Session 1 Lectures - Introduction to infection

Question 1

What is an infection?

two parts to definition

Answer 1

Invasion of a host’s tissues by micro-organisms AND a disease caused by microbial multiplication, sometimes toxins, and a host response (e.g. inflammatory response)

Question 2

Why might symptoms of disease continue after microorganism killed by antibodies?

Answer 2

Because an inflammatory cascade has started

Question 3

Give the 4 ways a person can be infected by their environment?

Answer 3

1. Food
2. Water
3. Air
4. Surface

Question 4

What is a vector and give an example of one that causes infection?

Answer 4

A living carrier

Example: mosquito carrying malaria

Question 5

What does the term endogenous source of infection mean?

Answer 5

A patients own microbial flora can move elsewhere in the body it is not suppose to be and cause infection

Question 6

What are microbiota?

Answer 6

Microorganisms carried on the skin or mucosal surfaces

Question 7

What is vertical transmission and give an example of this?

Answer 7

An infection passed from mother to child (either before or after birth)
Example: HIV - child often gets infected through breast milk

Question 8

Give two ways in which the risk of passing on HIV from mother to child can be reduced

Answer 8

1. Deliver by caesarean section

2. Mother does not breast feed

Question 9

What are the 5 stages in which microorganisms cause disease?

Answer 9

1. Exposure
2. Adherence
3. Invasion
4. Multiplication
5. Dissemination (spreading)

Question 10

What is adherence?

Answer 10

Adhesin (part of bacterial cell surface) interacts with host cell receptor on cell surface allowing bacteria to attach

Question 11

What are virulence factors and give two examples?

Answer 11

They are the properties of a microorganism that enable it to establish itself on a host and enhance potential to cause disease
Examples: endotoxins and exotoxins

Question 12

What are endotoxins?

Answer 12

An endotoxin is a component of the bacterial wall that causes an inflammatory response in the host

Question 13

What are exotoxins?

Answer 13

They are toxins secreted from the bacteria (also secreted during bacterial lysis)

Question 14

Give 4 types of exotoxins

Answer 14

1. A-B toxins (disrupt cell metabolism)
2. Cytolytic (disrupts plasma membrane)
3. Superantigens (results in large release of cytokines and leads to shock)
4. Enzymes

Question 15

What is the inoculum size of a microorganism?

Answer 15

The amount of the microorganism needed for a person to become infected

Question 16

What are supportive investigations?

Answer 16

Investigations that look at how well the patient is

Question 17

Give 5 types of supportive investigations

Answer 17

1. Full blood count (look at levels of WBCs)
2. C reactive protein (increases during inflammation)
3. Liver and kidney function tests
4. Imaging
5. Histopathology (looking at tissue under microscope)

Question 18

What are specific investigations?

Answer 18

Investigations that look to identify cause of infection

Question 19

Give 4 types of specific investigations

Answer 19

1. Specimen samples e.g. fluid
2. M,C & S (microscopy, culture and antibiotic susceptibility)
3. Antigen detection
4. Nucleic acid detection (looking at DNA or RNA)

Question 20

What are the 3 main approaches for identifying a virus?

Answer 20

1. Antigen detection
2. Antibody detection
3. Detecting viral nucleic acid (DNA or RNA)

Question 21

What is a tercian fever?

Answer 21

A fever that appears every 3 days

Question 22

What are Koch’s postulates? List the 4.

Answer 22

Ways of thinking about demonstrating cause of infectious disease

1. Microorganism must be found in all organisms with disease and not in healthy people
2. Microorganism must be isolated and grown in culture
3. Cultured microorganism should cause disease when inserted into healthy person
4. The microorganism should be isolated from this host and matched to original cause