A rapid method for determination of susceptibility of Mycobacterium tuberculosis to isoniazid, using...

A rapid isoniazid (INH) susceptibility test was developed for Mycobacterium tuberculosis by using acridinium-ester (AE)-labeled DNA probe. The method was applied to two reference strains and 20 clinical isolates, then compared with the standard proportion method. By comparing the difference of log relative light units (RLUs) M. tuberculosis cultures incubating in the presence and absence of INH, INH susceptibility could be determined with the AE-DNA probe after three to five days of incubation. The difference of log RLUs of susceptible strains was statistically significantly lower than that for resistant strains after incubation for three to five days. The cutoff value was defined as "mean + one standard deviation" of the difference between log RLU(INH) and log RLU(no INH) on Day 5. By this criterion, agreement between the AE-DNA probe and the proportion concentration method was found in 19 of 20 susceptibility tests (95%). The AE-DNA probe test is rapid and non-isotopic, and may provide a useful alternative method for INH susceptibility testing for clinical isolates of M. tuberculosis.