4.2 Host-Microbe Interactions Part 2

Pathogenicity

The ability of a microbe to cause disease

What does it mean that pathogenicity is a binary state?

A microbe can either potentially cause a disease or it can't.

Virulence

The degree or extent to which a pathogen causes disease

What does virulence depend on?

Both the physiology of the microbe and the physiology of the host's interactions with it.

What is an example of varying virulence?

1918 pandemic influenza A

In which groups are flu infections typically more virulent?

Groups with immature or suppressed immunity, such as the elderly, children under 5, and pregnant/postpartum individuals.

During the 1918 pandemic, which demographic was most affected by the influenza A virus?

Young and middle-aged people who are immunocompetent.

What does immunocompetence mean?

The ability to mount a full and effective immune response.

What severe immune reaction was developed by immunocompetent people during the 1918 pandemic?

Cytokine storm.

What is cytokine storm?

An immune reaction so potent that it damages organs and can lead to sepsis and death.

What is the infectious dose (ID50)?

The infectious dose is the number of cells or viruses needed to infect half of the people who are exposed to them.

What does a lower ID50 indicate about a pathogen?

A lower ID50 indicates that the pathogen is more virulent.

What is the lethal dose (LD50)?

The lethal dose is the amount of a toxin required to kill half of hosts exposed to it if not treated.

What does a lower LD50 indicate about a toxin?

A lower LD50 indicates that the toxin is more potent.

What are Exotoxins?

Toxins made in the microbial cell and secreted ino environment

What are endotoxins?

Toxins that are typically part of the cell's structures and released when the cell dies (typically by antibiotic treatment or immune response).

What molecule do Gram-negative bacteria have in their cell wall?

Lipopolysaccharide (LPS)

What reaction does LPS trigger in the body?

A powerful body-wide inflammatory reaction

What symptoms can low levels of endotoxins cause?

Fever, chills, and hypotension (low blood pressure)

What can high levels of endotoxins lead to?

Sepsis, which can damage organs and cause organ failure

What is an example of a condition that can lead to high endotoxin levels?

Appendicitis

What happens when the appendix ruptures in relation to endotoxins?

Gram-negative bacteria leak into the abdomen, causing the immune system to react and release endotoxins.

What can happen if high levels of endotoxins are not caught in time?

It can cause sepsis.

What do Type 1 exotoxins bind to?

Receptors on the cells of their hosts

What is the effect of Type 1 exotoxins binding to receptors?

They amplify signals inside the cell that can alter cell physiology or lead to cell death

What immune cells can be hyperactivated by Type 1 exotoxins?

B-cells or T-cells

What are examples of a Type 1 exotoxin?

E. coli enterotoxin and S. aureus enterotoxin

What is an enterotoxin?

A toxin that targets the intestines

When is E. coli enterotoxin produced?

During an infection or during growth of the bacteria in food

What happens when E. coli enterotoxin is consumed?

It binds to intestinal cells and causes them to leak salts and water

What are the symptoms caused by E. coli enterotoxin?

Diarrhea, abdominal pain, and cramping

What type of toxin is Staphylococcus aureus enterotoxin?

It is a T-cell superantigen.

What is a superantigen?

A toxin that hyperactivates adaptive immune cells.

What do superantigens do to the interaction between MHC and T-cell receptors?

They bind to and hyperstabilize the interaction.

What is the result of the massive cytotoxic T-cell response caused by superantigens?

It results in food poisoning by killing the cells of the lining of the digestive tract.

What happens to fluids and salts due to the damage caused by Staphylococcus aureus enterotoxin?

They leak through the damaged lining, causing diarrhea.

What do Type 2 exotoxins do to host cell membranes?

They break open holes in the membrane of host cells.

What can type 2 toxins cause in cells?

Cytoplasm leaking into tissues, inflammatory reaction, cell death

What is an example of a Type 2 exotoxin?

Hemolysin

What does a hemolysin do?

It destroys the membrane of red blood cells (RBCs).

How do hemolysins affect host cells?

They punch holes into the host cell's membrane, causing water to rush in by osmosis and burst the cell.

How is hemolysis detected?

It is detectable on cultures with sheep's blood and is used to classify pathogenic bacteria.

What are Type 3 exotoxins also called?

A-B toxins

What is the function of the binding portion of Type 3 exotoxins?

It binds to a receptor to enter the cell

What does the active portion of Type 3 exotoxins do?

It enters the cell and has a toxic effect.

Type 3 exotoxins examples

Pertussis, Botulinum, and Tetanus toxins

What is pertussis?

Pertussis is an infection of the lower respiratory tract and lungs.

What is the most serious toxin produced by pertussis?

The most serious toxin produced by pertussis is pertussis toxin.

What does pertussis toxin destroy?

Pertussis toxin destroys the ciliated epithelial cells of the lung.

What are the effects of pertussis toxin on the lungs?

It leads to the build-up of mucus and causes severe irritation of the lungs.

What symptom is caused by the combination of irritation and mucus in pertussis?

The combination leads to the signature whooping cough symptom.

What type of nerve cells does Botox primarily affect?

Alpha motor neurons which cause muscle contraction

What neurotransmitter's release is blocked by Botox?

Acetylcholine

What condition is caused by the effects of Botox on muscles?

Flaccid paralysis where the muscles are paralyzed because they cannot contract.

What does tetanus toxin block?

The release of the neurotransmitter glycine.

What type of paralysis is caused by blocking glycine in tetanus?

Spastic paralysis.

Why is tetanus often called lockjaw?

Because spastic paralysis typically affects the muscles of the face and jaw first.

What are fimbriae?

Adhesion structures made of protein that are thin and hairlike.

What are adhesins?

Proteins located on the very end of fimbriae that allow bacteria to attach to specific proteins on specific kinds of cells.

What are slime layers?

Adhesion structures made of densely packed and organized sugars.

How do slime layers appear under a microscope?

They usually appear sharp due to their organization.

What is a characteristic feature of cells with slime layers?

They have a white border around the cells.

Do slime layers use adhesins to stick?

No, they rely on the chemical stickiness of concentrated sugars.