Ziehl-Neelsen acid-fast staining method is commonly used to demonstrate:

Correct option is A

Ziehl-Neelsen stain is a differential stain used primarily to detect acid-fast organisms like Mycobacterium tuberculosis. These bacteria retain the red dye (carbol fuchsin) even after treatment with acid-alcohol due to their high mycolic acid content. This staining is crucial for diagnosing tuberculosis in sputum samples.
Explanation of options: (a) ✔ Mycobacterium tuberculosis – Acid-fast bacilli visualized using Ziehl-Neelsen stain. (b) ✘ Klebsiella pneumonia – A Gram-negative rod; not acid-fast. (c) ✘ Escherichia coli – Also a Gram-negative bacterium, not acid-fast. (d) ✘ Corynebacterium diphtheriae – A Gram-positive rod, not identified using acid-fast staining.