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Rapid method for testing susceptibility of Mycobacterium tuberculosis by using DNA probes
N Martin-Casabona1, D Xairó Mimó, T González
1Servei de Microbiologia i Parasitologia, Ciutat Sanitària Universitària Vall d'Hebron, Barcelona, Spain.
Journal of Clinical Microbiology
|October 8, 1997
Summary
This study shows a rapid bioluminescence method using DNA probes can effectively screen for multidrug-resistant tuberculosis strains. The assay demonstrates high accuracy, offering a valuable tool for faster susceptibility testing.
Area of Science:
- Microbiology
- Molecular Diagnostics
- Infectious Diseases
Background:
- Rising multidrug-resistant Mycobacterium tuberculosis strains necessitate rapid susceptibility testing methods.
- Existing methods for tuberculosis susceptibility testing can be time-consuming.
Purpose of the Study:
- To evaluate a commercially available DNA-bioluminescence-labelled probe assay for rapid susceptibility testing of Mycobacterium tuberculosis.
- To determine the correlation between bioluminescence signals, bacterial counts, and turbidity.
- To standardize and validate the method for detecting resistance to isoniazid and rifampin.
Main Methods:
- Correlation study of photometric light units (PLUs) with colony-forming units (CFU) and turbidity over 14 days.
- Standardization of the method using 20 isoniazid-resistant and 18 rifampin-resistant strains, determining optimal inoculum and reading times (3 and 5 days).
- Validation of the standardized method on 117 clinical isolates using isoniazid and rifampin.
Main Results:
- A strong correlation (r > 0.9) was observed between PLUs, CFU, and turbidity from day 3 onwards.
- Standardization identified optimal parameters using a 10(-2) dilution and readings at 3 and 5 days, establishing a cutoff quotient for resistance.
- On day 5, the assay achieved 96.2% sensitivity and 100% specificity for detecting resistant strains.
Conclusions:
- The DNA-bioluminescence probe method is a readily available and easy-to-perform technique.
- This assay shows high accuracy and potential utility for the rapid screening of drug-resistant Mycobacterium tuberculosis.
- The method offers a significant improvement in speed compared to traditional susceptibility testing.