Steps of Pathogenesis

What are the 5 Steps of Pathogenesis?

1. Entry - Portals

2. Adhesion

3. Invasion

4. Damage

5. Exit

What are the three portals of entry?

1. Mucous membranes: GI tract through food and water

2. Skin (intact): via hair follicles and sweat ducts

3. Parenteral route: Only accessed when skin is injured, helping microbes deposit directly into tissues

What is Salmonella’s ‘preferred’ portal of entry?

Salmonella needs to be ingested for a disease to occur

What does Virulence mean?

Virulence means how severe a microbe becomes

What is ID₅₀?

ID₅₀ is the number of microbes required to infect 50% of the population. A lower ID₅₀ means greater virulence

What is LD₅₀?

LD₅₀ is the number of microbes required to kill 50% of the population. A lower LD₅₀ means greater virulence

What are Adhesins?

Adhesins are special proteins on pathogens that allow them to attach to specific receptors on host cells

What are some examples of Adhesins?

Some examples of Adhesins include fimbriae and bacterial flagella

What is an example of a biofilm?

Biofilm example: Pseudomonas aeruginosa in lungs

What are the 4 ways microbes evade phagocytosis?

1. Inhibit adherence

2. Escape phagosome

3. Prevent phagosome-lysosome fusion

4. Survive in phagolysosome

What does Surface M protein and bacterial capsule do regarding phagocytosis?

Surface M protein and bacterial capsule inhibit phagocytosis

What are the three exoenzymes?

• Exoenzymes:

  • Coagulase: forms blood clot around bacteria for protection

  • Kinase: digests blood clots formed by the body to spread infection

  • IgA proteases: destroys IgA antibody

What is Antigenic variation?

Antigenic variation is when a pathogen changes its antigens so that antibodies can’t bind to them as effectively

What are some examples of Antigenic variation?

Examples of Antigenic variation: Influenza virus, Neisseria gonorrheae

What do microorganisms secrete to break down host connective tissue and examples of this?

Microorganisms secrete a variety of extracellular enzymes that break down host connective tissue which allow penetration

• Examples: Hyaluronidase, collagenase, nuclease

What does Helicobacter pylori release to neutralize stomach acid?

Helicobacter pylori releases urease to neutralize stomach acid

What are invasins and what do they do?

Invasins are proteins produced by pathogens and they rearrange host cell structure to force the cell to take the pathogen in

What are some examples of Invasins?

Invasins examples: Salmonella, Shigella

What are the three ways bacteria harm their host?

1. Direct damage

2. Competition over nutrients

3. Production of toxins (toxigenicity)

Describe direct damage

Direct damage is when bacteria multiply causing the host cells to be crowded and damaged by pressure

Describe competition over nutrients

Competition over nutrients are when bacteria produce their own proteins called siderophores that bind to iron more than our iron-binding proteins

• They can also produce enzymes that damage our iron-binding proteins such as hemolysins

Describe production of toxins (toxigenicity)

The production of toxins harms us directly because they are poisonous substances produced by microbes

What does Toxemia mean?

Toxemia is the presence of toxins in blood

Exotoxins vs. Endotoxins chart

What are the three Exotoxins?

1. Intracellular A-B exotoxins

2. Membrane-disrupting exotoxins

3. Superantigens

What is Intracellular A-B exotoxins and examples of this?

Intracellular A-B exotoxins: contains an active (A) component and a binding (B) component

• Examples: Tetanus toxin, botulinum toxin, cholera toxin

Describe the mechanisms of botulinum toxin

1. Botulinum toxin blocks the release of acetylcholine, stopping muscle contraction, leading to Botulism paralysis

Describe the mechanisms of tetanus toxin

2. Tetanus toxin prevents the release of glycine and GABA, which prevents the relaxation of muscles, leading to muscle spasms

What do Membrane-disrupting exotoxins do to host cells and examples of this?

Membrane-disrupting exotoxins: leads to the lysis of host cells

• Examples: C. difficile toxins, S. aureus alpha toxin

What do Superantigens do to immune response and examples of this?

Superantigens: provoke a very intense immune response which leads to a sudden release in cytokines

• Examples: toxic shock syndrome toxin produced by S. aureus

When are Endotoxins released?

Endotoxins are released during gram negative bacterial multiplication

What symptoms do Endotoxins lead to?

Endotoxins lead to the same nonspecific symptoms, such as chills, fever, weakness

What is are some examples of diseases caused by endotoxins?

Endotoxin disease examples: Typhoid fever caused by Salmonella typhi, and neisseria meningitis

How do endotoxins cause fever and inflammation?

Endotoxins cause fever and inflammation by producing interleukin-1. Interleukin-1 causes the hypothalamus to produce prostaglandins, bringing the body’s temperature higher resulting in a fever

What does TNF do to blood vessels?

TNF increases the permeability of blood vessels, leading to edema and shock

How do pathogens exit their host?

Pathogens exit their host through the same portals of entry

How do eukaryotic parasites exit?

Eukaryotic parasites can actively exit