Rapid drug susceptibility testing of mycobacteria in tissue culture medium

Mycobacteria grew rapidly in FST medium (tissue culture medium F12 supplemented with 5% serum and 0.05% Tween 80). Growth of Mycobacterium tuberculosis and other niacin-negative mycobacteria in flat-bottomed, 96-well tissue culture plates was estimable by the naked eye within 3 to 5 days when mycobacteria were inoculated at 0.1 to 0.01 Klett units (5 X 10(4) to 0.5 X 10(4) CFU) per well. Spontaneous resistant variants of M. tuberculosis to isoniazid arose and grew in the medium within 2 weeks of culture. A total of 56 clinically isolated mycobacteria whose drug susceptibilities had been tested by a conventional method were tested in FST medium for minimal inhibitory concentrations of streptomycin, ethambutol, rifampin, and isoniazid. The minimal inhibitory concentrations of these drugs in FST medium strictly coincided with the drug susceptibility patterns obtained by a conventional method, except for 3 of 224 estimations.