Quantification of viable bacterial load in artificial sputum spiked with Mycobacterium tuberculosis

Friedrich, Sven O.; Kolwijck, Eva; Karinja, Miriam N.; Merwe, Lize van der; Diacon, Andreas H.

doi:10.1016/j.tube.2019.03.001

Cited by 1 publication

(2 citation statements)

References 14 publications

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“…Secondly, the direct nature of TLA testing complicates appropriate quality controls, for which fresh sputum is needed, as manipulation of strains on May 10, 2021 by guest http://aac.asm.org/ Downloaded from would increase biosafety requirements. However the use of samples spiked with avirulent strains, compatible with BSL2 hazard containment, could be considered for this purpose [36]. For 4 isolates (2.0%), discordant results could not be explained, and for this reason considered as administrative errors.…”

Section: Discussionmentioning

confidence: 99%

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Thin-Layer-Agar-Based Direct Phenotypic Drug Susceptibility Testing on Sputum in Eswatini Rapidly Detects Mycobacterium tuberculosis Growth and Rifampicin Resistance Otherwise Missed by WHO-Endorsed Diagnostic Tests

Ardizzoni

Ariza

Mulengwa

et al. 2021

Antimicrob Agents Chemother

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BACKGROUND: Xpert®MTB/RIF rapidly detects resistance to rifampicin (RR), however this test misses the I491F-RR conferring rpoB mutation, common in Southern Africa. In addition, Xpert®MTB/RIF does not distinguish between viable and dead Mycobacterium tuberculosis (MTB). OBJECTIVE: To investigate the ability of thin layer agar (TLA) direct drug-susceptibility testing (DST) to detect MTB and its drug-resistance profiles in field conditions in Eswatini. DESIGN: Consecutive samples were tested in parallel with Xpert®MTB/RIF and TLA for rifampicin (1.0 μg/ml) and ofloxacin (2.0 μg/ml). TLA results were compared at the Reference Laboratory in Antwerp with indirect DST on Löwenstein-Jensen or 7H11 solid media and additional phenotypic and genotypic testing to resolve discordance. RESULTS: TLA showed a positivity rate for MTB detection of 7.1% versus 10.0% for Xpert®MTB/RIF. Of a total of 4547 samples included in the study, 200 isolates were available for comparison to the composite reference. Within a median of 18.4 days, TLA detected RR with 93.0% sensitivity (CI-77.4-98.0) and 99.4% specificity (CI 96.7-99.9), versus 62.5% (CI 42.7-78.8) and 99.3% (CI 96.2-99.9) for Xpert®MTB/RIF. Eight isolates, 28.6% of all RR confirmed isolates, carried the I491F mutation, all detected by TLA. TLA also correctly identified 183 of the 184 ofloxacin-S isolates (99.5% specificity, CI 97.0-99.9). CONCLUSIONS: In field conditions, TLA rapidly detects RR, and in this specific setting contributed to detection of additional RR patients over Xpert®MTB/RIF, mainly but not exclusively due to I491F. TLA also accurately excluded fluoroquinolones resistance.

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Section: Discussionmentioning

confidence: 99%

“…Second, the direct nature of TLA testing complicates appropriate quality controls, for which fresh sputum is needed, as manipulation of strains would increase biosafety requirements. However, the use of samples spiked with avirulent strains, compatible with BSL2 hazard containment, could be considered for this purpose ( 32 ).…”

Section: Discussionmentioning

confidence: 99%