Distribution and Molecular Characterization of Resistance Gene Cassettes Containing Class 1 Integrons in Multi-Drug Resistant (MDR) Clinical Isolates of Pseudomonas aeruginosa

Purpose: The integrons, as the mobile exogenous elements, play a prominent role in the spreading of antimicrobial resistance genes from Pseudomonas aeruginosa clinical isolates to other bacteria. This study aimed to investigate the frequency of class 1 integrons andresistance gene cassettes carrying by them in clinical isolates as well as multidrug resistant P. aeruginosa. Materials and Methods: A total of 100 clinical isolates of P. aeruginosa were collected from 5 hospitals in Mazandaran province, north Iran. The antibiotic susceptibility pattern of the isolates was evaluated using the disk agar diffusion method. Genomic DNAs were extracted and then the presence of class 1 integrons was detected by the PCR test. All PCR products of the positive isolates were sequenced for the detection of resistance gene cassettes by the Sanger method. Results: Forty-one percent of the clinical isolates were multi-drug resistant. Also, 42% of the isolates were contained class 1 integron, and 61.9% of the integron positive isolates were detected as MDR. We detected 10 different gene cassettes sizing from 0.6 to 3.5 kb in the present study. The sequencing analysis of the internal variable regions of the class 1 integrons showed that the 0.75 kb gene cassette (aadB) was the most frequent resistance gene (54.76%) among all clinical isolates, as well as the MDR isolates. Other resistance genes detected in this study were included: aadA6-orfD (35.71%), aacA4-bla(OXA- 1)0 (21.42%), aadB-aacA4-bla(OXA- 10) (19.04%), bla(OXA-10)-aacA4-VIM1 (11.9%), aacA4-cat B10 (7.14%), aacA5-aadA1-cmlA5 (7.14%), bla(OXA31)-aadA2 (4.76%), and aac(3)-Ic-aac A5-cmlA5 (4.76%). To the best of our knowledge, bla(OXA-10)-aacA4-VIM1 cassette array is detected for the first time in this study. Conclusion: The treatment of infections caused by P. aeruginosa in this region of Iran is a major problem due to the high prevalence of class 1 integrons. It seems that the high prescription of beta-lactams and aminoglycosides for the treatment of these infections may be replaced by other combination therapy stewardships.