Fungi Flashcards
Fungi
eukaryotic heterotrophs, does not have 70S ribosome or peptidoglycan
Antifungal
target beta-glucan, ergosterol, some toxicity to humans since there are fewer molecular targets available
Fungi can grow in
drier, higher-osmotic-pressure, colder environments than bacteria leading to more cutaneous infections and food spoilage
Two main types of fungi
yeast are single celled and reproduce by budding. molds grow in hyphae/mycelia and have complex reproduction. both make new cells by fungal mitosis; yeast and some others have closed mitosis.
asexual spores
five types of asexual spores have distinctive microscopic appearances, used for diagnosis
thermal dimorphism
can grow as mold at 24C and as yeast at 37C. yeast form has more immune-evasive properties, dual cultures can be useful for diagnosis.
immune response to fungal infection
granulomatous, sometimes also suppurative (discharge of pus)
fungal pathogens
most are environmental, little contagion or drug resistance, no eradication
mycotoxicosis
caused by eating fungal toxins (wrong mushroom or spoiled food), not fungal infection
fungal allergies can lead to
asthmatic reaction
fungal infection
diagnosed by PPD, KOH-mount microscopy with fungal stains, culture on Sabouraud’s agar, PCR available for dangerous systemics, serology for epidemiology
Major classes of antifungal agents
polyenes (distrupt fungal membranes at ergosterol insertion sites), azoles (inhibit ergosterol syn), echinocandins (inhibit beta-glucan syn)
Polyenes
highly effective and broad spectrum but toxic - Amphotericin B is the only systemic and is nephrotoxic
Azoles
less toxic, different ones optimally active against different fungi, fluconazole/diflucan major one, treats candidiasis and cryptococcosis
Echinocandins
low toxicity, highly effective against candida and aspergillus
Superficial Mycoses
Caused by fungal growth on the superficial skin layer, Does not require thermal dimorphism, Very common, but symptoms are minor: itch or discoloration, Treated with topical azoles, alt oral griseofulvin
Dermatophytosis
is very common, caused by three different genera of fungi, infect only superficial keratinized structures, produce keratinases, symptoms are called Tinea (jock itch, athlete’s foot, ringworm). Transmitted by fomites or autoinnoculation. Diagnose by KOH mount, culture. Treat all affected body sites simultaneously w/ topical antifungal cream, alt oral griseofulvin.
Subcutaneous Mycoses
Introduced by trauma exposing subcutaneous tissue to soil or vegetation, Slow spread from trauma site toward trunk by lymphatics, Thermal dimorphism, history of ineffective antibiotic treatment, Treated with oral azoles, In serious cases, amphotericin B and local surgery
Sporotrichosis
is caused by Sporothrix spp, thermally dimorphic fungi of vegetation that enters skin through small injuries (thorns, splinters). Painless ulcer at site spreads up lymphatic over years. If COPD, may be pulmonary. If immunosuppressed, may be disseminated, meningitis. Diagnose by biopsy and culture at room temp from pus. Treat normal type with oral azoles, more serious forms with Amphotericin B.
Systemic mycoses
Environmental: spores/fungi in soil, Inhaled into lungs, Thermal dimorphism, Range of severity: asymptomatic clearance to death, NOT person-to-person transmissible, may mimic TB, but source is American dirt, not foreign crowds
Coccidioides
thermally dimorphic (mold/spherule), endemic to US Southwest, mold grows in wet weather, releases infectious arthrospores in dry, spores inhaled, change form. 60% Mild: asymptomatic or flulike clearance by innate or containment by CMI, Moderate: valley fever/ desert rheumatism: pulmonary+EN, severe: major pneumonia or dissemination (either bare or in macrophages). Risk factors: age, race, pregnancy, immunocompromise, occupational high exposure. Diagnose by exam, history, PPD, biopsy for spherules, culture, serology for dissemination. Treat if predisposed to complications (oral azoles), meningitis (fluconazole), pregnant or disseminated (Amphotericin B).
Opportunistic mycoses
Diseases and severity are widely varied, depending on the patients’ pre-existing conditions, Optimal treatment addresses both the infection and the underlying problem
Cryptococcosis
is environmental, enabled by reduced CMI, suppresses host inflammatory response. Presents late in disease with meningitis and skin nodules or pulmonary symptoms. Diagnose by biopsy, CSF, crag. Treat with combinations of azoles and Amphotericin B.
