Under the RNTCP, the method used for drug susceptibility testing is:

Propoion Method This is the method recommended for DOTS-Plus sites in India. It enables precise estimation of the propoion of mutants resistant to a given drug. Several 10-fold dilutions of inoculum are planted on to both control and drug -containing media; at least one dilution should yield isolated countable (50 -100) colonies. When these numbers are corrected by multiplying by the dilution of inoculum used, the total number of ble colonies observed on the control medium, and the number of mutant colonies resistant to the drug concentrations tested may be determined. The propoion of bacilli resistant to a given drug is then determined by expressing the resistant poion as a percentage of the total population tested. The propoion method is currently the method of choice. The economic variant of propoion method is used for DOTS-plus. Ref: