Iranian Journal of Medical Microbiology

Backgrounds: Uropathogenic Escherichia coli strains are the predominant causative organisms of urinary tract infections (UTIs). Aminoglycosides are clinically useful antibiotics with bactericidal activity against this bacterium. The most common mechanism for resistance to these antibiotics are mediated through production of aminoglycoside modifying enzymes (AMEs). The most common of these enzymes are Aminoglycoside Acetyltransferases (AACs). The epidemiology of the dominant type of these enzymes, AAC(3)-II, varies from region to region. The aim of this study was to determine the antimicrobial susceptibility pattern with a focus on aminoglycosides and the prevalence of aac(3)-IIa gene among clinical isolates of uropathogenic Escherichia coli obtained from Delfan, Lorestan, Iran.

Materials and Methods: In this descriptive study, a total of 100 uropathogenic Escherichia coli isolates were collected from BoAli hospital in Delfan city, Lorestan, from July to November 2010. Antibiotic susceptibility patterns of the isolates were determined using disk diffusion method according to Clinical and Laboratory Standards Institute )CLSI) guidelines. Prevalence of aac(3)-IIa gene was determined by PCR and the relationship between resistance phenotypes to aminoglycosides and presence of aac(3)-IIa gene was evaluated.

Results: Among the 100 tested isolates, maximal resistance was seen to ampicillin (85%) whereas, no resistance to imipenem was found. Sixty percent of the isolates demonstrated resistance to at least one of the tested aminoglycosides. Resistance rate towards these agents were as followed: gentamicin 39%, kanamycin 26%, neomycin 31% and amikacin 1%. Forty–four isolates (44%) harbored the aac(3)-IIa gene. The maximal rate of gene presence (36 isolates, 92.3%) was detected in strains with gentamicin resistant phenotype (39 isolates, 39%).

Conclusion: On the basis of our findings, use of antibiotics such as nitrofurantoin, amikacin or imipenem are recommended for empirical treatment of UTIs. In addition, locally widespread distribution of aac(3)-IIa gene will pose concerns about progressive resistance against potent aminoglycosides such as gentamicin, tobramycin and others in  the future.