Impact of nontuberculous mycobacteria on the performance of Xpert MTB/RIF and Xpert MTB/RIF Ultra for the detection of tuberculosis and rifampin resistance: a diagnostic accuracy study
10.5145/ACM.2025.28.4.2
- Author:
Sangsoo JUNG
;
Eunsang SUH
;
Jun-Ki LEE
;
Byung Woo JHUN
;
Tae Yeul KIM
;
Hee Jae HUH
;
Nam Yong LEE
- Publication Type:Original article
- From:Annals of Clinical Microbiology
2025;28(4):21-
- CountryRepublic of Korea
- Language:English
-
Abstract:
Background:The growing burden of nontuberculous mycobacteria (NTM) raises concerns regarding cross-reactivity in molecular tuberculosis (TB) diagnostics. In the current study, we evaluated whether high NTM loads affect Mycobacterium tuberculosis (MTB) detection or rifampin (RIF) resistance calls using Xpert MTB/RIF (Xpert) and Xpert MTB/RIF Ultra (Xpert Ultra).
Methods:In vitro spiking experiments were performed by mixing eight NTM species (1 × 10 6 colony-forming unit [CFU]/mL) with heat-inactivated MTB (RIF-susceptible H37Rv; RIFresistant S450L) at 5 × 103 CFU/mL in pooled smear-negative sputum, before testing them in parallel using Xpert and Xpert Ultra. We also retrospectively analyzed 334 results from lower respiratory specimens, including 32 NTM-positive specimens tested using both assays, and assessed the presence of probe amplification in the NTM-confirmed specimens.
Results:In spiking experiments, both assays showed no NTM-related cross-reactivity: RIFsusceptible mixes were “RIF resistance not detected,” S450L mixes were correctly resistant with preserved mutant melt peaks, and MTB-specific cycle threshold and melting peak temperature profiles were unchanged by NTM. Of the 334 clinical specimens, NTM was isolated from 32. Xpert classified all 32 as MTB-negative, and Xpert Ultra classified 31 of 32 as MTB-negative and one as “very low” positive in a patient with prior TB, consistent with residual nonviable DNA. In NTM-positive, Xpert/Xpert Ultra-negative specimens, neither assay showed probe amplification.
Conclusion:High-burden NTM did not compromise MTB detection or RIF-resistance determination using Xpert or Xpert Ultra. The assays demonstrated robust analytical specificity in mixed MTB–NTM contexts, supporting their use where NTM carriage is common.
