Discordance across Several Methods for Drug Susceptibility Testing of Drug-Resistant Mycobacterium tuberculosis Isolates in a Single

Given the increases in drug-resistant tuberculosis, laboratory capacities for drug susceptibility testing are being scaled up world-wide. A laboratory must decide among several endorsed methodologies. We evaluated 87Mycobacterium tuberculosis isolates for concordance of susceptibility results across six methods: the L-J proportionmethod, MGIT 960 SIRE AST, Gene/Xpert MTB/ RIF, GenoTypeMTBDRplus line probe assay, MycoTBMIC plate, and a laboratory-developedmycobacteriophage quantitative PCR (qPCR)-based method. Most (80%) isolates were multidrug resistant. Of the culture-based methods, the mycobacterio-phage qPCRmethod was fastest, the L-J proportionmethod was the slowest, and theMGITmethod required the most repeat testing (P< 0.05). For isoniazid (INH), 82 % of isolates were susceptible by all methods or resistant by all methods, whereas fo