Gene Cassette Array Analysis of Class 1 Integron among Pseudomonas aeruginosa strains isolated from Qom hospitals, Iran

Background: Pseudomonas aeruginosa is an important opportunistic nosocomial pathogen with multiple complex antibiotic resistance mechanisms. Integrons are versatile gene acquisition systems commonly found in bacterial genomes and widely known for their role in the horizontal dissemination of antibiotic resistance. Class 1 integron is widely distributed globally in a variety of bacterial species and sources and frequently harbors various antibiotic resistance genes. This study aimed to analyze gene cassettes in the variable region of class 1 integron among clinical isolates of Pseudomonas aeruginosa obtained from different wards of 5 hospitals in Qom, Iran. Data obtained from sequence analysis compared to result of antibiotic susceptibility test. Thus the proven role of the detected gene cassette was confirmed.Materials and Methods: 187 clinical Pseudomonas aeruginosa strains isolated from 5 hospitals in Qom, Iran from September 2012 to September 2013. Isolates confirmed by standard microbiological tests. Antibiotic susceptibility test performed on isolates for 6 antibiotics, tobramycin, gentamicin, ceftazidime, cefotaxime, cefepime and aztreonam by Kirby-Bauer method according to CLSI standard. Then presence of class 1 integron studied on all isolates by PCR method. intI1-positive strains entered another PCR assay designed to detect variable region of class 1 integron. Finally, PCR products analyzed for their nucleotide sequence. Results: Of 73 intI-positive isolates, 19 detected to contain intI1 variable region with different amplicon sizes, among which, 11 detected to contain blaOXA-10 and aac(6 )-II gene cassettes with an amplicon size of 1700bp. The cassette array blaOXA-10 - aac(6 )-II was detected. blaOXA-10 confers resistance to ceftazidime, cefotaxime, cefepime, aztreonam while aac(6 )-II confers resistance to tobramycin and gentamicin. Antibiotic susceptibility tests revealed that of 11 isolates, 10 (91%) were resistant to gentamicin. Also 9 (82%), 9 (82%), 10 (91%), 8 (73%) and 7 (64%) isolates were resistant to tobramycin, ceftazidime, cefotaxime, cefepime and aztreonam, respectively. The result confirms the role of these gene cassettes for modification of these aminoglycosides beta-lactam antibiotics by the produced enzymes.Conclusions: Considering the high prevalence of class 1 integrons containing gene cassettes for aminoglycoside modifying enzymes and beta-lactamases among resistant Pseudomonas aeruginosa isolates, it is necessary to adopt suitable strategies for infection control and treatment in Qom hospitals to prevent the spread of these resistance genes.

Keywords:

Pseudomonas aeruginosa , Integron , Gene Cassette