginosa Clinical Isolates

Integrons are considered as to play a significant role in the evolution and spread of antimicrobial resistance genes.
A total of 120 clinical isolates of Pseudomonas aeruginosa (collected from Zanjan hospitals between March 2015 and February 2016) were investigated for molecular characterization of MBLs and Class I and II integrons. Antimicrobial susceptibility testing was also performed based on the CLSI guidelines. The frequency of MBL producing isolates and the susceptibility to various antimicrobial agents were investigated.
Based on the obtained results, BlaIMP was the most frequently detected metallo-β-lactamase. The frequency of blaVIM, blaSPM, and blaSIM, in MBL producing isolates was 17.1, 57.1, and 14.1%, respectively. No blaGIM harboring isolate was detected in our study. We detected two (5.7%) multidrug resistant P. aeruginosa strains isolated from the urine and sputum samples, which harbored blaNDM-1. These isolates also contained blaIMP and blaSPM. Class I integron was detected in 94.3% of the MBL positive isolates while 8.5% of the isolates contained Class II integrons. Of five different gene cassettes identified in Class I and II integrons, cassette encoding resistance to trimethoprim (dfr) was found to be predominant.
These results indicate that Class I integrons are widespread among the MBL producing P. aeruginosa isolates. Therefore, appropriate surveillance and control measures are essential to prevent the further spread of MBL and integron producing P. aeruginosa in hospitals.­­