Direct Susceptibility Testing of Mycobacterium tuberculosis for Pyrazinamide by Use of the Bactec MGIT 960 System

Abstract

Pyrazinamide (PZA) is a key antituberculosis drug, yet no rapid susceptibility test is commercially available. PZA drug susceptibility testing (DST) was performed directly on sputum samples from 327 patients and compared with the indirect method by using the Bactec MGIT 960 system in the context of patient screening for participation in a drug trial. Compared to standard indirect PZA DST, direct DST was successful in only 59% of cases, but results obtained were highly accurate and available faster. Agreement between the direct and indirect methods varied from 90 to 100% in each laboratory. The median times for obtaining PZA results from the time when the specimen was collected ranged from 11 to 16 days for the direct test and 18 to 95 days for the indirect test across laboratories. The direct method is accurate and reproducible across laboratories. It can be expected to accelerate results in >50% of cases, but it cannot replace indirect DST for PZA. Phenotypic methods remain the gold standard for DST in drug trials. If future studies can optimize the method to decrease the number of uninterpretable results, direct MGIT DST could be the new phenotypic DST standard for clinical trials, providing more rapid detection of resistance to new drugs in experimental regimens.

Immunological detection of pyrazine-2-carboxylic acid for the detection of pyrazinamide resistance in Mycobacterium tuberculosis

“…However, high rates of mortality have been reported when PZA is administered empirically to patients who are infected with PZA-resistant strains [5]. PZA resistance is associated with resistance to other TB medications: current estimates indicate that 50% of MDR-TB cases are also PZA resistant [6][7][8] and, alarmingly, the emergence of Mycobacterium tuberculosis (Mtb) strains resistant to all known anti-TB drugs has been reported [9]. This is likely to be caused by the mismanagement of pharmacological protocols.…”

“…The Wayne test has a long turnaround time, and false-positive (resistance) reporting can occur due to subjective evaluation [ 15 , 19 ]. On the other hand, MGIT-PZA has poor reproducibility, and a moderate to high rate of false resistance reporting due to a low critical concentration of PZA [ 6 , 10 ]. Recently, a Microscopic Observation Drug Susceptibility (MODS) assay that incorporates the Wayne test (MODS-Wayne) has been described [ 20 ] and serves as a testing platform in the present study.…”

“…Analysis of the Mtb genome to detect drug resistance is now encouraged because of its ease of use and a short time to completion. In the case of PZA this approach seeks to identify mutations in the pnc A gene, which codifies for PZAse [ 5 ] However, the clinical utility of this method is reduced by the high variability of mutations along the pncA gene (no hot-spot is reported), the fact that not all mutations impair PZAse activity [ 7 , 14 , 21 ], and the lack of understanding of the relationship between each mutation and phenotypic resistance [ 6 , 10 ]. Naturally-occurring Mtb strains that express PZAse with defective enzymatic activity have been found to be totally or partially resistant to PZA [ 13 ].…”

MODS-Wayne, a Colorimetric Adaptation of the Microscopic-Observation Drug Susceptibility (MODS) Assay for Detection of Mycobacterium tuberculosis Pyrazinamide Resistance from Sputum Samples

“…MODS-Wayne reported a median turnaround time of 18.5 days (range, 14 to 29 days) for PZA-susceptible isolates and 21 days (range, 14 to 25 days) for PZA-resistant isolates for results in R3. Although the MODS-Wayne turnaround time was higher than that reported for direct MGIT-PZA (range, 11 to 16 days), Demers et al (45) reported that 41% (163/398) of the direct MGIT-PZA results were uninterpretable mostly due to growth failure, and most of the indirect tests (i.e., classic Wayne test) require primary isolation of the isolate first, which means that from the time when the specimen was collected until the susceptibility results were obtained, the turnaround time ranged from 18 to 95 days. Total time from sample to results is in fact much shorter for MODS-Wayne, which is a direct test.…”

Novel culture method to diagnose fungal infections with biopsy tissues

“…Mycobacterial culture is the gold standard for M. tuberculosis diagnosis (12). BACTEC MGIT 960 system is an advanced diagnostic tool commonly used for mycobacteria recovery in clinical laboratories worldwide (13-15). A mixture of antibiotic, including polymyxin B, amphotericin B, nalidixic acid, trimethoprim and azlocillin is added to cultures to decrease contamination rate (16).…”