Introduction to Microbial Infection

Question 1

What are Koch’s postulates?

Answer 1

Bacteria must be present in every case of the disease

The bacteria must be isolated from the host with the disease and grown in pure culture

The specific disease must be reproduced when a pure culture of the bacteria is inoculated into a healthy susceptible host

The bacteria must be recoverable from the experimentally infected host

Question 2

What does the innate immune system contain?

Answer 2

Normal microbiota

Physical barriers

Chemical barriers

Phagocytic cells

Question 3

How does normal microbiota defend?

Answer 3

Competes with pathogens for colonisation sites

Produce antibiotic substances supressing growth of competing organisms

May produce toxic metabolic products to inhibit other micro-organisms

Alter pH

Question 4

What is normal microbiota suppressed by?

Answer 4

Antibiotics

Question 5

What do lactobacilli do?

Answer 5

Conversion of carbohydrates to acidic products

Question 6

Where is lactobacilli found?

Answer 6

Vagina

Question 7

What are some physical barriers?

Answer 7

Skin

Mucomuciliary clearance

Flushing

Peristalsis

Question 8

How does the skin act as a physical barrier?

Answer 8

Secretes sebum and fatty acids to inhibit growth

Question 9

What is mucomuciliary clearance?

Answer 9

Particles settle on sticky mucus of respiratory epithelium

Debris transported by cilia to oropharynx where it is swallowed

Question 10

What are some chemical barriers?

Answer 10

Mucus

Antimicrobial proteins

Gastric acid

Plasma proteins

Question 11

Example of anitmicrbial proteins

Answer 11

Lysozyme

Lactoferrin

Defensins

Question 12

Example of plasma proteins

Answer 12

Complement

C-reactive proteins

Mannose-binding lectin

Transferrin

Question 13

What is the function of lysozyme?

Answer 13

Catalyses the destruction of the cell walls of certain bacteria

Question 14

What is the function of lactoferrin?

Answer 14

Restricts iron availability to bacteria

Question 15

Example of phagocytic cells

Answer 15

Macrophages

Neutrophils

Monocytes

Dendritic cells

Mast cells

Question 16

What are the ways an infection process can begin?

Answer 16

Invading host tissues

Exerting effects from mucosal surfaces

Question 17

What is the definition of commensal?

Answer 17

A micro-organism which forms part of the normal host microbiota

Question 18

What is a pathogen?

Answer 18

A micro-organism capable of causing an infection

Question 19

What is pathogenicity?

Answer 19

The capacity to cause disease

Question 20

What is virulence?

Answer 20

Measure of the capacity to cause disease

Question 21

What is an obligate pathogen?

Answer 21

Almost always associated with disease

HIV

Question 22

What is a conditional pathogen/

Answer 22

May cause disease if certain conditions are met

e.g Bacteroides fragilis

Staphylococcus aureus

Question 23

What is an opportunistic pathogen?

Answer 23

Usually only infections immunocompromised patients

e.g Pneumocystis jiroveci

Question 24

What are the 6 steps of infection?

Answer 24

Recognition

Attachment and entry

Multiplication

Evasion of host defences

Shedding

Damage

Question 25

How can infections be established in healthy hosts?

Answer 25

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

Question 26

What is tissue tropism?

Answer 26

The affinity of a pathogen to a specific tissue

Question 27

What can affect tissue tropism?

Answer 27

Cell receptors Transcription factors Local temperature Physical Barriers pH

Question 28

What tissues does influenza have a high tropism for?

Answer 28

Cilia and microvilli on tracheal epithelium

Question 29

What tissues does vibrio cholerae have a high tropism for?

Answer 29

Intestinal epithelium

Question 30

What tissues does helicobacter pylori have a high tropism for?

Answer 30

Gastric mucosa

Question 31

What are virulence factors?

Answer 31

The factors which allow a bacteria to cause a disease

Question 32

What are the virulence factors?

Answer 32

Toxin secretion Antibiotic resistance Pilus formation Capsule Ion transport systems Adhesion factors Enzymes- proteases, DNAses, lipases

Question 33

What are the two bacterial toxins?

Answer 33

Endotoxins Exotoxins

Question 34

Describe endotoxins

Answer 34

Low toxicity Part of the cell wall of gram negative bacteria Lipopolysaccharide Low specificity

Question 35

Describe exotoxins?

Answer 35

Highly toxic Secreted from bacterial cells Produced by both gram positive and gram negative bacteria Can be converted into toxoids for vaccine use

Question 36

Example of exotoxins

Answer 36

Tetanus toxin Cholera toxin Botulinum toxin

Question 37

What are some important examples of antibiotics?

Answer 37

Meticillin-resistant Staphylococcus aureus (MRSA) Vancomycin-resistant Staphylococcus aureus (VRSA) HIV Malaria

Question 38

What is transmission dependent on?

Answer 38

Number of micro-organisms shed Number of micro-organisms required to infect a fresh host Micro-organism's stability in the environment