Test 3- Pathogenic Yeast Flashcards
Candida
- >200 species
- Candida albicans is the only significant animal pathogen
- Grows as budding yeast cell in culture and tissues • Hyphae or pseudophyphae may also be seen in tissues
- Culture
- No special requirements
- White, shiny, high‐convex colonies in 24‐48 hours • Grows well at 25°C and 37°C
Candida albicans generals
Worldwide distribution • Natural Habitat
- Commensal of mucocutaneous areas • Intestinal Tract
- Genital Tract
• Endogenous infections due to:
- Immunosuppression
- Prolonged antibiotic therapy
- Concurrent infection
• Malnutrition
Candida albicans- virulence factors
Candida albicans
- Virulence Factors and Pathogenesis
- Neuraminidase- influenza
- Proteases
- Aid in tissue invasion
- Glycoproteins
- Endotoxin‐like activity
- Yeast form colonizes epithelial surfaces
- Transition to (pseudo)hyphal form for tissue invasion
- Inflammatory response is usually neutrophilic (not granulomatous)
—————“Sour crop”
—————-Corrugated yellow‐gray necrotic pseudomembrane
Candida albicans
candida albicans dx
Candida albicans
• Laboratory Diagnosis
- ———Lesional scrapes
- ——— Centrifuged milk (mastitis)
- ——— Biopsy/Tissue in formalin (histopath)
• Microscopy
- ———Gram stain (appears purple‐blue)
- ———KOH preparation
- ——— Stained tissue sections (or cultured samples)
——————–Thin‐walled,oval,buddingyeastcells+/‐(pseudo)hyphae ———-“Germ tube” formation is characteristic
• Isolation and Identification
———- Colonies visible in 24‐72 hours
- ———White/cream, shiny, convex
- ——— “Beery” smell
- ———Specialized media available
- ———— CHROMagar
- —————— C. albicans, C. tropicalis, C. krusei
————- API‐yeast‐Ident- smell like beer
Cryptococcus
>30 species
Cryptococcus neoformans is the only significant
animal (and human) pathogen
Spherical to oval, thin‐walled, budding yeast
Cells are surrounded by a large mucoid polysaccharide capsule
Daughter cells are single and connected to parent by narrow neck
- Four serotypes:
- A: C. neoformans var. grubii (Worldwide; soil/dust)
- B/C: C. neoformans var. gattii * (Associated with decaying eucalyptus wood)
• D: C. neoformans var. neoformans (Worldwide; soil/dust)
Cryptococcus Serotypes
Cryptococcus neoformans
• Natural habitat
- Serotypes A (C. n. var. grubii) and D (C. n. var. neoformans):
- Worldwide in soil and dust
- Skin, mucous membranes, and intestinal tract of normal mammals and birds
• Yeasts are concentrated in pigeon feces (rich in creatinine)
- >1 year survivability
- Serotypes B and C (C. n. var. gattii):
- Subtropical and temperate areas
- Eucalyptus and gum trees, also other trees
Cryptococcus neoformans pathogenesis and virulence factors
Cryptococcus neoformans- CATS WITH UPPER RESPIRATORY DISEASE
Pathogenesis
• Virulence is mainly associated with the large capsule
• Capsule is diminished in high salt/sugar concentration environments
———- Spores may be aerosolized
Productionofcapsuleinitiatedintissues
Anti‐phagocytic
Immunosuppressive
• Other virulence factors: • Phenoloxidase
- Melanin
- Anti‐oxidant
- Protects yeast in oxidants in phagolysosomes
- Phospholipase
- Mannitol
- Pathogenesis (cont’d)
- Lesions
- Rangefromgranulomastomyxomatousneoplasms
- Containcapsularslime,yeastcells,andinflammatorycells
- Route/Spread of infection
- Usuallyrespiratory
- Localized infection in nasalcavityandsinuses • Eventuallymayinvolvebrainandmeninges
- Subcutaneousgranulomas
- Species affected
- CATS:Rhinitis,nasalgranulomas,CNSinvolvement,
ocular/cutaneous infections
• Dogs:Respiratorytractinfections,someocular/cutaneous manifestations
Cattle:Mastitis(rare)
Horses:Nasalgranulomas
Koalas:Respiratorytractinfections,CNSinvolvement
Humans:Similartocats
Cryptococcus neoformans
C. neoformans- dx
Cryptococcus neoformans
- Laboratory Diagnosis
- BE CAREFUL! Zoonotic agent!
