Lecture 3: Mycology The World of Fungi Flashcards
What two kingdoms are in the world of fungi
- Yeast (unicellular)
- Mold (multicellular)
Fungal charateristics
- Like all eukaryotic organisms: fungi contain membrane bound organelles
- Have distinct organelles including mitochondria (cell generator), endoplasmic reticulum (manages cellular export) and a membrane bound nucleus
- Sexual (molds) and asexual (yeasts generally by budding and also seen in molds) reproduction
What are Yeasts?
- Yeast colonies look similar to bacterial colonies BUT they are NOT bacteria
- Over 1500 different species in kingdom Fungi
- They are unicellular EUKARYOTIC organisms
- Unlike bacteria which have a fairly rudimentary cellular structure, yeast have much more sophisticated cellular machinery
What is the Fungal Cell Wall
- Cell wall is made of Ergosterol, similar to Cholesterol and is a primary sterol
- Contains cell wall
- No peptidoglycan
- Major structure is Chitin
- Exploited for diagnoses typically
- New drugs use the cell wall as a target
What is the importance of Fungal Cell Structures
- Fungal cell wall contains Ergosterol as the primary sterol
- Gives shape to fungi
- Gives them strength by protecting them from organic solvents and UV light
- Secretes enzymes from their walls - able to hydrolyze sugars for nutrition
How does fungal reproduction work
- Primary reproductive structures are called spores or conidia
- Classification gets complicated because based on size, shape, arrangement are all used to classify the organism
- All pattern recognition
Medically relevant Yeasts
- Candida app (~200 spp)
- Cryptococcus spp (Cryptococcus neoformans): when soil is damaged and people breathe it in, people can get very sick
Medically relevant Molds
- Dermatophytes (~50 spp): ringworm, athletes food @24 they are molds but @37 they turn to yeast
- Zygomycetes
- Hyaline Molds
- Dimorphic Fungi (6 spp)
4 Infection Classifications
- Superficial or cutaneous mycoses (hair, skin, nails infections)
- Subcutaneous mycoses (blood and tissue infections)
- Systemic mycoses (very aggressive, can have dual infections)
- Opportunistic mycoses
Yeast: Candida spp.
- Normal flora of the GI tract and often colonized the skin and the environment
- Leads to infections in immunocompromised individuals (happens mostly in a compromised state)
- Can lead to several infectious aetiologies
- Many risk factors; antibiotics don’t work on fungi, most patients are immunocompromised
Yeast: Cryptococcus spp.
- Most medically relevant species are Cryptococcus neoformans and Cryptococcus gattii
- Typically do not cause infections - but can lead to disease/infection in those with altered immune status or underlying morbidity
- Found in soil and in dried animal faeces - specifically associated with bird poop or guano
- Can lead to pneumonia, fungemia (disseminated), meningitis and cutaneous infection
- Contains a large capsule around the yeast cell - helps it evade immune mediated phagocytosis
6 Dimorphic Fungi
Epidemiology matters
1. Histoplasma capsulatum (Globally)
2. Blastomyces dermatitidis; likes old moist areas + when dirt is disturbed because these spores are in the ground (Southeastern ON, New England)
3. Coccidioides immitis; in sand most will get sick after a sandstorm (in SW USA)
4. Paracoccidioides brasiliensis ( In South America)
5. Sporothrix schleiferi (“gardeners disease” likes thorns)
6. Talaromyces marneffei (Southeast Asia)
Temp dependent dimorphisms (For yeast and mold)
Yeast @ 37 celcius, mold at 25 celcius
Dimorphic Fungal Infections: Histoplasma capsulatum
- Clinical presentation include fever, sweats, weight loss, fatigue, and respiratory symptoms
- CNS involvement in 5-20% of cases of acute disseminated histoplasmosis, presenting as chronic meningitis
- Disseminated disease are rare but seen
Dimorphic Fungal Infections: Blastomyces dermatitidis
- Can lead to ammonia
- Presents as nonspecific febrile acute or chronic pulmonary disease mimicking CAP and/or malignancy
- Ultimately to disseminated disease involving cutaneous, genitourinary, and bony lesions
Dimorphic Fungal Infections: Coccidioides immitis
- Pulmonary involvement and in most cases is asymptomatic
- Symptomatic infection presents with fever, cough, and chest pain and may mimic CAP
- Disseminated disease can occur locally with pleural or pericardial invasion or any organ of the body. Disseminated disease can involves cutaneous, genitourinary, and bony lesions
What is Opportunistic Mycoses + most invasive mold
- Fungi considered “non-pathogenic” but can cause significant illness in the immunocompromised, those with prosthetic/intravascular devices and hematologic malignancies
- Commonly found in soil and in the environment
- Opportunistic infections by molds can result in sinus infections, respiratory diseases and fungemia
- Aspergillus: most common invasive mold
Aspergillus
- Most common invasive mold
- Has become the major cause of morbidity and mortality in immunocompromised patients, with mortality rates as high as 88%
- Almost 2/3 of patients have underlying hematologic disease and have undergone bone marrow transplantation
Examples of Opportunistic Fungi
- Aspergillus
- Penicillium
- Paecilomyces
- Acremonium
- Fusarium
What are Mucorales (Zygomycetes) Molds
- Fast growing fungi characterized by primitive coenocytic (mostly aseptate) hyphae
- Environmental fungi in soil, dung, and vegetative matter
- One of the features of this class of fungi is rapid growth, known as “lid-lifters”
- Extremely aggressive disease as the organism does not respect tissue planes including devastating rhino-orbital infections and wound infections
Antifungal Therapies (5)
Attacks cell wall
1. Lanosterol Synthesis (Terbinafine)
2. Cell wall synthesis (Echinocandins - Caspofungin, micafungin, anidulafungin)
3. Forms Membrane Pores (Polyenes - Amphotericin B, Nystatin
4. Nucleic Acid Synthesis (5-Flucytosine)
5. Ergosterol Synthesis (Azoles - Fluconazole, Ketoconazole, Clotrimazole, Miconazole, Itraconazole, Voriconazole
How does lab detection of fungi work
- Gram stain + additional stains from specimens - may see fungal elements
- Because very thick membrane
- Culture on specialize media - Yeast take 1-3 days, Dermatophytes take 1-3 weeks and systemic fungi can take 3-6 weeks
- Variety of stains used can help identify fungi
3 types of Fungal stains
- KOH
- Calcoflour stain
- Silver stain
Fungal stains: KOH
Dissolves tissue cells leaving the fungal cells intact (so we can see better, clean and clear)
Fungal stains: Calcoflour stain
- Binds to chitin in the fungal cell walls (shows a lot of background)
Fungal stains: Silver strain
- Stains fungi black and provides nice contrast. Typically stains proteins in the fungal cell wall (stains them black, produces a lot of background noise)
