title: Propidium monoazide and Xpert MTB/RIF to quantify Mycobacterium tuberculosis cells.
abstract: Propidium monoazide (PMA) penetrates non-viable cells with compromised membranes. PMA has been proposed to improve the specificity of Xpert MTB/RIF (Xpert) for the detection of viable Mycobacterium tuberculosis. This study assessed the effect of PMA on Xpert cycle thresholds (CT) of M. tuberculosis made non-viable under antibiotic pressure. In vitro, we measured the difference between CTwith and without PMA (ΔCT) in liquid cultures treated with one of six anti-tuberculosis drugs (isoniazid, rifampin, pyrazinamide, ethambutol, streptomycin, moxifloxacin) and found significant ΔCTonly with isoniazid and ethambutol for pan-susceptible M. tuberculosis and only with ethambutol for extensively drug-resistant M. tuberculosis. In the clinic we assessed ΔCTin sputum samples collected from patients with pulmonary tuberculosis before and at regular intervals over 12 weeks after initiation of treatment. Before treatment start, estimated CTwere 19.3 (95% CI: 17.1-21.4) and 19.8 (95% CI: 17.6-22.1) without and with PMA, respectively. Under treatment CTincreased by 2.54 per √√day (95% CI: 1.38-3.69) without PMA and an additional 0.55 per √√day (95% CI: 0.37-0.74; p < 0.0001) with PMA. We conclude that PMA increases the specificity of Xpert for viable M. tuberculosis but the effect is small and dependent on the antibiotics used.
authors.affiliation: Division of Molecular Biology and Human Genetics, MRC Centre for Tuberculosis Research, DST/NRF Centre of Excellence for Biomedical Tuberculosis Research, Faculty of Medicine and Health Sciences, Stellenbosch University, Tygerberg, South Africa; Task Applied Science, Bellville, Cape Town, South Africa.
authors.forename: Xavier A
authors.initials: XA
authors.lastname: Kayigire
authors.affiliation: Division of Medical Physiology, MRC Centre for Tuberculosis Research, DST/NRF Centre of Excellence for Biomedical Tuberculosis Research, Faculty of Medicine and Health Sciences, Stellenbosch University, Tygerberg, South Africa; Task Applied Science, Bellville, Cape Town, South Africa.
authors.forename: Sven O
authors.initials: SO
authors.lastname: Friedrich
authors.affiliation: Task Applied Science, Bellville, Cape Town, South Africa.
authors.forename: Miriam N
authors.initials: MN
authors.lastname: Karinja
authors.affiliation: Task Applied Science, Bellville, Cape Town, South Africa.
authors.forename: Lize
authors.initials: L
authors.lastname: van der Merwe
authors.affiliation: Perinatal HIV Research Unit, MRC Soweto Matlosana Collaborating Centre for HIV/AIDS and TB Research, DST/NRF Centre of Excellence for Biomedical Tuberculosis Research, University of the Witwatersrand, Johannesburg, South Africa.
authors.forename: Neil A
authors.initials: NA
authors.lastname: Martinson
authors.affiliation: Division of Medical Physiology, MRC Centre for Tuberculosis Research, DST/NRF Centre of Excellence for Biomedical Tuberculosis Research, Faculty of Medicine and Health Sciences, Stellenbosch University, Tygerberg, South Africa; Task Applied Science, Bellville, Cape Town, South Africa. Electronic address: ahd@sun.ac.za.
authors.forename: Andreas H
authors.initials: AH
authors.lastname: Diacon
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000995:Antitubercular Agents / Q000494:pharmacology / Q000627:therapeutic use; D001386:Azides / Q000378:metabolism / Q000494:pharmacology*; D004269:DNA, Bacterial / Q000378:metabolism; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D050296:Microbial Viability / Q000187:drug effects; D008875:Middle Aged; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000302:isolation & purification*; D011419:Propidium / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction / Q000379:methods; D012680:Sensitivity and Specificity; D013048:Specimen Handling / Q000379:methods; D013183:Sputum / Q000382:microbiology; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis* / Q000188:drug therapy / Q000382:microbiology; D055815:Young Adult
chemical_list: D000995:Antitubercular Agents; D001386:Azides; D004269:DNA, Bacterial; C533957:propidium monoazide; D011419:Propidium
keywords: Mycobacterium tuberculosis; Propidium monoazide; Xpert MTB/RIF