LECTURE - Candida albicans Flashcards
unicellular fungi that reproduce by budding or fission
yeast
yeast infections can be…
endogenous (almost exclusively endogenous; carrying infection yourself then cause infection) or exogenous
T or F. Yeasts are opportunists
T!
Candida species as normal flora
GI tract, oral cavities, and vagina
Candidosis
disease caused by Candida spp. (albicans mainly)
an emerging, antibiotic-resistant Candida organism
C. auris
agar for C. albicans
Sabouraud agar
C. albicans colonies
dry, pasty, white, and opaque
- budding cells that can produce pseudohyphae (produced in tissues; cant necessarily ee nice, unicellular buds) and chlamydospores depending on growth temp and medium on which they are grown
__% to ___% of healthy people have organisms in yeast as part of normal flora
30 to 50
T or F. Most C. albicans infections are exogenous
F, endogenous!
Three conditions to predispose to Candida albicans infections
- compromised skin, excessive moisture, friction; invasive procedures like indwelling catheters
- defects in Th1 mediated immunity (AIDS, cancer, etc.)
- iatrogenic therapies
> loss of normal flora via broad-spectrum antibiotics
> damage to GI, GU, resp tract and loss of neutrophils due to cancer chemotherapy
> changes in hormone levels such as use of BC
three main types of infections in C. albicans
- mucocutaneous
- cutaneous
- systemic candidiasis
mucocutaenous candidiasis
- most common
- thrush, AIDS-associated oropharyngeal candidosis, vulvovaginal candidosis (vaginitis)
cutaneous candidiasis
skin and nails, prolonged exposure to moisture and heat, secondary to bacterial infection or loss of normal flora
systemic candidiasis
- worst one!!
- frequently fatal; nasty to get rid of once it has established; neutrophils VERY important (C. albicans not resistant to phagocytosis if they can be opsonized)
- immunocompromised host; neutropenic, undergoing chemotherapy
- often diagnosed post-mortem (SO MONITORING IS V IMPORTANT)
Treatment of C. albicans
- azole family of anti-fungal drugs (fluconazole, ketoconazole, itraconazole)
- topical treatments (nystatin, clotrimazole) are used for cutaneous or nail infections
- oral drugs used for mucocutaneous candidiasis
- IV drugs (amphotericin B) for severe infections
- yeast cells may remain for 30 days following therapy
- relapse is common (esp. bc ppl don’t stick to length of prescribed med)
Why do we need to process specimen quickly for yeast?
they can proliferate rapidly (esp. in fluids)
CHROMagar
- differential
- can differentiate among diff Candida species
germ tube test
- lab ID for C. albicans
- high protein media is inoculated with a small amount of yeast
- tube is incubated for 2 hrs at 37 degrees C
- a drop of media is examined microscopically under 10X and 40X for germ tubes
sensitivity testing of C. albicans
- used to test for susceptibility to anti-fungal drugs like fluconazole
- standardized inoculum of pure culture incubated in each well containing doubling dilutions of a drug
- plates read visually or spectrophotometrically
- first well with yeast button = MIC (min. inhibitory conctn)
C. albicans virulence factors
** after one of the three conditions that allow infection are met**
- attachment + biofilm formation (tissues and indwelling catheters)
> Hwp1 genes and ALS gene interaction w C-type lectin receptors on host cells
- organism switch from yeast to hyphal form with production of aspartyl proteases and phospholipase that lead to tissue damage and assist invasion
Main PRR involved in recognizing Candida albicans
- mannose-bindng lectin
- membrane-bound C-type lectin receptors macrophage mannose receptor 1 (MMR)
- dendritic cell-specific ICAM-3… (DC-SIGN)
- macrophage-inducible C-type lectin (MINCLE)
- TLR4
- TLR2
- TLR9 in cytosol can recognize fungal DNA
Pathogenesis of C. albicans
- surface glucomannan receptors on the yeast bind to fibronectin covering epithelial cell or to elements of the extracell matrix
- when epithelial surface is lost or C. albicans have invaded beyond it, invasion is associated with formation of hyphae + proteinase production = digests tissue elements
C. albicans tissue invasion
- adhesion to epithelium
- epithelial penetration and invasion by hyphae
- vascular dissemination, which involves…
- hyphal penetration of blood vessels and seeding of yeast cells into the bloodstream;
- endothelial colonization and penetration during disseminated disease
fourth most common organism recovered from blood in hospitalized patients
C. albicans
- it can disseminate widely when entering the bloodstream and can be found in any organ
The Dalmau Test
- for chlamydospores
- test conditions: media, temperature, air, surface tension, length of incubation
thick-walled resting spores
chlamydospores
filamentous growth from Dalmau test
C. parapsilosis
chlamydospores from Dalmau test
C. albicans
segmented pseudohyphae from Dalmau test
C. tropicalis
Biochemical Id methods for Candida
- assimilation
- based on carbs that are used as sole carbon sources
- automated or manual test
- gold standard is API 20C
