A simple and economical in-house phage technique for the rapid detection of rifampin, isoniazid, ethambutol, streptomycin, and ciprofloxacin drug resistance in Mycobacterium tuberculosis, directly on decontaminated sputum samples.

Objectives: The early detection of drug resistance would be a boon for TB control programs. The aim of the present study was to set up a rapid phage assay for the testing of drug susceptibility of Mycobacterium tuberculosis to rifampin, isoniazid, ethambutol, streptomycin, and ciprofloxacin, directly on decontaminated sputum samples.
Methods: Mueller-Hinton broth was used instead of 7H9 broth to make the method more economical. Vancomycin and polymyxin B were added to the concentrated sputum samples to reduce the bacterial contamination. The phage assay on decontaminated sputum samples was compared with the proportion method using M. tuberculosis isolates from the same sputum samples.
Results: Phage assay results were available within 48h for rifampin and streptomycin and within 72h for all the other drugs. In contrast the proportion method required 4-6 weeks from the primary cultures. The sensitivity of the phage assay was in the range of 93% to 100% and specificity in the range of 96% to 100% for all the drugs tested. The interpretation of results was possible for 334 of the 370 (90.3%) acid-fast bacillus (AFB) smear-positive sputum samples by the phage assay.
Conclusions: The phage assay for the detection of drug resistance on direct decontaminated sputum samples is economical, easy to perform, and rapid.
(Copyright © 2012 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.)