FIG. 2.

Minimum detectable fraction of mutant DNA. DNA extracted from RIF-resistant and RIF-susceptible M. tuberculosis isolates were mixed to six final concentrations of mutant DNA. Mutant DNA contained either an rpoB 531ttg mutation (A) or an rpoB 533ccg mutation (B). Sample mixtures equivalent to 20 times the assay limit of detection (LOD) of 4.5 genomes per reaction were added to the chamber receiving eluted DNA in the full cartridge protocol and were processed using a PCR-only protocol. The percentage of samples (n = 20) identified as RIF resistant was plotted at each concentration. As determined by logistic regression, there was a 95% probability of detecting RIF resistance when the DNA mixture contained 61.2% or 100% of the total DNA in the sample mixture for a 531ttg and 533ccg mutant, respectively. The curves from top to bottom indicate the upper, middle, and lower bounds of the 95% CI. Dashed lines indicate limit of detection.