Colorimetric methods for detecting antimicrobial resistant mycobacteria: An overview

Phenotypic culture-based methods continue to be recommended for identification of the susceptibility profile to antimicrobials in mycobacterial isolates. For this, in-house colorimetric methods have been developed for detection of Mycobacterium tuberculosis and nontuberculous mycobacteria resistant strains, associated with an easier interpretation of results. Most existing colorimetric methods are based on the use of redox colorimetric indicators, such as resazurin and tetrazolium salts. Other tests require revealing solutions to generate color, while there are also tests that target the loss of color as a way of indicating bacterial growth. This review aimed to elucidate the available colorimetric methods to detect resistant mycobacterial strains, including their evaluation and application. Despite varying in terms of the format used, the methods presented in this review are relatively simple to perform and cheaper than molecular and semi-automated phenotypic methods, and can be implemented in different scenarios, including in limited resource settings.