Rapid pyrazinamide susceptibility testing of Mycobacterium tuberculosis by flow cytometry

The resurgence of tuberculosis along with the increased resistance of Mycobacterium tuberculosis has emphasized the need for timely susceptibility testing for control of the disease. Previous studies have shown that rapid susceptibility testing can be accomplished for isoniazid, ethambutol, and rifampin using the flow cytometric assays. In this study we compared the flow cytometric susceptibility assay with the BACTEC TB 460 and BACTEC MGIT 960 for pyrazinamide (PZA). There was 93% agreement between the BACTEC MGIT 960 and the flow cytometric methods for 100 microg/mL of PZA. Additionally, there was a 95% and 86% agreement between the BACTEC TB 460 and flow cytometric methods for 50 microg/mL and 100 microg/mL of PZA, respectively. These findings show that susceptibility testing by the flow cytometric assay is accurate. Most importantly, susceptibility results by the flow cytometric assay were available 24 h after initiation of the testing procedure. The advantages of simplicity, speed and accuracy make the flow cytometric susceptibility assay an immediate impact technology to improve patient care.