17 - Host/Microbe Interactions
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What are the 3 symbiotic relationships between host and microbe?
- Mutualism - Both benefit
- Commensalism - One benefits, other is unharmed
- Parasitism - One benefits at expense of host
How does our normal microbiota play help us?
- Protects us from harmful organisms by covering binding sites, consuming available nutrients and producing toxic compounds, and stimulating our immune systems.
- Acquired at birth.
3 Things that can kill normal microbiota:
- 1. Chemicals/Chemo
- 2. Burns
- 3. Auto-immune Defeciencies
When is the term "infection" used?
- If the colonizing organism has a parasitic relationship with the host.
- An infection that results in disease is termed an "infections disease."
What are signs and symptoms?
- Symptoms - Experienced by patient, ie pain/nausea
- Signs - Can be observed through examination, ie Rash, Swelling, Pus
What are primary and secondary infections?
- Primary - Initial infection
- Secondary - Additional infections resulting from the primary infection
What is pathogenicity?
The ability of a pathogen to produce an infectious disease in an organism.
What is virulence?
- Term referring to a pathogens disease causing ability.
- Highly virulent organisms have a high degree of pathogenicity.
What is an opportunistic pathogen?
Microbes that cause disease when the body's defenses are down.
What is the "infectious dose?"
- Number of organisms required to establish infection
- Diseases with SMALL infectious doses are more easily spread than diseases with HIGH infectious doses because less of the microbe is needed.
What is the course of an infectious disease?
- Incubation - Time between infection and onset of symptoms
- Illness - Signs and symptoms
- Convalescence - Recuperation and recovery; may still be contagious
What are the duration of symptoms?
- Acute - Rapid onset, last a short time
- Chronic - Develop slowly and persist
- Latent - Never completely eliminated, may be reactive
What is a localized infection?
- Limited to a small area.
- Example - Boil
What is a systemic or generalized infection?
- Microbe spreads throughout body
- Example - Measles
What is toxemia?
Toxins circulating in the blood stream
What is viremia?
Viruses cirulating in the blood stream
What is septicemia?
Life-threatening illness caused by infectious agent or its products circulating in the blood
What separates disease and non-disease causing organisms?
Their ability to overcome the body's immune system
What is a "mechanism of pathogenicity?"
- Mechanism used to overcome the body's immune responses
- More than one mechanism is called "Virulence Determinants"
What steps must an organism take to cause disease?
- Adherence - Binding to the hosts cells
- Colonization - Must successfully multiply, compete for nutrients
- Delivery of Effector Molecules - Must be able to deliver colonized cells to host
How do organisms get in to our bodies?
- Penetration of skin - most difficult
- Penetration of mucous membranes - most common
How do bacteria avoid the hosts defenses?
- Hide in a host cell - some can transfer from cell to cell
- Avoid being killed by complement protiens - Gram negative cells more susceptible
- Avoiding antibodies -
How can a bacteria avoid antibodies?
- IgA protease
- Antigenic Variation - alternation of surface antigens
- Mimicking Host Molecules
What are exotoxins?
- Toxins that are leaked or secreted by bacterium
- Among most potent toxins known
- Can act locally or systemically
What are the 3 types of toxins?
- Neurotoxins - damage nervous system
- Enterotoxins - damage intestines/digestive tract
- Cytotoxins - Damage to variety of cells, cause interference with cell function and lysis
What are membrane damaging toxins?
Disrupt the plasma membrane of a cell
What are superantigens?
Antigens that override T-Cell response and cause toxis effects due to massive release of cytokines by helper t-cells.
Which toxin in responsible for Septic Shock?
What are some damaging effects of immune response?
- Drop in blood pressure
What are the mechanisms of viral pathogenesis?
- Binding to host cell/Invasion
- Avoiding immune responses
What are the mechanisms of Eukaryotic Pathogenesis?
- Fungi - Infection begins with inhalation of airborne particles, Spores lodge in lung tissues
- Eukaryotic Parasites - Most live in intestinal tract, or enter body via bite of an arthropod, attach to hosts via specialized receptors, some hide within host cells.
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