Variable ability of rapid tests to detect Mycobacterium tuberculosis rpoB mutations conferring phenotypically occult rifampicin resistance.

Abstract

We compared the ability of commercial and non-commercial, phenotypic and genotypic rapid drug susceptibility tests (DSTs) to detect rifampicin resistance (RR)-conferring 'disputed' mutations frequently missed by Mycobacterium Growth Indicator Tube (MGIT), namely L430P, D435Y, L452P, and I491F. Strains with mutation S450L served as positive control while wild-types were used as negative control. Of the 38 mutant strains, 5.7% were classified as RR by MGIT, 16.2% by Trek Sensititre MYCOTB MIC plate, 19.4% by resazurin microtiter plate assay (REMA), 50.0% by nitrate reductase assay (NRA), and 62.2% by microscopic observation direct susceptibility testing (MODS). Reducing MGIT rifampicin concentration to 0.5 µg/ml, and/or increasing incubation time, enhanced detection of disputed mutations from 5.7% to at least 65.7%, particularly for mutation I491F (from 0.0 to 75.0%). Compared with MGIT at standard pre-set time with 0.25 µg/ml ECOFF as breakpoint, we found a statistically significant increase in the ability of MGIT to resolve disputed mutants and WT strains at extended incubation period of 15 and 21 days, with 0.5 µg/ml and 1 µg/ml ECOFF respectively. MODS detected 75.0% of the I491F strains and NRA 62.5%, while it was predictably missed by all molecular assays. Xpert MTB/RIF, Xpert Ultra, and GenoscholarTB-NTM + MDRTB detected all mutations within the 81 bp RR determining region. Only GenoType MTBDRplus version 2 missed mutation L430P in 2 of 11 strains. Phenotypic and genotypic DSTs varied greatly in detecting occult rifampicin resistance. None of these methods detected all disputed mutations without misclassifying wild-type strains.

• Authors: Gabriela Torrea, Kamela C S Ng, Armand Van Deun, Emmanuel André, Justine Kaisergruber, Willy Ssengooba, Christel Desmaretz, Siemon Gabriels, Michèle Driesen, Maren Diels, Sylvie Asnong, Kristina Fissette, Mourad Gumusboga, Leen Rigouts, Dissou Affolabi, Moses Joloba, Bouke C De Jong
• Journal: Scientific reports (Sci Rep) Vol. 9 Issue 1 Pg. 11826 (08 14 2019) ISSN: 2045-2322 [Electronic] England
• PMID: 31413308 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antitubercular Agents
• Bacterial Proteins
• rpoB protein, Mycobacterium tuberculosis
• DNA-Directed RNA Polymerases
• Rifampin

Topics

• Antitubercular Agents
• Bacterial Proteins (drug effects, genetics)
• DNA-Directed RNA Polymerases (drug effects, genetics)
• Drug Resistance, Bacterial (genetics)
• Genes, Bacterial
• Genotype
• Microbial Sensitivity Tests
• Mutation
• Mycobacterium tuberculosis (drug effects, genetics)
• Rifampin (pharmacology)