Mycology III - Opportunistic Flashcards Preview

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Flashcards in Mycology III - Opportunistic Deck (36):

What are "Opportunists"?

Microbes/pathogens that only cause disease in host when defenses are disturbed (i.e. immunocompromised) or if they migrate from normal tissue to other tissues


Defects that lead to increased susceptibility

Compromised anatomic and physical barriers
Inherited immunodeficiency
Cancer (esp. lymphohematologic malignancies)
Chemotherapy and Radiation Therapy
Extremes of Age
Other Infections


Specific drugs in chemotherapy that increase susceptibility

Cytotoic drugs and radiation targeting proliferating cells (such as lymphocytes and neutrophils)
Steroids (suppress macrophage activity)
Cyclosporin (transplant patients, suppress T-cell activation)


Specific infections that increase susceptibility

Herpes based: Cytomegalovirus (HCMV) and Epstein-Barr virus (EBV)
HIV (Destruction and suppression of CD4+ lymphocytes)


Candida - Morphology

Both yeast and hyphae seen within human host
Intermediate: pseudohyphae or chains of yeast
Cultivate at room temperature and acidic pH
Pseudohyhal form is tissue invasive and grows in physiological conditions
A variety of the forms can be found in a clinical specimen


Candida - Environmental Niche

Commensal part of the normal flora on human skin and mucous membrane
50-80% of normal individuals may have in oropharynx, GI, or vagina w/o disease
Prefers moist skin


Candida - Epidemiology

Candidiasis begins from their own commensals, for newborns from mother's GI or GU tract
Superficial cutaneous and mucosal infections common in normal hosts
75% of women have at least one bout of vulvovaginal candidiasis (uncommon prepuberty)
Most common microbial infection in AIDS, 90% of patients have thrush and 10% have esophagitis


Candida - Virulence determinants

- Can mimic integrin CR3, CR4 on host macrophages
- Mannoproteins similar to integrins for binding to ECM components
- Hwp1: Hyphal wall protein helps mediate binding
Invasive pseudohyphae to infect tissue, yeast at the disease site
Hydrolytic enzymes for destroying host tissue and tissue invasion


Biofilms (Definition, What increases risk for them, Immunological repercussions)

Structured microbial communities that are attached to a surface or encased in ECM
Devices such as stents, implants, catheters increase biofilm proliferation
Biofilm prevents phagocytosis, reservoir for future infection, increased resistance to antifungal therapy


Candida - Infection

Skin, nail and mucosal infection due to compromised local host defenses
Host environmental conditions can favor fungal growth
Sites of surgical procedures, catheters favor candida growth and colonization
Candida spp. are leading cause of neonatal ICU deaths
Severe mucosal infections and invasive and disseminated disease occur in seriously immunocompromised individuals


Candida - Clinical Syndromes

Cutaneous - Dermatitis, onychomycosis, otitis external
Mucosal - Vulvovaginal, oropharyngeal (thrush, white patches in mouth), denture-associated stomatitis, esophageal
Chronic mucocutaneous candidiasis - Mixture of these infections, often reduced T-cell response but good or enhanced humoral response
Invasive/disseminated - Pulmonary, fungemia, endocarditis, urinary tract, meningitis


3 Main Risk factors for invasive candidiasis/candidemia

Central venous catheter
Broad spectrum antibiotics
Surgery (especially if transects gut wall)


Candida - Clinical challenges

Differentiating candida pseudohyphae (no speta) from Aspergillus and other true hyphae in tissue
Azole resistance, esp. non-albicans
Oral candidiasis in asthmatics


Cryptococcus - Morphology

Uninucleate budding yeast with poly saccharide capsule


Cryptopcoccus - Geographic distribution and niches

Worldwide, ubiquitous in soil
Associated with bird guano especially pidgeons but do not cause birds to become ill
Not part of normal human microbial flora


Cryptococcus - Variants and strains

C. neoformans var. grubii - serotype A
C. neoformans var. neoformans - serotype D
C. gattii - serotype B, C


Does cryptococcus have outbreaks?

Not C. neoformans
C. gattii does, example in Pacific NW


Cryptococcus - Epidemiology

Global, particularly bad in sub-Saharan africa: 720,000 cases per year, 65% dying within 3 mos of diagnosis
Life-threatening in 6-12% of AIDS patients
High mortality in developing countries with poor drug availability


Cryptococcus - Virulence

Growth at 37 C
***Capsule - Protects against phagocytosis by hiding fungal cell wall ligands or making yeast too large
Depletion of complement components
Down-regulates immune response, NO synthase, leukocyte migration
Phenoloxidase activity/melanin production protect against oxidation
Mannitol production to scrub free radicals


Cryptococcus - Infection

Exposure - Very common via respiratory and GI
Major route - Desiccated yeast become airborne, inhaled by mammalian host, penetrate small airways
***Location predominately extracellular in host
No necrosis or organ damage till late, little inflammation
Rare in children regardless of HIV


Cryptococcus - Clinical syndromes

Pulmonary - Patients may be asymptomatic or present with cough, fever, pneumonia like symptoms
Meningitis - Oftern first indication of cryptococcal infection, most common and most serious (100% mortality w/o treatment, 12% with)
Skin and Prostate also targets of dissemination


Aspergillus - Morphology

Mold - septate (crosswalls) hyphae (mycelia) + conidia
No yeast form


Aspergillus - Geography and environmental niches

Ubiquitous in environment, decomposing vegetation, household dust, building materials
Airborne exposure common


Aspergillus - Strains that cause infection

***Only a few of the 100+ species
A. fumigatus: 60-70%
A. flavus: 10-20%
A. terreus: 3-12%
A. niger: 0-5%


Aspergillus - Outbreaks

Construction projects and materials in several hospitals


Aspergillus - Virulence

Hydrolytic enzymes (proteases) for tissue destruction
Allergens inducing host response


Aspergillus - Infection

DIsease is uncommon unless compromised adaptive or ***innate*** immunitiy.
Host defense begins with mucous layer and ciliary action in the airway
Macrophages kill conidia, neutrophils kill hyphae
Neutropenic patients are at high risk for invasive aspergillosis
HIV alone often not enough to cause susceptibility


Aspergillus - Clinical Syndromes

Saprophytic colonization of pre-existing body cavities
***Invasive - Inflamation, granulomatous, necrotizing lung diseases. Invade blood vessels and disseminate. Very poor prognosis.
Allergy - Hypersensitivity pneumonitis or Allergic Bronchopulmonary aspergillosis (ABPA). ABPA can lead to fibrotic end-stage lung disease
Mycotoxicosis - Aflatoins are hepatotoxic and carcinogenic


Main Challenge for Aspergillosis

Quick diagnosis


Zygomycosis - Overview

Includes Rhizopus, Mucor, Fusarium
Recently emerged as significant causes of morbidity and mortality in immunocompromised patients


Zygomycosis - Morphology

Molds in environment and in host
Fusarium are septate, others are not


Zygomycosis - Geographic distribution and environmental niches

Ubiquitous, commonly soil, fruit, plants, insects, bread


Zygomycosis - Epidemiology

Worldwide, no biases
Spread in hospitals via AC systems


Zygomycosis - Virulence Determinants

None known


Zygomycosis - Infection

Inhalation, ingestion, or contamination by spores
Rarely disease in immunocomptent, but aggressive in immunocompromised (usually fatal)
In particular target acidotic patients, diabetic
Breakthrough infections in bone marrow transplant


Zygomycosis - Special challenges

Discriminating zygomycosis from common bacterial and fungi infections
Correcting underlying conditions like ketoacidosis