Introduction to microbial infection

Question 1

What are Koch’s postulates

Answer 1

1. The suspected pathogen must be present in all cases of the disease and absent from healthy animals
2. The suspected pathogen must be grown in pure culture
3. Cells from a pure culture of the suspected pathogen must cause disease in a healthy animal
4. The suspected pathogen must be reisolated and shown to be the same as the original

Question 2

Limitations to Koch’s postulates

Answer 2

1. Difficult to grow
2. Obligate parasites - cannot grow alone
3. Restricted host range
4. Subclinical (silent) infections

Question 3

What is an infection

Answer 3

A disease caused by a pathogen

Question 3

What is a pathogen

Answer 3

A microorganism that can invade the body and cause disease

Question 4

What are physical barriers

Answer 4

Skin and mucous

Question 5

What are chemical barriers

Answer 5

Lysozyme and sebum

Question 6

What are phagocytic cells

Answer 6

Macrophages, monocytes, neutrophils, dendritic cells and mast cells

Question 7

What is a commensal

Answer 7

A microorganism which forms part of the normal host microbiota

Question 8

What is a pathogen

Answer 8

An organism/agent that causes disease

Question 9

What is a pathogenesis

Answer 9

The development of disease

Question 10

What is pathogenicity

Answer 10

The ability to cause disease

Question 11

What is virulence

Answer 11

A pathogen’s power to cause severe disease

Question 12

What are the factors affecting pathogenicity and virulence

Answer 12

• Number of infecting organisms
• Route of entry
• Immune system
• Intracellular growth and replication
• Virulence factors

Question 13

What is an obligate pathogen

Answer 13

Almost always associated with disease

Question 14

What is an opportunistic pathogen

Answer 14

They do not always cause disease but if given a chance can

Question 15

What are the steps of infection

Answer 15

• Recognition
• Attachment and entry
• Multiplication
• Evasion of host defence
• Shedding and damage

Question 16

How can infection be established

Answer 16

1. Microbes with specific mechanisms for attachment and penetration of host’s body surfaces
2. Microbes introduced into host by biting arthropods
3. Microbes introduced into host via skin wounds or animal bites
4. Microbes able to infect only when host defences are impaired

Question 17

What is endogenous infection

Answer 17

Disease arising from a pathogen already present in the body but previously asymptomatic

Question 18

What is exogenous infection

Answer 18

Disease arising from a pathogen not normally present in the body and comes from the environment

Question 19

What is tissue tropism

Answer 19

Affinity for a specific tissue. Defines the cells and tissues of a host which support the growth of a particular microbe

Question 20

What 3 factors influence transmission

Answer 20

• The no. of microorganisms shed
• The number of microorganisms required to infect a fresh host
• The microorganisms stability in the environment

Question 21

What is fomite transmission

Answer 21

Transmission via inanimate objects

Question 22

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