MGY277H1 Lecture Notes - Lecture 4: Prenatal Development, Cestoda, Signify

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Unit 4  Eukaryotic Microbes
Fungi
Fungal pathogens are particularly problematic for people who are
immunocompromised” individuals who have weak immune system due to AIDS,
immune-suppressive drugs, or other infections.
Opportuistic Vs. Primary Pathogens
Opportunistic  only ccasue disease in immunocompromised individuals
Primary  can also cause disease in otherwise healthy individuals
All eukaryotic organisms fall into domain [Eucarya]range from plants to animals
to microscopic members (Animals , Plants, Fungi, Protista)
Fungus
All fungi are eukaryotes
Cell wall contains chitin (same molecule that forms
the exoskeleton of insects) Vs. bacteira cell wall
made of peptidoglycan
Cell membrane composed of ergosterol vs. animal
cell membrane compsoed of cholesterol (Ergosterol biosynthesis is a major
anti-fungal drug target)
Fungal Morphogenesis
Different species of fungi can exist in multiple forms
oSingle celles-yeast
oMulti-celled filaments (hyphae or pseudohyphae)
oSpores
Fungal spores everywhere on earth, up to altitudes of more than 7 miles (air
may contain >10,000cells/m3)
With each breath you take, it is estimated that you breath in 5 fungal spores
Fungal Disease
Fungi can cause disease in 3 main ways
1. Allergic or asthmatic reation to either the fungus or its spores
2. Grow ON or IN the human body mycosis (superficial or systematic)
3. Fungus produce toxic that causes illness after ingestion
Fungal Species
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1. Cryptococcal Meningoencephalits
2. Candidiasis
3. Histoplasmosis
4. Pneumocystis phenumonia
Cryptococcal Meningoencephalits
Worldwide distribution in soil, vegetation contaminated with bird droppings
Entry via inhalation of spores
Encapsulated yeast cells spread through the bloodstream after
inhalation to disparate part of the body (often infect meninges and
adjacent brain tissue
Case fatality rate is 5-25%)
Symptomatic infection sometimes the first indication of AIDS
2 major form that cause human disease
a. Cryptococcus neoformans
An opportunistic pathogen mostly infect immunocompromised people
Spherical yeast ~3-20 um diamters
Surrounded by thick capsule that resists immune response
b. Cryptococcus gattii
A primary pathogen that cause disease in healthy individuals (an
emerging threat to health in the pacific northwest of the US and Western
Canada)
Several porpoises washed up dead in BC in 2000 (all were positive for
C.gattii)
Candidiasis (Candida albicans)
Normally lives as part of our microbiota
Disruption of the microbiota due to underlying health issues or the
use of certain medications can perturb the balance
These fungi cause disease by invading deep layers of the skin and
subcutaneous tissue
Key aspect of C/albicans pathogenesis is that it its dependent on the fundis
ability to switch between yeast and filamentous forms (to cause
different diseases)
oIf they are unable to switch, they are less invasive
Histoplasmosis (Histoplasma capsulatum)
Found in soil contaminated by bird or bat dropping
Severe form of the disease resemble the symptoms of tuberculosis
Usually indicates that the patient has an underlying immunodeficiency such
as threat cause by AIDS
Similarities to TB extend to the cellular mechanisms of disease
oAfter inhalation of Spores. H.Capsulatum grows inside macrophages
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