Comparison of nitrate reductase and automatic BACTEC MGIT 960 AST techniques for determining the drug sensitivity of mycobacteria tuberculosis

: The accelerated nitrate reductase method (NRM) developed at the Central Research Institute of Tuberculosis versus the automatic assay of drug sensitivity by means of a BACTEC 960 bacteriological analyzer was assessed. NRM was carried out, by using the Lowenstein-Jensen medium for 10 days. It is based on the detection of alive Mycobacteria tuberculosis, by recording their enzymatic activity. The study showed a good agreement of the results obtained by NRM with those obtained on a BACTEC 960 analyzer. Agreements were found for 52 isolates in 47 (90.4%) cases, the results disagreed in the testing of 5 (9.6%) cultures. The results of NRM were identical to those for 21 of the 22 cultures sensitive on a BACTEC 960 device; the coincidence was 95.5%. The sensitivity of NRM ranged from 88.2% (for rifampicin) to 96.3% (for isoniazid) and the specificity did from 96% (for isoniazid) to 100% (for streptomycin, rifampicin, and ethambutol). The positive prognostic value of NRM was 100% (for streptomycin, rifampicin, and ethambutol) and 96.3% (for isoniazid). The negative prognostic value of NRM ranged from 94.6 to 96.8% for individual drugs. The efficiency of NRM (a ratio of the number of correct results to the total number of results) was greater than 0.96, which suggests that this method and the BACTEC MGIT 960 AST technique may be regarded as rather comparable. The testing of NRM versus the automatic BACTEC MGIT 960 AST technique has indicated that the former may be successfully used to determine the sensitivity of Mycobacteria to the critical concentrations of first-line antituberculous agents.