Rapid Identification and Drug Susceptibility Testing of Mycobacterium tuberculosis: Standard Operating Procedure for Non-Commercial Assays: Part 3: Colorimetric Redox Indicator Assay v1.3.12

The previous two standard operating procedures (SOPs) related to the culture and drug susceptibility testing (DST) of Mycobacterium tuberculosis with the microscopic observation drug susceptibility assay (Part 1) and nitrate reductase assay (Part 2). The present SOP is devoted to a third non-commercial culture and DST method known as colorimetric redox indicator assay (CRI). As its name indicates, the CRI detects the ability of the M. tuberculosis to reduce the colored oxidation-reduction indicator when added to a liquid culture of M. tuberculosis, after exposing the growth to different anti-mycobacterial drugs. The change in the color of the indicator denotes the proportionate number of viable Mycobacteria in the medium. The identification and DST results can be obtained in 7-8 days. This SOP document has been developed through the culture and DST subgroup of the STOP tuberculosis (TB) Partnership New Diagnostic Working Group. It is intended for laboratories that would want to use or already use this rapid non-commercial method for culture identification and DST of M. tuberculosis, notably in resource-constraint settings in Asia and Africa.