Table 1.
Characteristics of three molecular methods (Logix Smart MTB, Cobas MTB, and Xpert MTB/RIF Ultra) and their processing for the diagnosis of tuberculosis.
| Characteristics | Logix Smart MTB | Cobas MTB a | Xpert MTB/RIF Ultra |
|---|---|---|---|
| Number of samples per processing | 32 concentrated samples | 20 concentrated samples (maximum capacity of 90 samples) | 16 concentrated samples (by GeneXpert® XVI platform) |
| Type of conventional samples | Sputum, airway fluids | Sputum, sputum sediments, or BAL with NALC-NaOH | Sputum or Sputum sediments |
| Detection target | Presence of IS6110 and MPB64 genes | Presence of esx genes and 16S rARN gene/Mutation in rpoB, katG and inhA genes | Presence of IS6110 and IS1081 genes/rpoB gene mutation |
| Detection limit | 8 copies/μL | 7.6 UFC/mL | 15.6 UFC/mL |
| Minimum sample quantity | 200 µL | 1000 µL | 500 µL |
| Sample pretreatment | Liquefaction with reagents inside the plate + proteinase K | Inactivaction + liquefaction with MIS and sonication | Liquefaction with sample reagent (composed of sodium hydroxide and isopropanolol) |
| Extraction type | Magnétic beads in HollySys Extraction Kit b | Magnetic beads in Cobas 6800 | Sonication |
| Treatment and extraction time | 30 min | 150 min | 20 min |
| Conservation temperature | HollySys between 4–30°C. For Logix Smart, below −15°C | 2–8°C | 2–28°C |
| Preparation time for amplification | 40 min | 20 min | 1 min |
| Type of PCR | qPCR | qPCR | semi-nested qPCR |
| Amplification time | 80 min | 180 min | 90 min |
| Results information | Qualitative presence of mycobacteria | Qualitative presence of mycobacteria. Determines resistance to R and H | Qualitative presence of mycobacteria. Determines resistance to R |
a
If positive samples exist another detection kit for rifampicin and isoniazid that meets the same parameters would be run.
b
Components on the HollySys plate are Guanidine Hydrochloride, Sodium Chloride, SDS, Tris-HCl, Isopropanolol, and absolute ethanol.
BAL, bronchoalveolar lavage; H, isoniazid; MIS, Cobas® Microbial Inactivating Solution; MTB, Mycobacterium tuberculosis; NALC-NaOH, N-acetyl-L-cysteine-sodium hydroxide; qPCR, Real-time polymerase chain reaction; R, rifampin; rRNA, ribosomal ribonucleic acid.