Molecular Bacterial Load Assay: A Fast and Accurate Means for Monitoring Tuberculosis Treatment Response

Abstract

BackgroundTuberculosis is a difficult disease to treat. We report a multi-centre performance evaluation of the molecular bacterial load assay (MBLA) that monitors change in patient bacterial load (BL) as they respond to TB therapy.MethodsSmear or Xpert MTB/RIF-positive patients were prospectively monitored for treatment response using MBLA and culture at four sites in Southeast Africa. Treatment response was defined as decline in BL and or rise in time to culture positivity (TTP) or conversion to negative culture status. Positive culture at 5 or 6 months confirmed treatment failure. MBLA-MGIT correlation and association with treatment outcome were determined by Spearman's ρ and logistic regression, respectively.ResultsA total of 1764 serial samples from 178 patients were assessed for treatment response of which 91% were treatment success. Of those who failed treatment (n=17), MBLA detected TB in 82% at 2 months of treatment compared to MGIT 24% and LJ 6%. Mean BL at baseline was 6±1.3log10 CFU/ml falling to zero in 59% of the patients by 3 months of treatment. A corresponding rise in MGIT TTP, 5±3 to 22±11 was observed, r=–0.5, p<0.0001. The rate of sputum clearance (SLOPE) was high among high-burden patients – 1.0log10C-FU/ml than low-burden patients, –0.7log10CFU/ml in the first 2 weeks of treatment. Despite higher rates of clearance, high-burden patients were more likely to be TB-positive at 2 months of treatment, p=0.01(OR 2.5). Response was generally slower among the MDR than susceptible TB patients. Time to result was 4h with MBLA and 5–22 days for MGIT. Contamination was 25% in MGIT and 4% on solid culture.Inter-site testing revealed that MBLA was reproducible, ANOVA p >0.05.ConclusionsMBLA is a contamination-insensitive, reproducible method capable of giving results in real-time. Direct quantification of bacterial load from uncultured sputum demonstrates considerable potential for application in resource-limited settings where TB culture facilities are scarce.

OMNIgene.SPUTUM suppresses contaminants while maintainingMycobacterium tuberculosisviability and obviates cold-chain transport

“…As measures of viability, MGIT TTP and molecular bacterial load are inversely correlated [ 9 , 10 ]. Given the many MGIT negative results, we explored whether this was due to loss of viability by testing the correlation between SDP/OM-S MGIT TTP and bacterial load measured by MBLA among same-day samples.…”

“…A pre-analytical tool that effectively removes contaminating flora from sputum and preserves viable M. tuberculosis would benefit clinical diagnosis and management of TB disease. Viable M. tuberculosis is required for culture and for molecular assays, such as molecular bacterial load assay (MBLA) which quantifies viable M. tuberculosis in sputum [ 9 – 11 ], molecular DST [ 12 ] and genomics [ 13 ]. Unlike PrimeStore transport medium, which eliminates viability by killing M. tuberculosis and is only suitable for downstream molecular assays, OM-S maintains viability important for culture and culture-based DST [ 14 ].…”

Improving diagnosis and monitoring of treatment response in pulmonary tuberculosis using the molecular bacterial load assay (MBLA)

“…This confirms that the test results are reproducible in a high-burden setting. We have shown previously that TB MBLA is species specific confirming the diagnosis 11 14 9 and this provides the healthcare worker with confirmation of the tuberculosis diagnosis.…”

United Kingdom–East and Southern Africa Partnership at the Forefront of Developing the First Ever Test that Measures Patient Tuberculosis Burden in Hours

“…12 Funded by the EDCTP, the first multi-site evaluation of the test was conducted at the University of Malawi College of Medicine, Instituto Nacional de Saude, Kilimanjaro Clinical Research Institute, and NIMR-Mbeya Medical Research Centre in Malawi, Mozambique, and Tanzania, respectively. 6 The study revealed that MBLA results are reproducible in different laboratory settings and that it is superior to existing tools for the long-term follow-up of TB patients and monitoring treatment response (Figure 2). Unlike culture, wherein reported contamination rates were as high as 30% in some settings, MBLA was found to be unsusceptible to contamination and inhibition.…”

“…With funding from the European and Developing Countries Clinical Trials Partnership (EDCTP), partnerships between the UK-based University of St Andrews and research institutions in ES have led to the development of the first ever test -the molecular bacterial load assay (MBLA) -that measures the number of TB bacteria in a patient and reveals if this number is declining as a patient progresses on treatment. 6,7 Assay results are available at the laboratory within 4 hours of sample receipt. Real-time knowl-edge of patient mycobacterial burden and the effectiveness of prescribed medications are crucial for timely clinical decisions on patient management.…”