- Biosafety hood recommended
- Useful samples:CSF,exudates,milk,tissue/biopsies
- Directmicroscopy
- India ink or nigrosin stains (outlines capsule)
- Mayer’s mucicarmine (stains capsule and cell wall) • Isolation/Culture
- Blood or SabDex agar
- Chocolate agar for enhanced capsule production
Streak as for bacteria, 48 hours – 2 weeks
Aerobic, 37°C (other Crypto. species will not tolerate 37°C)
Smooth, moist, shiny colonies; white to yellowish
Mucoid growth with age
Capsule is less pronounced from culture
Melanin is produced on birdseed agar
• Immunologicalandmoleculardiagnosticsexist
- Treatment
- Fluconazole,itraconazole • 5‐fluorocytosine
- AmphotericinB
Malassezia generals
Malassezia
20 species
Commensal organisms on oily areas of skin and
ears of dogs/cats
• Malassezia pachydermatis is the most significant species in animals
• Otitis externa
• Seborrheic dermatitis
- Feline chin acne
- Small, bottle‐ or peanut‐shaped yeast (broad‐ based bud)
- Reproduce by bud fission (septum detachment)
Malassezia pachydermatis
pathogenesis and dx
Malassezia pachydermatis
• Pathogenesis
Predisposing factors
• Immunosuppression
• Allergic dermatitis
• Hairyand/or pendulous ears
• Virulence factors
•Zymogen(activates complement, damages keratinocytes, inflammation/pruritis)
• Proteases(damageearcanalmucosa)
Lipases(adjust the sebum consistency to a more favorable environment for yeast)- why it can live in ears
• Leads to more sebaceous secretions
Laboratory diagnosis
- Interpretcarefully(normalflora?)
- Consider clinical signs and number of organisms
- Directmicroscopy(Gramstainormethyleneblue) • Isolation
- SabDex agar, 35‐37°C
- Colonies are small, smooth, “wet‐dog” odor
- Moleculartechniques(PCR)allowspeciesdifferentiation(ifneeded)
Dimorphic Fungi
Sporothrix, Blastomyces, Coccidioides, Histoplasma
Dimorphic Fungi growth forms
- Present two growth forms
- Appear as a mold when growing saprophytically in the environment
- Or in culture at 25‐30°C
- Usually the more stable form
- Appear as a yeast in animal tissues
- Or in culture/enriched media at 37°C
- May cause deep or systemic mycosis in animals and humans
- Cultures are biohazardous to laboratory workers. Be careful!
Sporothrix schenkii
- Disease
- Sporotrichosis
- “Rose‐handler’s disease”
- Distribution
- Worldwide (especially tropics and subtropics)
- Hosts
- Horses, dogs, cats, humans
- Natural Habitat
- Wooden posts, rose thorns, dead vegetation, soil
• Site of Lesions
• Subcutaneous nodules, Lymphocutaneous ulcerations
• Lymphatics (especially horses)
Sporothrix schenkii
Sporothrix schenkii
Sporothrix schenkii
Plentiful yeast seen with methylene blue stain (especially samples from cats)
Blastomyces dermatitidis
Blastomyces dermatitidis
microscopic appearance
Blastomyces dermatitidis
- Colonial morphology
- Grows well on SabDex agar (2‐4 weeks)
- Small colonies, white cottony aerial hyphae • Becomes gray or dark brown
• Microscopic appearance
37°C Culture
25°C Culture
- Large round/oval, thick‐walled yeast cells; broad‐based buds
- Appearance varies depending on culture conditions
