In order to evaluate the direct-method test of sensitivity to drugs
used in the principal tuberculosis treatment regimes, in the Organon
Teknika MB/BacT system, we tested 50 sputum samples positive to
microscopy taken from patients with pulmonary tuberculosis and with
clinical indications for an antibiogram, admitted sequentially for
examination during the routine of the reference laboratory. The
material was treated v/v with 23% trisodium phosphate solution,
incubated for 24 h at 35°C, and neutralized v/v with 20%
monosodium phosphate solution. The material was then centrifuged and
the sediment inoculated into flasks containing Rifampin - 2 μg/ml,
Isoniazid - 0.2 μg/ml, Pyrazinamide - 100 μg/ml, Ethambutol -
2.5 μg/ml, Ethionamide - 1.25 μg/ml, and Streptomycin - 2
μg/ml. The tests were evaluated using the indirect method in the
BACTEC 460 TB (Becton Dickinson) system as the gold standard. The
results showed that the Rifampin test performed best, i.e., 100%
sensitivity at 95% Confidence Interval (82.2-100) and 100% specificity
at 95% Confidence Interval (84.5-100), followed by Isoniazid and
Pyrazinamide. In this experiment, 92% of the materials showed a final
reading in 30 days; this period represents the time for primary
isolation as well as the results of the sensitivity profile, and is
within Centers for Disease Control and Prevention recommendations
regarding time for performance of the antibiogram. The inoculated
flasks showed no contamination during the experiment. The MB/BacT is
shown to be a reliable, rapid, fully automated nonradiometric system
for the tuberculosis antibiogram