Evaluation of Antimicrobial Resistance Among Gram-Negative Isolates Collected from Intensive Care Units and Reliability of Routine Disc Susceptibility Tests at a Teaching Hospital in Tehran

Antibiotic resistance of intensive care unit (icu) born aerobic gram-negativebacteria was evaluated during a six months period at a teaching hospital in tehran, anddetermination of the validity of the results obtained from disc diffusion tests, using discsmanufactured in iran.disc susceptibility tests using iranian and standard discs (diffusion discs available ininternational markets) were performed on 108 aerobic gram-negative isolates obtained fromthe clinical samples of patients with at least 72 hours of stay in the icu. the minimuminhibitory concentrations (mic) was subsequently determined by collaborators not involvedwith the disc testing evaluation.acinetobacter was the most frequently isolated gram negative species (26%). highresistance rates were obtained for all antibiotics studied except for imipenem (98% sensitive).results of disc diffusion tests performed by the iranian discs were in moderate to strongagreement with those obtained from the standard discs . when comparing disc results withthe mic results, it was noted that the total number of very major, and minor discrepancieswere approximately the same with both sets of discs. the total number of major discrepancieswas higher for the iranian discs (more false positive results) . the total number of very majordiscrepancy rates was more than the acceptable 1.5% limits for each antibiotic tested, usingboth iranian and standard discs .high rates of resistance in aerobic gram-negative isolates studied, leaves imipenem as theonly reliable agent for the empirical treatment of icu infections. the high rates of very majordiscrepancies with both sets of discs show that physicians cannot rely on disc diffusion testsonly, in order to guide therapy for the treatment of very serious infections in the icus, even ifstandard discs are used instead of the iranian discs , and there is great need to establish a fastand easy way to determine the mic values . although it is better to repeat the study with a muchlarger sample size in order to make good judgment.