Efficacy of Disc Diffusion and Agar Dilution Methods in Evaluating Susceptibility to Antibiotics.

: In this study, efficacy and consistency of disc diffusion (DD) and agar dilution (AD) methods in determining susceptibility to antibiotics were evaluated using Brucella blood agar (BBA) in both methods and tetrazolium egg yolk agar (TEYA) in AD. : Twenty isolates were tested for susceptibility to nine antibiotics; metronidazole (MTZ), clarithromycin (CLR), amoxicillin (AMX), tetracycline (TET), ofloxacin (OFX), levofloxacin (LVX), ciprofloxacin (CIP), furazolidone (FRZ), and rifampin (RIF). Antibiotics solutions were impregnated into blank paper disks on BBA in the DD method or added to BBA (ADB) or TEYA (ADT) media in the AD method. Suspensions of isolates were surface or spot inoculated on solid media. Plates were incubated in CO incubator at 37°C for 5-7 days. : The highest rate of susceptibility to MTZ (65%) was determined by DD method compared with AD method (ADB: 40%, ADT: 30%). Both methods showed similar CLR (85%) and AMX (100%) susceptibility rates. Susceptibility to remaining antibiotics, determined by DD and ADB/ADT media were in respective order as 95%, 75% / 75% for TET, 100%, 95% / 85% for FRZ, 85%, 85% / 75% for OFX, 90%, 95% / 85% for LVX, 90%, 85% / 85% for CIP, and 100%, 85% / 75% for RIF. : DD and AD methods showed consistency in determining 161 (89.4%) susceptibility and resistance and inconsistency in determining 19 (10.6%) susceptibility and resistance ( < 0.05). DD is recommended as a cheap and easy method with the efficacy and precision comparable to the AD method in determining susceptibility to antibiotics.