The manual mycobacteria growth indicator tube and the nitrate reductase assay for the rapid detection of rifampicin resistance of M. Tuberculosisin low resource settings

Abstract

BackgroundTuberculosis (TB) is a disease of poverty that contributes significantly to ill-health in developing countries. Drug resistant TB is a major challenge to disease control. Early diagnosis and rapid determination of drug sensitivity is of paramount importance in eradication of TB. Although automated liquid culture based methods are available for rapid detection of drug resistance, the high cost of these tests prevent them from being used routinely in low resource settings. This study compares two phenotypic methods, the manual Mycobacteria Growth Indicator Tube (MGIT) and the Nitrate Reductase Assay (NRA) in liquid medium, with the agar proportion method (APM), the gold standard for susceptibility testing of Mycobacterium tuberculosis.MethodologyFourteen day old M. tuberculosis strains (n=373) grown on solid media were used for drug susceptibility testing by APM, NRA and the manual MGIT method. Rifampicin free and rifampicin incorporated (final concentration, 1 μg/ml) media were inoculated with the recommended concentrations of mycobacterial suspensions and incubated at 37°C in 5% CO2. In the APM, the proportion of colonies in the drug containing medium was determined. In the NRA, the colour change in the medium was compared with a standard colour series after day 6 and day 12 of incubation. Growth in the MGIT was detected using the manual MGIT reader from day 2 onwards. The 2 methods were compared with the gold standard, APM to determine sensitivity and specificity and agreement between the methods was calculated using kappa statistics.ResultsThirty one (31) rifampicin resistant isolates were identified. When compared with the APM, the sensitivity of detection of rifampicin resistance was 85% for the NRA and 93% for the manual MGIT and the specificity was 99% and 100% respectively. Both assays, NRA (κ=0.86) and manual MGIT method (κ= 0.94) were in excellent agreement with the APM. The mean turnaround time for manual MGIT method and NRA were 08 days and 10 days respectively.ConclusionThe NRA in liquid medium and manual MGIT are useful alternatives to APM for drug susceptibility testing of M. tuberculosis in low resource settings.

Selected culture and drug-susceptibility testing methods for drug-resistantMycobacterium tuberculosisscreening in resource-constrained settings

“…The main objective of the article published by Adikaram et al [1] was to evaluate the suitability of the manual MGIT and the NRA for the rapid detection of rifampicin resistance in low-resource settings. Fourteen-day-old M. tuberculosis strains (n = 373) isolated onto solid media were used for DST by APM, NRA in liquid medium and the manual MGIT method.…”

“…To treat MDR-TB and XDR-TB patients, the classic 6-month treatment with first-line anti-TB drugs is not effective anymore, so they must be treated with less efficacious, more toxic and much more costly drugs [1]. The duration of treatment is up to 2 years.…”

“…This article evaluates a recently published article by Adikaram et al, which suggests that Manual Mycobacteria Growth Indicator Tube (MGIT) and the Nitrate Reductase Assay (NRA) in liquid medium agreed well with the agar proportion method (APM) -the gold standard for susceptibility testing of Mycobacterium tuberculosis -for the rapid detection of rifampicin resistance in low-resource settings [1].…”

Sputum induction is a safe procedure to use in prisoners and MGIT is the best culture method to diagnose tuberculosis in prisons: a cohort study

“…The time to detection of a positive culture with MGIT was found to be shorter than with LJ or TLA, in accordance with the results of previous studies. [5][6][7][8][9][10][11][12][13][14] Furthermore, Balabanova et al reported that the concordance between drug susceptibility testing on LJ and MGIT was 96.8% for rifampicin and 95.6% for isoniazid. 28 There are new molecular techniques that perform well, allowing diagnosis on the same day, with the added advantage of providing information about resistance to isoniazid and/or rifampicin.…”

“…These methods have been shown to decrease the mean time to detection of growth to 11-15.1 days. 5,6,9,[11][12][13][14] The method of obtaining a respiratory sample is also critical. In prisons, it is important to employ alternative strategies to obtain a specimen when the patient cannot expectorate or has inadequate sputum (HIV patients or those with a dry cough), during follow-up to confirm that the patient is cured, or for people who are sputum smear-negative.…”