Rapid screening of Mycobacterium tuberculosis for susceptibility to rifampicin and streptomycin.

OBJECTIVE To investigate rapid detection of drug-resistant tuberculosis using the genotypic Inno-LiPA Rif TB assay and a novel, low-cost, bacteriophage-based susceptibility assay. DESIGN The performance of the microwell phage replication assay (MPRA) on 18 isolates from suspected multidrug-resistant tuberculosis patients was compared to the LiPA assay performed directly on sputum specimens. Mutations in the rpoB gene identified by LiPA that confer resistance to rifampicin (RMP) were confirmed by DNA sequencing, while susceptibilities were confirmed by the proportion method and BACTEC. A further 19 isolates undergoing routine screening for both RMP and streptomycin susceptibility were included for comparison. RESULTS Susceptibility to RMP was determined for 17/18 (94.4%) sputum specimens tested by LiPA. Correlation between MPRA, molecular and conventional methods was 100% for the detection of RMP susceptibility. However, for susceptibility to streptomycin one discrepant result was found: an isolate susceptible to streptomycin by the proportion method was found resistant by MPRA to 2 microg/ml of streptomycin. Similarly, an isolate initially resistant by MPRA upon re-testing was found susceptible in agreement with the conventional 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.