Can molecular methods detect 1% isoniazid resistance in Mycobacterium tuberculosis?

Area of Science:

• Microbiology
• Infectious Diseases
• Antimicrobial Resistance

Background:

• Heteroresistance, the co-existence of drug-susceptible and drug-resistant bacteria, poses a challenge in treating infections.
• Mycobacterium tuberculosis (M. tuberculosis) infections can exhibit heteroresistance, complicating treatment regimens.
• Isoniazid is a first-line drug for tuberculosis, and resistance can significantly impact treatment outcomes.

Purpose of the Study:

• To evaluate the sensitivity of different diagnostic methods in detecting low proportions of isoniazid-resistant Mycobacterium tuberculosis in mixed bacterial populations.
• To compare the performance of conventional drug susceptibility testing (DST) with molecular methods like line probe assay (LPA) and sequencing for heteroresistance detection.

Main Methods:

• Preparation of artificial mixtures containing known proportions of isoniazid-susceptible and isoniazid-resistant Mycobacterium tuberculosis strains.
• In vitro drug susceptibility testing using conventional methods.
• Detection of resistance using line probe assay (LPA) and DNA sequencing.

Main Results:

• Conventional drug susceptibility testing demonstrated high sensitivity in detecting the presence of resistant bacteria, even at a 1% proportion in mixtures.
• Line probe assay and sequencing methods were unable to detect the 1% proportion of isoniazid-resistant Mycobacterium tuberculosis strains.
• The study highlights a significant gap in the detection capabilities of molecular methods for clinically relevant levels of heteroresistance.

Conclusions:

• Conventional drug susceptibility testing remains the most sensitive method for detecting heteroresistance in Mycobacterium tuberculosis.
• Current molecular diagnostic tools may not be sufficiently sensitive to identify low-frequency resistant populations, potentially impacting clinical management.
• Further development of sensitive molecular diagnostics is needed to accurately identify heteroresistance in M. tuberculosis infections.