Abstract
BackgroundA new direct microplate-based colorimetric drug susceptibility test that omits the initial isolation of Mycobacterium tuberculosis from sputum specimens was evaluated.MethodsA total of 51 M. tuberculosis acid fast bacilli (AFB) smear-positive sputum specimens were inoculated directly into drug-free and serial dilutions of drug-containing Middlebrook 7H9 broth media. With this direct resazurin micro plate assay (REMA) method, resazurin dye was used as a growth indicator in microplate wells. The minimum inhibitory concentrations (MIC) of isoniazid (INH) and rifampicin (RIF) were compared with those of the ‘gold standard’ absolute concentration method (ACM). The turnaround time (TAT) of the direct REMA and the ACM were also determined.ResultsAt the selected cut-off points (INH: 0.0625 μg/mL; RIF: 0.125 μg/mL), good drug susceptibility test results were obtained for INH and RIF with an average sensitivity, specificity and accuracy of 90%, 100% and 97%, respectively, with a TAT of 15 days. The REMA method also correctly classified the resistant isolates with positive predictive values of 95% and negative predictive values of 98% for the two drugs.ConclusionsThe direct REMA was reliable in routine diagnostic laboratories for the drug susceptibility testing of M. tuberculosis and the rapid detection of multi-drug-resistant tuberculosis.
Highlights
Tuberculosis (TB) continues to be a major public health problem in developed and developing countries
A visual reading of the direct resazurin micro plate assay (REMA), which was the best method for distinguishing resistant and susceptible strains, indicated that the minimum inhibitory concentrations (MIC) cut-off points for the INH and the RIF were 0.0625 μg/mL and 0.125 μg/mL, respectively
Of the 51 M. tuberculosis isolates tested with the absolute concentration method (ACM), 41 were susceptible to INH, and 10 were resistant
Summary
Tuberculosis (TB) continues to be a major public health problem in developed and developing countries. An estimated two billion people have the disease [1]. There were an estimated 1.4 million TB deaths in 2015. The number of TB deaths fell by 22% between 2000 and 2015, the disease remained one of the top 10 causes of death worldwide in 2015 [3,4]. Over the past five years in Malaysia, there has been a steady increase in the number of TB notifications: approximately 52–81 per 100,000 people between 2013 and 2017, with an increased rate of 1%–7% annually until 2016 [5,6]. The development of multi-drug resistant Mycobacterium tuberculosis (MDR-TB) and the recent emergence of extensively drug resistant. A new direct microplate-based colorimetric drug susceptibility test that omits the initial isolation of Mycobacterium tuberculosis from sputum specimens was evaluated
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