Clinical Pathology: General Principles, Microbiology

745) A 17-day-old neonate became febrile and had an elevated white blood cell count. This premature infant was found to have congenital gastrointestinal abnormalities on delivery and was placed on parenteral nutrition. Blood cultures became positive after 48 hours of incubation, and Gram stain demonstrated yeast-like cells (Figures 1 and 2). Repeated subcultures of the positive bottle on routine bacteriologic media failed to recover the organism. Which one of the following is the most likely etiologic agent?

Malassezia furfur is a component of the normal skin microbiota in most individuals. Two major risk factors for infection with M. furfur are catheter-related fungemia in patients receiving total parenteral nutrition, which is high in lipids, and skin diseases, such as Pityrosporum folliculitis, pityriasis (tinea) versicolor, and atopic dermatitis.

• KOH preparations of skin infections with M. furfur demonstrate hyphae and spherical yeast cells and demonstrate a “spaghetti and meatball” appearance (see the figures).

• All Malassezia species require long-chain fatty acids for growth, with the exception of M. pachydermatis.

Malassezia colonies appear cream colored to yellowish-brown and grow best at 30-35°C.

• Microscopically, Malassezia appears as phialides with small collarettes (Figure 2). Identification to the species level is best obtained by using molecular methods, such as sequencing.

• For skin infections, oral ketoconazole or itraconazole are commonly used for treatment. For systemic disease, amphotericin B is the drug of choice. Removing the catheter is critical for treating catheter-related infections.

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