Laboratory Evaluation of Iranian Commercially Provided Antibiotic Disks With Conventional E-Test Method for Susceptibility Testing in Three Most Isolated Multi-drug Resistant Organisms

Abstract

Antimicrobial susceptibility testing is one of the most important tasks of clinical microbiology laboratories. This study was performed to compare accuracy of susceptibility testing carried out by disk diffusion method and E-test minimal inhibitory concentration (MIC) for detection antimicrobial resistance among three prevalent gram-negative organism isolated in an Iranian hospital . These organisms included Pseudomonas aeroginosa, Acenitobacter bumannii, and Klebsiella pneumoniaew which isolated from different Baquiatalah hospital wards .Disk diffusion method were carried out initially in Baqyatalah hospital microbiology laboratory. All isolates were sent to Iranian reference microbiology laboratory for detection of MIC by E-test method. Of 100 isolates, 52 isolates were Acinetobacter bumannii, 32 Pseudomonas aeroginosa and 16 Klebsiella pneumonia. All isolated strains were resistant to ciprofloxacin, imipenem, and amikacin by disk diffusion method. However there were significant differences compared with E-test method. Many strains were susceptible to above mentioned antibiotics by E-test method .Our study revealed that there was a controversy results between disk diffusion method and MIC determination technique by E-test. It may be due to lack of suitable internal quality control as well as poor quality of commercially provided disks in our country.