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» 首頁 » Microbiology » 研究筆記
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Author: Amelia Virostko
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Important key words or phrases. |
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Important concepts or main ideas.
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1. Fungi Vocabulary
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Yeast: single fungal cell with a rigid cell wall that divides by budding
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Pseudohyphae: long chains of yeast resulting from incomplete separation during budding
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Hyphae: threadlike, branching filaments composed of fungal cells attached end to end
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Molds: multicellular colonies composed of clumps of branching hyphae that produce spores
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Spores: reproducing bodies of molds
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Dimorphic fungi: fungi that can grow as either a mold or a yeast
2. Introduction
- Aerobic eukaryotes free-living in the environment or part of the normal human flora
- Anti-fungal medicines target ergosterol, the key sterol in the fungal cell membrane
- Cell wall antigenic to humans, and some fungi have polysaccharide capsule that protects them from the immune response
3. Histoplasma capsulatum
3.1. Encounter
- Commonly found in the southeastern U.S. that borders the Mississippi River and many tropical countries
- Grows in bird and bat excrement, therefore found in old barns and caves
3.2. Entry
- Small, aerosolized spores are inhaled
- Transform into yeast when exposed to normal body temperature
3.3. Damage and Clinical Manifestations
- Often asymptomatic or resembles a minor respiratory illness
- Mild pneumonia can case lung infiltrates and calcified granulomas
- Disseminated disease can occur in immunocompromised hosts, that can cause meningitis, bone lytic granulomas, and skin granulomas
3.4. Key Virulence Factors
- Damage caused by direct invasion and displacement rather than toxins
3.5. Identification and Diagnosis
- Found within histiocytes and granulomas
- Lung biopsy can be performed and stain specimen with Silver stain
3.6. Treatment
- Acute infection does not require treatment
- Chronic or disseminated infections require itraconazole or Amphotericin B
- Resistance is not a problem
3.7. Outcome
- Usually self-limited infection or response to treatment
- Can be chronic or life-threatening in immunocompromised hosts
4. Blastomyces dermatiditis
Rarest form of systemic fungal infection and most likely to become chronic and disseminated
4.1. Encounter
- Anywhere in the U.S. independent of bird or bat excrement
4.2. Spread
- Similar to Histoplasma
4.3. Damage and Clinical Manifestations
- Tends to present in disseminated form than Histoplasma
- Present with weight loss, night sweats, lung involvement and skin ulcers
4.4. Identification and Diagnosis
- Large yeast that divide by broad based budding
4.5. Treatment
- Itraconazole, ketoconazole, or amphotericin-B
5. Coccidioides immitis
- Dimorphic yeast that enters by inhalation
- Causes San Joaquin Valley fever
- 60% of infections are asymptomatic or present as a mild upper respiratory tract infection
- 35% develop symptoms 1-3 weeks after exposure in bones, joints, and/or skin
- Symptoms include: cough, sputum production, chest pain, fever, chills, night sweats, anorexia, weakness, erythema nodosum, and arthralgia
- Meningitis can occur within 6 months and presents with headache
- Disseminated infection occurs with increased frequency in African-Americans and Filipinos, and pregnant women
- Similar to Histoplasma in its mode of entry, spread, damage, diagnosis, and treatment
6. Opportunistic Fungi: Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus
Infect immunocompromised hosts or neutropenic patients
6.1. Candida albicans
6.1.1. Encounter
- Part of normal flora
- Patients at high risk are patients with malignancies, organ or bone transplants, AIDS, burns, operations, trauma, long-term use of IV or intra-arterial catheters, or being treated with broad spectrum antibiotics
6.1.2. Spread
- Phagocytosis by neutrophils is the main mechanism to prevent spread of infection
6.1.3. Damage and Clinical Manifestations
- Can cause mucous membrane infectcions, cutaneous candidiasis, disseminated candidiasis, endocarditis, cystitis, or peritonitis
6.1.4. Identification and Diagnosis
- Microscopic exam reveals budding yeast cells, pseudohyphae and hyphal elements
- Can be cultured from blood in disseminated infection
6.1.5. Treatment
- Amphotericin-B or fluconazole
6.2. Cryptococcus neoformans
- Encapsulated yeast present in the environment
- Found only in the yeast form
- AIDS is the predisposing factor
6.2.1. Encounter
- Found in pigeon droppings and inhaled into lungs
6.2.2. Spread
- After causing asymptomatic infection in the lungs, the yeast can spread through blood to the brain
- Brain abscesses cause damage by displacement, not inflammation
6.2.3. Damage and Clinical Manifestations
- Can cause pneumonia, skin lesions, or bone lesions like other fungi
- Most common presentation is meningitis
- Symptoms include: headache, lethargy, coma, personality changes, memory loss, cranial nerve deficits
6.2.4. Identification and Diagnosis
- Cerebral spinal fluid stained with India ink
- Cryptococcal antigen test
6.2.5. Treatment
- Amphotericin-B and flucytosine
6.3. Aspergillus fumigatus
6.3.1. Encounter
- Found in air, soil, and moldy vegetation
- Not part of normal human flora
- Initially invade lung or paranasal sinuses
6.3.2. Spread
- Invasive infection can spread to the brain, bone, skin, liver, and breast
6.3.3. Damage and Clinical Manifestations
- Lung infection causes consolidation, lobar pneumonia, and lung cavities
- Can form fungus balls that occlude bronchi
- Angioinvasive that can cause ischemia and necrosis
- Allergic bronchopulmonary aspergillosis from Type I hypersensitivity
6.3.4. Virulence Factors
- Toxic metabolic products called aflatoxin that are hepatotoxic and carcinogenic
6.3.5. Identification and Diagnosis
- X-ray or CT scan can reveal aspergillomas
- Sputum exam or blood culture show characteristic branching hyphae
6.3.6. Treatment
- Allergic reactions treated with corticosteroids
- Fungus balls must be surgically removed
- Invasive disease treated with Amphotericin-B
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