Rapid screening of Mycobacterium tuberculosis for susceptibility to rifampicin and streptomycin

OBJECTIVE: To investigate rapid detection of drug-resistant tuberculosis us ing the genotypic Inno-LiPA Rif TB assay and a novel, low-cost, bacteriopha ge-based susceptibility assay. DESIGN: The performance of the microwell phage replication assay (MPRA) on 18 isolates from suspected multidrug-resistant tuberculosis patients was co mpared to the LiPA assay performed directly on sputum specimens. Mutations in the rpoB gene identified by LiPA that confer resistance to rifampicin (R MP) were confirmed by DNA sequencing, while susceptibilities were confirmed by the proportion method and BACTEC. A further 19 isolates undergoing rout ine screening for both RMP and streptomycin susceptibility were included fo r comparison. RESULTS: Susceptibility to RMP was determined for 17/18 (94.4%) sputum spec imens tested by LiPA, Cor relation between MPRA, molecular and conventional methods was 100% for the detection of RMP susceptibility. However, for sus ceptibility to streptomycin one discrepant result was found: an isolate sus ceptible to streptomycin by the proportion method was found resistant by MP RA to 2 mu g/ml of streptomycin. Similarly, an isolate initially resistant by MPRA upon re-testing was found susceptible in agreement with the convent ional method. CONCLUSION: LiPA enables rapid detection of drug-resistant infection, while MPRA offers simple, low-tech testing of drug susceptibilities that may be appropriate for application in low-income countries.