Colorimetric method for determining MICs of antimicrobial agents for Mycobacterium tuberculosis

Area of Science:

• Microbiology
• Clinical Diagnostics
• Drug Resistance Studies

Background:

• Accurate antimicrobial susceptibility testing is crucial for effective tuberculosis treatment.
• Traditional methods for determining minimum inhibitory concentrations (MICs) can be time-consuming.
• Rapid and reliable diagnostic tools are needed to combat drug-resistant Mycobacterium tuberculosis strains.

Purpose of the Study:

• To describe and validate a novel colorimetric method for quantifying Mycobacterium tuberculosis susceptibility to key antimicrobial agents.
• To compare the performance of the colorimetric method with the established agar proportion method.
• To establish interpretive criteria for the colorimetric method.

Main Methods:

• Utilized Alamar blue, an oxidation-reduction dye, as a growth indicator for Mycobacterium tuberculosis.
• Determined MICs for isoniazid, rifampin, streptomycin, and ethambutol for 50 M. tuberculosis strains.
• Compared colorimetric MIC results with those obtained from the agar proportion method.

Main Results:

• The colorimetric method provided MIC results within 7 to 14 days for all tested strains.
• High agreement was observed between the colorimetric and agar proportion methods (97% overall).
• Specific agreement rates were 98% for isoniazid, rifampin, and ethambutol, and 94% for streptomycin.

Conclusions:

• The colorimetric method is a rapid, quantitative, and nonradiometric approach for antimicrobial susceptibility testing of Mycobacterium tuberculosis.
• This method demonstrates excellent concordance with the agar proportion method, offering a viable alternative for clinical laboratories.
• The established interpretive criteria facilitate the clinical application of this colorimetric assay for guiding tuberculosis therapy.