Acridine orange (AO) stain is used in microbiology primarily to detect:

• A AFB in sputum — superior to Ziehl-Neelsen for HIV-positive patients
• B Fungal elements in tissue — superior to KOH for subcutaneous mycoses
• C Clue cells in bacterial vaginosis diagnosis under dark-field microscopy
• D Low-density bacteraemia in blood cultures — detects nucleic acids in both bacteria and malaria parasites by fluorescence ✓

Explanation

Acridine orange is an intercalating fluorescent dye that binds to both DNA and RNA. It is used in blood culture smears (and thick blood films) to detect low-density bacteraemia and malaria parasites with higher sensitivity than Giemsa in early/low parasitaemia infections. Bacteria and parasites fluoresce orange/red under UV light while background cells appear green. For AFB detection, auramine-rhodamine (not AO) is the fluorescent equivalent of ZN stain. KOH and calcofluor white are used for fungal elements. Clue cells are seen on wet mount/Gram stain.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.