Detection of Pyrazinamide Heteroresistance in Mycobacterium tuberculosis

Abstract

Heteroresistance is defined as the coexistence of both susceptible and resistant bacteria in a bacterial population. Previously published data show that it may occur in 9-57% of Mycobacterium tuberculosis isolates for various drugs. Pyrazinamide (PZA) is an important first-line drug used for treatment of both drug-susceptible and PZA-susceptible multidrug-resistant TB. Clinical PZA resistance is defined as a proportion of resistant bacteria in the isolate exceeding 10%, when the drug is no longer considered clinically effective. The capability of traditional drug susceptibility testing techniques to detect PZA heteroresistance has not yet been evaluated. The aim of this study was to compare the capacity of BACTEC MGIT 960, Wayne’s test and whole genome sequencing (WGS) to detect PZA resistant subpopulations in bacterial suspensions prepared with different proportions of mutant strains. Both BACTEC MGIT 960 and WGS were able to detect the critical level of 10% PZA heteroresistance whereas Wayne’s test failed to do so, with the latter falsely reporting highly resistant samples as PZA susceptible. Failure to detect drug resistant subpopulations may lead to inadvertently weak treatment regimens if ineffective drugs are included, with the risk of treatment failure with the selective growth of resistant subpopulations. We need clinical awareness of heteroresistance as well as evaluation of new diagnostic tools in their capacity in detecting heteroresistance in TB.

Exploring Diagnostic Methods for Drug-Resistant Tuberculosis: A Comprehensive Overview

“…However, applying less strict filters in WGS might cause more background noise and less specificity because sequencing artifacts or other contaminant bacteria could be reported as "true variants". The Wayne's test did not detect any HR [125]; these poor results are in contrast with a systematic review and meta-analysis, where Nasiri found that the sensitivity and specificity of the Wayne test were 86.6% and 96.0% [126].…”