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, and C. lusitaniae.
• Microscopy of clinical specimens reveals yeast forms & pseudohyphae w/ some true hyphae. Gram stain: gram positive budding yeast.
• Grow well in routine blood Cx bottles and on agar plates. Blood cultures positive in 50-70% of candidemia cases (beta-D-glucan testing is more sensitive for candidemia).
• C. albicans and C. dubliniensis germ-tube positive (early hyphal-like extensions at 24hrs of culture). All other Candida spp. germ tube negative. PNA-FISH (peptide nucleic acid fluorescence in situ hybridization) testing on a positive blood Cx: rapid detection of C. albicans and C. glabrata.
• T2 magnetic resonance (T2MR) testing FDA approved in September 2014. Test lyses Candida cells, amplfies Candida DNA, and detects amplified DNA using MR technology. Results in 3-5 hours. Pivotal trial showed overall specificity of 99.4% and overall sensitivity of 91.1%. NPV 99.5% (5% prevalence) and 99.0% (10% prevalence).
• Antigen (e.g. beta-D-glucan) and PCR assays may be of some help for diagnosis of candidemia.
• 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.