MDR/XDR-TB Colour Test for drug susceptibility testing of Mycobacterium tuberculosis, Northwest Ethiopia

Abstract

Background: Appropriate technology tests are needed for Mycobacterium tuberculosis drug-susceptibility testing (DST) in resource-constrained settings. This study was performed to evaluate the MDR/XDR-TB Colour Test (a colour platethin-layer agar test; TB-CX) for M. tuberculosis DST by directly testing sputum at University of Gondar Hospital. Methods: Sputum samples were each divided into two aliquots. One aliquot was mixed with disinfectant and applied directly to the TB-CX quadrant petri-plate containing culture medium with and without isoniazid, rifampicin, or ciprofloxacin. Concurrently, the other aliquot was decontaminated with sodium hydroxide, centrifuged, and cultured on Lӧwenstein-Jensen medium; the stored M. tuberculosis isolates were then sub-cultured in BACTEC Mycobacteria Growth Indicator Tube (MGIT) 960 for reference DST. Results: The TB-CX test yielded DST results for 94% (123/131) of positive samples. For paired DST results, the median number of days from sputum processing to DST was 12 for TB-CX versus 35 for LJ-MGIT (p < 0.001). Compared with LJ-MGIT for isoniazid, rifampicin, and multidrug-resistant tuberculosis, TB-CX had 59%, 96%, and 95% sensitivity; 96%, 94%, and 98% specificity; and 85%, 94%, and 98% agreement, respectively. All ciprofloxacin DST results were susceptible by both methods. Conclusion:The TB-CX test was simple and rapid for M. tuberculosis DST. Discordant DST results may have resulted from sub-optimal storage and different isoniazid concentrations used in TB-CX versus the reference standard test.

Successful introduction of the Colour Test into inexperienced settings

“…The total agreement between the Colour Test and the MGIT 960 system was excellent with over 95% for all the anti-TB drugs tested (Fig 4). Furthermore, the specificities found in this study were > 97% for all technicians, which is in good correlation with previous studies using similar methods [23,24,28,36]. The sensitivities varied between the study laboratories being slightly higher in the Lab B for the detection of INH and RIF resistance and higher in the Lab A with 100% for the detection of LVX resistance.…”

“…Hence, the preparations of the media represent a constraint of the CT method. On the other hand, the performance of CT has been evaluated in the role of a direct test for both detection of TB and DST [25][26][27][28]. Furthermore, CT has been studied as a method for indirect DST on multidrug resistant (MDR)-TB isolates with promising results [23,29].…”

A successful introduction to a non-expert setting of the thin-layer agar Colour Test as an indirect phenotypic drug susceptibility test for Mycobacterium tuberculosis

“…The total agreement between the CT and the MGIT 960 system was excellent with over 95% for all the anti-TB drugs tested (Figure 4). Furthermore, the specificities found in this study were >97% for all technicians, which is in good correlation with previous studies using the method either as a direct or indirect DST (Ardizzoni et al, 2015;Iftikhar et al, 2017;Shibabaw et al, 2020;Toit et al, 2012). The sensitivities varied between the study laboratories being slightly higher in Lab B for the detection of INH and RIF resistance and higher in Lab A with 100% for the detection of LVX resistance.…”

“…In former studies to evaluate the performance of CT the media preparation was carried out in remote expert laboratories (Ardizzoni et al, 2015;Mekonnen et al, 2019). The performance of CT has been evaluated as a direct test for detection of MTB and DST (Mekonnen et al, 2019;Robledo et al, 2006;Satti et al, 2010;Shibabaw et al, 2020) and for indirect DST on multidrug resistant (MDR)-TB isolates, with promising results (Martin et al, 2009;Toit et al, 2012). However, CT has not been evaluated in a non-expert setting coupled with on-site media preparation.…”

New Developments and Insights in the Improvement of Mycobacterium tuberculosis Vaccines and Diagnostics Within the End TB Strategy

“…Although commercial liquid culture-based DST platforms such as BD BACTEC MGIT can provide reliable results within a few days, liquid culture is prone to contamination and requires extensive laboratory infraestructure, specialized personnel, instrument calibration and maintenance, specialized reagents, etc., limiting wide implementation in low-income settings. In contrast, the 1G TB-CX test is based on the rapid, simple and inexpensive thin-layer agar method, and includes DST testing using a four quadrant agar plate, allowing for the early detection of MDR and pre-XDR strains (average of 13 days when compared to the 50 days required for a standard DST), with a 94% sensitivity [59,60]. Despite a limited number of studies in very specific settings, the 1G TB-CX test, at the cost of US$1.35, has the potential to be a good alternative method for the fast and low-cost diagnosis of DS and MDR TB in countries with poor health infraestructure [59].…”