colistin, an option for treatment of multiple drug resistant pseudomonas aeruginosa

introduction: multi-drug resistant (mdr) p. aeruginosa is constantly increasing and causing severe issues in combatting widely spread health problems. the aim of this study was to assess colistin susceptibility in mdr p. aeruginosa isolates obtained from different infection sites. methods: ninety clinical isolates of p. aeruginosa were collected from different hospitals of the tabriz university of medical sciences. all isolates were identified using standard microbiology tests. the disk diffusion susceptibility testing was performed according to the clinical and laboratory standards institute (clsi) guidelines. antibiotic disks used in this study included ciprofloxacin, levofloxacin, ceftazidime, amikacin, gentamicin, cefepime, imipenem, meropenem, ticarcillin/clavulanic acid, piperacillin, aztreonam, and colistin. the mic (minimum inhibitory concentration) of colistin was determined by the agar dilution method according to clsi guidelines. results: mdr isolates were found in 75.6%, in which there was a high frequency in wound specimens (23.3%), followed by blood (17.8%), urine (15.6%), trachea (13.3%), and peritoneum (5.6%). high resistance rate (above 50%) was observed with piperacillin, aztreonam, ceftazidime, cefepime, meropenem, gentamicin, amikacin, ciprofloxacin, and levofloxacin. all isolates were found to be susceptible to colistin through the disk diffusion method; however, two isolates were non-susceptible in the agar dilution method. conclusion: the present study shows a high frequency of mdr p. aeruginosa in our subjects, the limitations of empirical therapy, and the need for susceptibility testing. the most effective antibiotic against mdr p. aeruginosa was colistin. therefore, colistin may be an alternative antimicrobial agent for infections due to mdr p. aeruginosa.