MGIT 960 liquid culture and smear microscopy

After preparing quantitative culture dilutions, the remaining homogenized sputum was decontaminated with a final sodium hydroxide concentration of 1.5% for 15–20 min and centrifuged in a refrigerated centrifuge at 3000 g for 15 min. Digested-decontaminated sputum sediment was re-suspended to 2 mL in phosphate-buffered saline. A 0.05 mL volume of re-suspended specimen was used for concentrated AFB smear microscopy. A 0.5 mL volume of re-suspended specimen was inoculated in MGIT prepared with PANTA (polymyxin B, amphotericin B, nalidixic acid, trimethoprim and azlocillin) according to the manufacturer’s directions. All positive MGIT cultures were identified and contamination was ruled out with AFB smear microscopy and blood agar plates. Instrument-generated time to detection (TTD) in days and hours was recorded for positive cultures.