Skin scrapings from a patient with hypopigmented macular lesions on the trunk show a 'spaghetti and meatballs' appearance on KOH mount. The organism fails to grow on Sabouraud dextrose agar unless the medium is overlaid with olive oil. What is the reason for this culture requirement?

• A Olive oil inhibits contaminating bacteria that otherwise overgrow the slow-growing fungus
• B Olive oil provides the acidic pH required for conversion of yeast to hyphal form
• C The organism is an obligate intracellular pathogen dependent on host cell lipids
• D The organism requires an exogenous source of long-chain fatty acids because it lacks enzymes for their synthesis ✓

Explanation

Malassezia furfur, the cause of pityriasis (tinea) versicolor, is a lipid-dependent yeast. It cannot synthesise medium-chain and long-chain fatty acids de novo, so media such as Dixon agar or SDA overlaid with olive oil are needed for isolation. The KOH appearance of short curved hyphae with clusters of round spores gives the classic spaghetti and meatballs picture. Option B is wrong because pH manipulation plays no role, and option A is wrong because the oil is a growth supplement, not a selective inhibitor.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.