The microscopic observation drug susceptibility (MODS) assay is a rapid, low-cost method for simultaneous detection of Mycobacterium tuberculosis and drug resistance from sputum. Which of the following correctly describes the principle of this assay?

• A Detection of specific rpoB gene mutations by real-time PCR
• B Measurement of IFN-gamma released by T cells in response to TB antigens
• C Hybridisation of amplified mycobacterial DNA to probes on a nitrocellulose strip
• D Visual detection of characteristic cording growth of MTB in liquid culture under inverted microscope, with and without drugs ✓

Explanation

MODS is based on the early recognition of the characteristic cording growth of M. tuberculosis in Middlebrook 7H9 liquid culture using an inverted light microscope. Drug-containing and drug-free wells are compared for growth, giving simultaneous DST results in a median of 7 days. It does not require molecular probes or PCR. The LPA distractor describes line probe assay, and the IFN-gamma distractor describes IGRA.

Reference: Mackie and McCartney Practical Medical Microbiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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