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Updated: Jul 28, 2026
Diagnosing Pulmonary Tuberculosis with the Xpert MTB/RIF Test
Published on: April 9, 2012
GeneXpert MTB/RIF Ultra performance to detect uncommon rpoB mutations in Mycobacterium tuberculosis
Leen Rigouts1, Jelle Keysers2, Reenaers Rabab2
1Institute of Tropical Medicine, Mycobacteriology Unit, Nationalestraat 155, Antwerp, Belgium. lrigouts@itg.be.
Objective:
To investigate the performance of GeneXpert MTB/RIF Ultra to accurately detect rifampicin resistance for less common rpoB mutations that potentially confer phenotypic resistance, we tested 28 such Mycobacterium tuberculosis cultures with Xpert Ultra.
Results:
They represented 22 different (combinations of) rpoB mutations. Of 28 isolates tested, one was reported by Xpert Ultra as "No rifampicin resistance detected", 8 yielded a "Rifampicin indeterminate" result, and 19 were identified as rifampicin resistant. Overall, our results corroborate previous observations on the "Indeterminate" results for mutations at codon 432, while we add Lys446Gln as additional "Indeterminate" result and Pro439Leu as a false rifampicin-susceptible result. Furthermore, we document other uncommon point mutations and indels across the rpoB gene that are mostly correctly identified as rifampicin resistant by Xpert ultra (V3). Taken together, "Indeterminate" results in Xpert Ultra may indicate underlying rpoB mutations within the rifampicin-resistance determining region and thus increase the post-test probability of rifampicin resistance, albeit to an unknown extent.
