Candida spp.

MICROBIOLOGY

• Thin walled, ovoid yeast cells typically 4-6 mcm in size, (C. glabrata smaller).
• >150 spp., but ~9 are frequent pathogens in humans, including C. albicans, C. krusei, C. glabrata, C. parapsilosis, C. tropicalis, C. dubliniensis, & C. lusitaniae.
• Microscopy of clinical specimens reveals yeast forms & pseudohyphae w/ some true hyphae. Gram stain: large gram + cocci.
• Grow well in routine blood Cx bottles and on agar plates. Blood cultures positive in 50-70% of candidemia cases. Antigen (e.g. beta-D-glucan) and PCR assays may be of some help for diagnosis of candidemia. C. albicans & C. dubliniensis germ-tube positive (early hyphal-like extensions at 24hrs of culture). All other Candida spp. germ tube negative. PNA-FISH testing on a positive blood Cx: rapid detection of C. albicans and C. glabrata.
• C. albicans found as part of normal flora of mouth, vagina, GI tract. C. parapsilosis associated with central line infections and outbreaks from transmission from healthcare workers. C. tropicalis associated with poor outcomes in severely immunocompromised (i.e. neutropenic) hosts. C. glabrata and C. krusei associated with prior exposure to azoles.