A new approach for pyrazinamide susceptibility testing in Mycobacterium tuberculosis

Abstract

Background: Pyrazinamide (PZA) is an important drug in the treatment of tuberculosis. Microbiological methods of PZA susceptibility testing are controversial and have low reproducibility. After conversion of PZA into pyrazinoic acid (POA) by the bacterial pyrazinamidase enzyme, the drug is expelled from the bacteria by an efflux pump.

Objective: To evaluate the rate of POA extrusion from Mycobacterium tuberculosis as a parameter to detect PZA resistance.

Methods: The rate of POA extrusion and PZA susceptibility determined by BACTEC 460 were measured for 34 strains in a previous study. PZA resistance was modeled in a logistic regression with the pyrazinoic efflux rate.

Result: POA efflux rate predicted PZA resistance with 70.83%-92.85% sensitivity and 100% specificity compared with BACTEC 460.

Conclusion: POA efflux rate could be a useful tool for predicting PZA resistance in M. tuberculosis. Further exploration of this approach may lead to the development of new tools for diagnosing PZA resistance, which may be of public health importance.

FIG. 1.

Correlation between the pyrazinoic acid (POA) efflux rate estimated from a 48-hr culture, V_POA(48h) (0, 12, 24, 36, and 48 hr), and estimated from a 12-hr culture, V_POA(12h) (0, 12 hr).

FIG. 2.

Sensitivity and specificity that determine pyrazinamide resistance based on the POA efflux rate for different cutoffs of the predicted probability. (A) Prediction of Bactec resistance (% growth >11%) based on V_POA(12h); (B) prediction of Bactec resistance (% growth >11%) based on V_POA(48h); (C) prediction of Bactec resistance (% growth >20%) based on V_POA(12h); (D) prediction of Bactec resistance (% growth >20%) based on V_POA(48h).