Prevalence of class 1 and 2 integrons among the multidrug resistant uropathogenic strains of Escherichia coli

Background: Multidrug resistance is a serious problem in the treatment of urinary tract infections. Horizontal gene transfer, directed by strong selective pressure of antibiotics, has resulted in the widespread distribution of multiple antibiotic resistance genes. The dissemination of resistance genes is enhanced when they are trapped in integrons. Objectives: To determine the prevalence of integrons among multidrug resistant Escherichia coli strains collected from regional hospitals and private clinical laboratories in Alborz province. Methods: The susceptibility of 111 clinical Escherichia coli isolates was tested using a Kirby-Bauer disk diffusion method for common antibiotics. Isolates were screened for the production of extended spectrum beta-lactamases (ESBLs) using a double disk synergy test. The existence of integrons was confirmed by amplification of the integrase gene and their class determined via analysis of PCR products by PCR-RFLP. Results: Isolates showed the highest resistance to amoxicillin. Nitrofurantoin, amikacin, and ceftizoxime were the most effective antibiotics in vitro. Eighty-eight isolates of 111 (79%) were resistant to more than three unrelated drugs. We found 30% of the multidrug resistant isolates harbor integrons. Class 1 and 2 integrons were detected in 25 and 1 isolates, respectively. ESBL screening of strains showed 45 isolates (40%) were positive; 22% of the ESBL-positive isolates carried class 1 integrons and the frequency of MDR in ESBL-positive isolates was 93%. Conclusion: The existence of integrons in only 29.5% of multidrug resistant isolates showed that besides integrons, antibiotic resistance genes were probably carried on other transferable elements lacking integrons, such as transposons or plasmids.