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Diagnostic accuracy of the LiquidArray MTB-XDR VER1.0 for the detection of Mycobacterium tuberculosis complex and fluoroquinolone, amikacin, ethambutol, and linezolid resistance

E Auma(1) R Alberts(1) B Derendinger(1) R Venter(1) E M Streicher(1) S Pillay(1) Y T Ghebrekristos(1,2) M Mburu(3) M Ruhwald(3) R M Warren(1) A Penn-Nicholson(3) G Theron(1) M de Vos(3)

1:DST-NRF Centre of Excellence for Biomedical Tuberculosis Research, SA MRC Centre for Molecular and Cellular Biology, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa; 2:National Health Laboratory Service, Greenpoint Tuberculosis Laboratory, Cape Town, South Africa; 3:FIND, Geneva, Switzerland

Rapid drug susceptibility testing (DST) for fluoroquinolones and linezolid is crucial to confirm eligibility for the new shorter regimens for rifampicin-resistant tuberculosis (TB). We assessed the diagnostic accuracy of Bruker/Hain Lifescience LiquidArray MTB-XDR (LA-XDR) for the detection of Mycobacterium tuberculosis complex (MTBC) and mutations associated with resistance to fluoroquinolones, linezolid, ethambutol and amikacin. For evaluation we used residual diagnostic specimens from people with presumptive TB in South Africa and well characterised drug-resistant specimens from the FIND Specimen Bank. Liquid culture was used as reference standard for MTBC detection, while phenotypic DST and Sanger sequencing were used as composite reference standard for resistance detection.

In total 720 specimens were available for the evaluation. LA-XDR showed an overall sensitivity of 85% (95% CI, 80-89) and specificity of 99% (95% CI, 98-100) for the detection of MTBC. In smear-negative specimens, sensitivity was 79% (95% CI, 71-85). For fluoroquinolone and ethambutol resistance detection, LA-XDR sensitivity was 94% (95% CI, 86-98) and 85% (95% CI, 75-91), respectively. Sensitivity for amikacin resistance detection was 55% (95% CI, 34-74), due to the inclusion of specimens in which resistance was conferred by eis promoter mutations, which are not included in the LA-XDR design. LA-XDR was able to detect linezolid resistance conferring mutations in 6/7 linezolid phenotypic-resistant cultured isolates.

LA-XDR met minimal WHO TPP criteria for the detection of MTBC and has the potential to provide rapid DST for two key second-line drugs, linezolid and fluoroquinolone, which may allow for rapid initiation of appropriate regimens to improve treatment outcomes. 

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