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

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 2μg/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%h(CI 0.75,0.98)and 99ct(CI0.95,1.00)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 die scope of semi-automation.