Lecture 3: Bacterial Pathogenesis

Question 1

What are the types of Pathogenic Microbes?

Answer 1

• Bacteria
• Fungi (yeasts and molds)
• Parasites
• Viruses
• Sub-viral agents (eg. prions)

Question 2

What is Koch’s Postulates?

Answer 2

• Scientific basis for establishing cause and effect relationships between an organism and a disease.

Question 3

What are the benefits of Koch’s Postulates?

Answer 3

• Act as a guide for determining the cause of a disease caused by an unknown infectious agent.

Question 4

What is the First Postulate and exception?

Answer 4

• Microbe must always be associated with the lesions of the disease
Exception: Asymptomatic carriage

Question 5

What is the Second Postulate and exceptions?

Answer 5

• Microbe must be isolated from lesions of disease and in pure culture
Exception: Some pathogen can not be grown in artificial culture and need other microorganisms to grow
Viruses.

Question 6

What is the Third Postulate and exceptions?

Answer 6

• Pure culture of the microbe should produce the disease when inoculated into a human or animal
Exception:
-experimentation can be unethical (humans)
-Not all organisms exposed to an infectious agent will acquire the infection.

Question 7

What is the Fourth Postulate and exceptions?

Answer 7

• Microbe must be re-isolated from the infected human or animal
Exception: problem for organisms that cannot be isolated in artificial culture media.

Question 8

Whats is Koch’s possible Fifth Postulate and exception?

Answer 8

Therapeutic or preventative measures aimed at the microbe should control or eliminate the disease
Exception: There are no known cures for many infections.

Question 9

Define Pathogenicity?

Answer 9

The ability to cause disease.

Question 10

Define infection and cardinal signs?

Answer 10

invasion by pathogenic organisms resulting in a host response, usually inflammation

• Redness
• Swelling
• Pain
• Loss of function - Heat

Question 11

Define Endogenous infection?

Answer 11

Infection by member of the normal flora.

Question 12

Define Exogenous infection?

Answer 12

Infection by an organism that is not a member of the normal flora.

Question 13

Define Local infection?

Answer 13

An infection restricted to a confined area.

Question 14

Define Focal infection?

Answer 14

A localised site of infection from which pathogens and/or their products are disseminated to other parts of the body.

Question 15

Define Systemic infection?

Answer 15

An infection spread throughout the body.

Question 16

Define Primary Infection?

Answer 16

Initial infection caused by one pathogen.

Question 17

Define Secondary Infection?

Answer 17

Infection that follows a primary infection as a complication.

Question 18

Define Latent Infection?

Answer 18

Dormant infection that flares at a later date.

Question 19

Define Acute Infections

Answer 19

Rapid in onset and often more severe.

Question 20

Define Chronic Infection

Answer 20

Slow, progressive infection.

Question 21

Define Disease

Answer 21

– Any deviation from or interruption of the normal structure or function of any body part, organ, or system.

Question 22

Define Infectious Disease?

Answer 22

A disease caused by pathogenic microorganisms that causes significant overt damage to the host.

Question 23

What does infection imply?

Answer 23

 colonisation
 multiplication
 invasion
 persistence
(symptom being inflammation).

Question 24

Define Virulence?

Answer 24

Is the degree of pathogenicity.

Question 25

Pathogen that has a single determinant of virulence?

Answer 25

 Clostridium tetani

Question 26

Example of pathogens that have a large repertoire of virulence factors?

Answer 26

 Staphylococcus aureus

 Streptococcus pyogenes

Question 27

Define ID50 (infectious dose 50)?

Answer 27

Is the number of bacteria necessary to infect 50% of the population of animals exposed to the pathogen.

Question 28

Define LD50 (lethal dose 50)?

Answer 28

Is the number of bacteria necessary to kill 50% of the population of animals exposed to the pathogen.

Question 29

Microbes that rarely form disease?

Answer 29

Commensals.

Question 30

Name and define the different Pathogen types?

Answer 30

Opportunistic pathogens
 Infection by an organism that ordinarily doesn’t cause disease but becomes pathogenic under certain
circumstances (i.e. if an organism gains entry to a sterile site).
Obligate pathogens
-always cause disease in order to be transferred from one host to another and infect the host to survive.
Overt pathogens
-an organism that is ALWAYS regarded as being pathogenic.