Drug susceptibility testing in tuberculosis: a comparison of the proportion methods using Lowenstein-Jensen, Middlebrook 7H10 and 7H11 agar media and a radiometric method.

In the present investigation, the conventional drug susceptibility testing procedures using the 1% proportion method on Löwenstein-Jensen (LJ) and Middlebrook 7H10/7H11 agar media were compared with a recent radiometric method. The latter using "Bactec 460-TB" apparatus and a special broth medium (Becton and Dickinson Diagnostic Instrument Systems, Towson, MD, USA) gave drug susceptibility results within a week as compared to 4-5 weeks with the LJ method, and 3-4 weeks using 7H10/7H11 agar media. This report describes the critical concentrations retained for each of the methods and the methodology used. Also, the compatibility of the results obtained with the radiometric method with those obtained with conventional 7H11 agar method was perfect. In this report, we justify the choice of the 7H11 agar method instead of the LJ method as our conventional drug susceptibility procedure, and suggest also that radiometric drug susceptibility determination by Bactec 460-TB apparatus may be the method of choice for routine, rapid drug susceptibility determinations.