Luciferase reporter phage phAE85 for rapid detection of rifampicin resistance in clinical isolates of Mycobacterium tuberculosis

ABSTRACT

OBJECTIVE@#To evaluate luciferase reporter phage (LRP) phAE85 in rapid detection of rifampicin resistance in a region where TB is endemic.@*METHODS@#One hundred and ninety primary isolates on Lowenstein-Jensen medium were tested. Middlebrook 7H9 complete medium with and without rifampicin at 2 μg/mL was inoculated with standard inoculum from suspensions of the clinical isolate. After incubation for 72 h, LRP was added. Following 4 h of further incubation, light output from both control and test was measured as relative light units. Strains exhibiting a reduction of less than 50% relative light units in the drug containing vial compared to control were classified as resistant. Results were compared with the conventional minimum inhibitory concentration method (MIC) of drug susceptibility testing.@*RESULTS@#The two methods showed high level of agreement of 97% (CI 0.94, 0.99) and P value was 0.000 1. The sensitivity and specificity of LRP assay for detection of rifampicin resistance were 91% (CI 0.75, 0.98) and 99% (CI 0.95, 1.00) respectively. Time to detection of resistance by LRP assay was 3 d in comparison with 28 d by the minimum inhibitory concentration method.@*CONCLUSIONS@#LRP assay with phAE85 is 99% specific, 91% sensitive and is highly reproducible. Thus the assay offers a simple procedure for drug sensitivity testing, within the scope of semi-automation.