Improved Bactec MGIT 960 Pyrazinamide Test Decreases Detection of False Mycobacterium tuberculosis Pyrazinamide Resistance

摘要

At the SRL in Rome, the PZA M960 assay is performed according to the manufacturer's instructions (14), with minor modifications. Briefly, a positive MGIT tube obtained 1 or 2 days after the positivity signal of the M960 instrument (seed tube) is vortexed for 30 s and then allowed to settle for 20 to 30 min. Thereafter, a 1-ml aliquot of the settled seed tube is taken with a 1-ml pipet from the top surface, instead of lower down. Of this aliquot, 0.5 ml is transferred to the PZA test tube containing 100 μg/ml of PZA and 0.5 ml is transferred to a tube containing 4.5 ml of sterile saline. This 1:10 dilution tube is repeatedly mixed with a new pipet, and 0.5 ml is used to inoculate the tube without PZA (growth control tube). After inversion, both the growth control and PZA test tubes are incubated in the M960 instrument. The seed tube is used first for PZA DST and then for other drugs.