A continuously monitored colorimetric method for detection of Mycobacterium tuberculosis complex in sputum
OBJECTIVE: To develop a new liquid culture method to detect Mycobacterium tuberculosis complex (MTC) in sputum using 2,3-diphenyl-5-thienyl-(2)-tetrazolium (STC), the nitrate reductase assay (NRA) and p-nitrobenzoic acid (PNB).
DESIGN: Ninety-three sputum samples collected from 18 tuberculosis patients were decontaminated with N-acetyl-L-cysteine-sodium hydroxide using MGIT™ 960 and in STC-NRA cultures, both in the presence and in the absence of PNB, an inhibitor of MTC growth. The reduction of STC by colour change indicated mycobacterial growth; NRA was then performed to confirm MTC.
RESULTS: STC-NRA culture was positive for acid-fast bacilli in 66/93 (71%) samples, of which 60/93 (64.5%) were identified as MTC-positive and 6/93 (6.5%) as indeterminate mycobacteria. MGIT indicated MTC in 59/93 (63.4%) cultures. Contamination was detected in 12/93 (13%) STC-NRA cultures vs. 29/93 (31.2%) MGIT cultures. The mean time to detection (TTD) of MTC using STC-NRA was 14 days and 7 days using MGIT.
CONCLUSION: The STC-NRA method is sensitive for the detection of MTC in sputum. TTD increased with duration of anti-tuberculosis treatment, highlighting the value of this method in monitoring treatment success. The method is simple and inexpensive and, unlike MGIT, does not require technical equipment. The preliminary performance characteristics of the method should be further evaluated in larger studies.
Keywords: 2,3-diphenyl-5-thienyl-(2)-tetrazolium STC; TTD; liquid culture; nitrate reductase assay; treatment monitoring
Document Type: Research Article
Affiliations: 1: National Institute of Medical Research, Mbeya Medical Research Center, Mbeya, Tanzania 2: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich, Munich, Germany; German Centre for Infection Research, Munich, Germany 3: Laboratorio de Microbiología Clínica, Instituto de Medicina Tropical Alexander von Humboldt, Universidad Peruana Cayetano Heredia, Lima, Peru 4: National Institute of Medical Research, Mbeya Medical Research Center, Mbeya, Tanzania; Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich, Munich, Germany 5: Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich, Munich, Germany 6: National Institute of Medical Research, Mbeya Medical Research Center, Mbeya, Tanzania; Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich, Munich, Germany; German Centre for Infection Research, Munich, Germany
Publication date: 01 December 2013
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