A slow-growing buff-coloured colony appears on Lowenstein-Jensen medium after 4 weeks from a sputum sample. Which rapid test confirms that the isolate belongs to the M. tuberculosis complex rather than a nontuberculous mycobacterium?

• A Growth on para-nitrobenzoic acid (PNB) containing medium
• B Tween 80 hydrolysis test
• C 68 degree Celsius catalase test
• D Immunochromatographic detection of the MPT64 antigen from colony suspension ✓

Explanation

MPT64 is a protein secreted almost exclusively by members of the M. tuberculosis complex, and commercial immunochromatographic strips give a result within hours from a colony emulsion. Growth on PNB argues against the complex but requires further weeks of incubation. The 68 degree catalase and Tween 80 hydrolysis tests help separate nontuberculous species but are slower and less specific, and some rapidly growing mycobacteria complicate their interpretation.

Reference: Koneman's Color Atlas and Textbook of Diagnostic Microbiology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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