Mycology I Flashcards
What is the cell wall of fungi made of?
Chitin
What is the predominant sterol in fungi?
Ergosterol
Hyphae
There are a long, branching filamentous structure
Germ Tube
A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination. The germ tube differentiates, grows, and develops by mitosis to create somatic hyphae.
Pseudohyphae
Sausage linked looking hyphae that from from a germ tube
Conidia
Conidia, sometimes termed asexual chlamydospores, or chlamydoconidia are asexual, non-motile spores of a fungus
Arthroconidia
It is when pieces of hyphae break off and each piece becomes spore forming
Phialide
It is a flask-shaped projection from the vesicle (dilated part of the top of conidiophore) of certain fungi.
What are the forms of dimorphic fungi and when are they seen?
- Yeast like cells at 35 C
- Mold form at 25 C
“Yeast in the heat, mold in the cold”
What is the most common opportunistic fungal pathogen?
Candida
Where is Candida found?
Normal flora of GI and GU tracts
What are the only species of Candida that forms germ tubes?
C. albicans and C. dubliensis
What Candida has the highest prevalence from oral or fecal specimens of HIV-positive patients?
C. dubliniensis
What Candida is resistant to fluconazole?
C. glabrata
What in Candida activates the complement system?
Cell wall mannan activates the alternate complement pathway leading to enhanced phagocytosis and killing of Candida
What are the risks for Candida infection?
- Antibiotic therapy
- Corticosteroid use
- Decreased T cell function
- Diabetes
What types of Candida albicans infection can be seen?
- Mucocutaneous
- Skin and nail
- Vulvovaginal
- Urinary tract infection
- Meningitis
- Endophthalmitis
What are the stains for C. albicans?
- Gram stain
- Calcofluor stain
What are the spores typically produced by C. albicans?
Candida albicans, and Candida dubliniensis, are the two Candida spp. that produce a typical asexual spore, chlamydospores
What are the characteristics of aspergillum?
- Rapidly growing mold
- Found in soil, air, construction dust
- Dichotomous branching
- Septate hyphae
What is the angle of branching in Aspergillus?
45˚
What is the most important Aspergillus species?
A. fumigatus
What is the pathogenesis of A. fumigatus?
- Inhale spores / conidia
- Conidia bind to fibronectin
- A. fumigatus inhibits alternate complement pathway and interferes with opsonization
What are some possible clinical manifestations of A. fumigatus infection?
- Allergic aspergillosis
- Fungus ball in pre-existing cavity (TB, emphysema)
- Invasive apergillosis
- Dissemination infection
What are the 2 families of fungi that cause murcomycosis?
Mucoraceae and Cunninghamellacea
Where are the agents of murcomycosis found?
Agents of mucormycosis commonly found on fruit, bread, and in soil and are common components of decaying organic debris
What type of patients does murcomycosis typically occur in?
Immunocompromised
What species is most commonly associated with murcomycosis?
Rhizopus arrhizus
What is the typical pattern and presentation of R. arrhizus invasion?
R. arrhizus have a predilection for invading major blood vessels, with ensuing ischemia, necrosis, and infarction of adjacent tissues, resulting in the production of black pus.
Who is at risk for Rhizopus infection?
Patients with granulocytopenia, hematopoietic stem cell transplant and solid organ transplant recipients, and patients with underlying acidosis.
What are some risk factors for Rhizopus infection?
- Acidotic diabetics
- Malnourished children
- Severely burned patients
- Severe leucopenia
- Immunosuppressive disorders
Rhinocerebral mucormycosis
– Most frequent presentation overall and classically affects diabetics with ketoacidosis
– Usually presents with facial and/or eye pain, proptosis and progressive signs of involvement of orbital structures - death within a few days
What is the best option to make treatment better for murcomycosis?
Early diagnosis
What is the branching angle seen in murcomycosis?
90˚
What are the diagnostic features of murcomycosis?
- Microscopic examination of tissues for broad, non septated hyphae
- Growth is woolly white to grey
- Examination of culture for characteristic sporangia
Dermatophytosis
Fungal Infection of keratinized tissues (skin, hair, nails) caused by a group of specialized fungi, the dermatophytes
What are the 3 genera of dermatophytes?
– Epidermophyton – 2 species
– Microsporum – 16 species
– Trichophyton – 24 species
What does “ringworm” refer to in dermatophytosis?
- Inflammation often greatest at the advancing margin leaving a central area with some clearing
- The name “ringworm” follows from the irregular inflammatory border of the skin lesion
Tinea Pedis
Athlete’s Foot
What is the most common dermatophyte infection?
Tinea Pedis
Tinea Pedis Pathogenesis
• Begins as weeping, peeling lesion between 4th and 5th toes. May extend to other toes
• In toe webs, scaling, fissuring, maceration,
and erythema may be associated with an itching or burning sensation
What are the most common species causing Tinea Pedis?
T. rubrum, T. mentagrophytes, E. floccosum
What are the most common species causing Tinea Capitis?
T. tonsurans
Pathogenesis of Dermatophytes
- Inoculation via minor trauma
- Penetrates stratum corneum and proliferates
- Infection spreads laterally, not deeper
- Spread to other keratinized structures
How are dermatophytes diagnosed?
• Direct exam of leading edge of skin lesion by KOH or calcofluor
• Examine hair under Wood’s light
– Damaged hair fluoresces
– Remove infected hair at shaft for culture
• Culture to rule out other pathogens
