Some aspects of determination of the sensitivity of Mycobacterium tuberculosis to ethambutol using a semiliquid medium

In addition to the earlier developed rapid technique for determining the drug resistance of Mycobacterium tuberculosis (MBT) to essential antituberculous drugs by using semiliquid medium (SLM), the author proposes a procedure for determining their resistance to ethambutol. She shows it necessary to use the drug only as a powder. The mean minimum suppressing concentrations of ethambutol in the semiliquid medium have been determined for stock cultures, sensitive and resistant strains, which are 3.5 +/- 2.5, 4.5 +/- 1.4, 8.5 +/- 1.6 micrograms/ml. Parallel determination of the sensitivity of 91 MBT strains by using the standard Lowenstein-Jensen medium and SLM has yielded the optimum concentration of ethambutol (5 micrograms/ml), which is marked by the highest (84.4%) percent of coincidence of results.