MODS-Wayne: A colorimetric adaptation of the MODS assay for the detection of Mycobacterium tuberculosis pyrazinamide resistance from sputum samples.

14 Nov 2018
Alcántara R, Fuentes P, Antiparra R, Santos M, Gilman RH, Kirwan DE, Zimic M, Sheen P,

Although pyrazinamide (PZA) is a key component of first and second line tuberculosis treatment regimens, there is no gold standard to determine PZA resistance. Approximately 50% of multidrug-resistant tuberculosis (MDR-TB) and over 90% of extensively drug resistant tuberculosis (XDR-TB) strains are also PZA resistant. pncA sequencing is the endorsed test to evaluate PZA susceptibility. However, molecular methods have limitations for their wide application.In this study we standardized and evaluated a new method to determine PZA resistance: MODS-Wayne. MODS-Wayne is based on the detection of pyrazinoic acid, the hydrolysis product of PZA, directly in the supernatant of sputum cultures by detecting a color change following addition of 10% ferrous ammonium sulfate. Using a PZA concentration of 800 µg/mL, sensitivity and specificity were evaluated at three time different periods of incubation (Reading 1, reading 2, reading 3)) using a composite standard (MGIT-PZA, pncA sequencing, and the classic Wayne test).MODS-Wayne was able to detect PZA resistance with a sensitivity and specificity of 92.7% and 99.3% respectively at Reading 3. MODS-Wayne had an agreement of 93.8% and a kappa index of 0.79 compared to the classic Wayne test, agreement of 95.3% and kappa index of 0.86 compared to MGIT-PZA, and agreement of 96.9% and kappa index of 0.90 compared to pncA sequencing. In conclusion, MODS-Wayne is a simple, fast, accurate, and inexpensive approach to detect PZA resistance, making this an attractive assay especially for low resource countries, where TB is a major public health problem.