High Frequency of Integron-Associated Cassette Arrays Containing dfrA and aad Genes in Urinary Isolates of Escherichia coli in the Southwest of Iran

The emergence of multidrug (MDR) isolates of Escherichia coli has made the treatment of urinary tract infections (UTI) very challenging. Integrons are considered to be one of the most important mechanisms in the dissemination of resistance genes. In the current study, we sought to investigate the antibiotic resistance patterns, class 1-3 integrons and corresponding gene cassettes in urinary isolates of E. coli in the southwest of Iran. A total of 144 E. coli isolates were collected from the patients with UTIs. Antibiotic susceptibility test conducted by the disc diffusion method using 12 different antibiotics. The polymerase chain reaction (PCR) was used for the detection of intl1, intI2, and intI3 genes. To analyze the gene cassettes, variable regions of class 1 integron were amplified by PCR and subjected to sequencing. The highest rates of resistance were exhibited to amoxicillin/clavulanic (73.6%), trimethoprim-sulfamethoxazole (63.9%) and tetracycline (63.2%). Totally, intI1 and intI2 genes were identified in 62.5 and 9% of isolates. One-hundred and nine (75.7%) E. coli isolates were multidrug resistance (MDR), among which 78% harbored intI1 gene. Also, all of the intI2 positive E. coli isolates were MDR. Ten different gene cassette arrays were found in intl1 positive E. coli including dfrA5, dfrA25, dfrA7, aacA4, aadA1, aadB-catB3, dfrA17-aadA5, dfrA12-orfF-aadA2, aadA1-bla(OXA-30), and dfrA5-catB3-aacA4. The dfrA17-aadA5 was the most prominent gene cassette array among E. coli isolates. Characterization of resistance gene cassettes located in integrons in this study showed a high frequency of dfrA and aad genes which confer resistance to trimethoprim and aminoglycosides. The obtained result from this study could be useful in planning to prevent the rising rate of antibiotic resistance.