A strip-based assay for detection of CrfA enzyme activity to differentiate Mycobacterium tuberculosis and non-tuberculous mycobacteria.

There is an unmet need for tools that permit diagnosis of Tuberculosis (TB) that are affordable, low-tech, and can differentiate Mycobacterium tuberculosis (M.tb) from non-tuberculous mycobacteria (NTM). In this study, we have developed a strip-based assay to detect the activity of a unique Carbapenem Resistance Factor A (CrfA) enzyme present only in M.tb. The strip comprises of PVDF (Polyvinylidene fluoride) membrane that has an immobilized anti-CrfA antibody to capture the CrfA enzyme from M.tb lysate. Lysate of mycobacteria is applied to the strip, washed, and incubated in the presence of chromogenic reporter dye which is a substrate for CrfA. A change in the color of the dye that is readily visible to the naked eye is the readout. We evaluated lysates from M.tb and various NTMs namely, M. abscessus, M. chelonae, M. avium, M. obuense, M. paraintracellulare, M. kansasi, including the patient-derived sputum samples. The strip assay selectively identified only those samples containing M.tb. Based on this evidence, this new assay enables the identification and differentiation of M.tb from NTMs in patient sputum samples. As this tool can be simple to use, therefore has the potential to serve the unmet need for diagnosis of TB and NTM infections in resource-limited settings.