A comparison of the E-test and proportion methods for susceptibility testing of Mycobacterium tuberculosis

The aim of this study was to investigate the correlation between three anti biotic susceptibility methods, the proportion method on Lowenstein Jensen m edium (LJ medium), the proportion method on Middlebrook 7H11 agar (7H11 aga r), and the E-test for Mycobacterium tuberculosis. Fifty M, tuberculosis isolates were tested in vitro against isoniazid, rifa mpicin, streptomycin, and ethambutol according to the E-test, the proportio n methods on 7H11 agar and LJ medium and then compared with a reference tes t which was the proportion method on 7H11 agar, The correlations between pr oportion method on 7H11 agar and proportion method on LJ medium for isoniaz id, rifampicin, streptomycin, and ethambutol were 93.9%, 85.1%, 85.4% and 7 8.7% respectively. The correlations between the proportion method on 7H11 a gar and the E-test were 83.1%, 78.8%, 84.7% and 80.5% respectively. There w ere no significant differences observed between the E-test and LJ medium co mpared to 7H11 agar, The average times to obtain susceptibility test result s were 7 and 21 days for the E-test and agar proportion methods, respective ly. The E-test may be suitable for replacing the proportion methods (7H11 a gar and LJ medium) in routine practice due to its fast and easy application .