Zahra Aghapour - Drug applied research center, Tabriz University of Medical Sciences,Tabriz, I.R. Iran
Pourya Gholizadeh - Student Research Committee, Tabriz University of Medical Sciences, Tabriz, I.R. Iran
Hossein Samadi Kafil - Drug applied research center, Tabriz University of Medical Sciences,Tabriz, I.R. Iran

Background and Aim:Colistin is a last line antibiotic for treating severe infections caused by multidrug-resistant Gram-negative bacteria. Unfortunately, the increased use of this agent has led to the emergence of colistin-resistant bacteria. The aim of this study was to determine colistin resistance in clinical Gram-negative isolates.Methods:Nine-hundred clinical isolates were collected from hospitalized patients in Imam-Reza and Pediatric, teaching and treatment hospitals, Tabriz, Iran, during the period from 2014 to 2016. The Gram-negative bacteria belong to Enterobacteriaceae such as Escherichia coli, Klebsiella spp., Acinetobacter baumannii, Enterobacter agglomerans and Pseudomonas aeruginosa were selected. Antibiotic susceptibility of the isolates was determined by disk diffusion and agar dilution methods.Results:Of the 900 clinical isolates, 30 (3.33%) were identified as a colistin resistance and 26.6% of them were highly resistant. Colistin resistant of E.coli were 43.3%, Klebsiella spp.13.3%, A. baumannii, E. agglomeranse, and P. aeruginosa were 13.3%, 10%, 13.3%, respectively.Conclusion:The frequency of resistance to colistin was low in the Northwest of Iran. In the battle against rapidly emerging bacterial resistance we can no longer rely entirely on the discovery of new antibiotics; we must also pursue rational approaches to the use of older antibiotics such as colistin.

Colistin-resistant, Gram negative bacteria, Agar dilution, Disk diffusion