Oleic albumin dextrose catalase supplement

Sputum samples from culture and smear-negative patients with no history of previous TB were combined, diluted in sample buffer, and spiked with M. tb H37Rv at 1500, 750, 375, 188, 94, 47, 24, 12, 9 , 5 and 0 CFUs/ml. Each dilution of spiked sputa was tested using the Xpert MTB/RIF, and Xpert Ultra assay in triplicate, and the results were compared at each concentration. Dilutions were plated onto Middlebrook 7H9 agar (Sigma, Germany) containing oleic albumin dextrose catalase (OADC) supplement (Becton Dickinson, USA), and colony forming units (CFUs) were counted to ensure that the spiked levels of CFU/ml were accurate.
The effect of serial freeze-thaw cycles on Xpert performance Samples classified as smear-negative Xpert MTB/RIF-positive and culture-positive (n = 16) were randomly selected from biobanked samples to evaluate whether freeze-thawing the sample has an effect on test performance. The samples underwent three complete freeze-thaw cycles, after which Xpert MTB/RIF was performed as described previously. The cyclic threshold (Ct) values were compared to previously documented Xpert MTB/RIF results using a fresh sample at the same time of sample collection.