Tropism and Injury

Question 1

What are the types of Vertical Transmission?

Answer 1

The types of vertical transmission are placental fetal transmission (mother becomes infected while pregnant), transmission during birth and postnatal transmission through maternal milk.

Question 2

How does the skin protect against microbes?

Answer 2

The skin protects against microbes by providing a low pH, fatty acids, a dense keratinized outer layer. Therefore, microorganisms must break the skin.

Question 3

How does the gastrointestinal tract protect against microbial growth?

Answer 3

Undergoes acidic gastric secretions and peristalsis, has a viscous mucous lining, pancreatic enzymes, bile, defensins and has normal microbiota (takes up space and has a biological defense).

Question 4

How do microbes enter the gastrointestinal tract?

Answer 4

1. When local defenses are weak
   - Antibiotics
   - Immunocompromised
2. Organisms can overcome defenses
   - Some bacterial are resistant to acidity
   - Non-enveloped viruses have coats that protect them from bile

Question 5

How does the urogenital tract protect against microbes?

Answer 5

The urogenital tract protects against microbes by regularly flushing of sterile urine. The vagina has a low pH.

Question 6

How do microbes still enter the urogenital tract?

Answer 6

• Pathogens adhere to the urinary epithelium or via the urethra
• Or adhere to vaginal/ cervical mucosa
• Usually with immunocompromisation or with use of antibiotics

Question 7

How does the respiratory tract clear microorganisms?

Answer 7

Large particles are removed by the mucociliary elevator and small particles are removed by alveolar macrophages.

Question 8

How do microbes disseminate (spread)?

Answer 8

Microbes can multiply locally at the site of infection or disseminate throughout the body via the bloodstream, lymph system or nerves. Can break barriers by secreting lytic enzymes.

Question 9

What is tissue tropism?

Answer 9

Tissue tropism is the ability of a pathogen to infect a certain type of cell, organ or tissue.

Question 10

What dictates tissue tropism?

Answer 10

Tissue tropism is determined by…
- Receptors – Does the host’s cell have a receptor for the pathogen to bind to and effect?

• Anatomical barriers/ host defenses – Can the pathogen actually overcome the host barriers and infect the host?
• Transcription factors – Bind to DNA so that it can convert to mRNA for replication to occur
• Environmental factors – What temperature, pH, etc. can the pathogen handle?

Question 11

How can microorganisms cause disease?

Answer 11

Microorganisms can cause disease directly through contact and replication. Or they can cause disease indirectly through the release of enzymes or toxins.

Question 12

What is an endotoxin?

Answer 12

An endotoxin is a toxin produced by and associated with a microorganism. Can activate the inflammatory response and cause shock.

Question 13

What are exotoxins?

Answer 13

Exotoxins are secreted by the microorganism. Can act at tissue sites that aren’t affected by the pathogen growth. They include; enzymes, neurotoxins and superantigens.

Question 14

What is a neurotoxin?

Answer 14

A neurotoxin is an exotoxin that inhibits the release of neurotransmitters. They don’t kill the cell, but have the capacity to kill the host.

Question 15

What are superantigens?

Answer 15

Superantigens are exotoxins that bind to the conserved regions of t-cell receptors. This causes stimulation of alot of t-cells, leading to lymphocyte proliferation, release of cytokines and shock.

Question 16

What injuries can be caused by the host’s immune response?

Answer 16

The host’s immune response to a microorganism leads to the activation of…

• Cellular immune response
• Humoral immune response
• Chronic inflammation
• i.e. Spanish flu

Question 17

What are the ways microorganisms can evade the immune system?

Answer 17

Microorganisms can evade the immune system by…

• Growing in places they cannot be detected
• Changing their antigenic variation
• Inhibiting the innate immune response by preventing phagocytosis

Question 18

What determines if bacteria can cause injury?

Answer 18

• Bacteria’s ability to adhere to host cells
• Ability to invade cells/ tissues
• Virulence genes

Question 19

What is quorum sensing?

Answer 19

Quorum sensing is when bacteria coordinates gene expression in a large population. Example of this is forming biofilms to prevent antimicrobial drugs or immune response.

Question 20

What is pathogenicity?

Answer 20

The ability of a microorganism to cause disease

Question 21

What is pathogenicity dependent on?

Answer 21

Pathogenicity depends on virulence factors.
Examples of virulence factors:
- Ability to adhere to host
- Production of toxins
- Speed of replication
- Degree of tissue damage

Question 22

What are the 4 Koch’s postulates?

Answer 22

1. Microorganism must be present in all sick individuals, but not present in the healthy
2. Microorganism must be able to grow in pure culture
3. Must then cause disease if presented to someone
4. Microorganism is once again isolated from the individual