Microorganisms and their properties

Question 1

List in size order, smallest to largest, the microorgansims that can cause infection.

Answer 1

Prions
Viruses
Bacteria (prokaryote)
Fungi (eukaroyte)
Parasites (eukaryote)

Question 2

What is a prion?

Answer 2

Infectious particles of mutant proteins that induce misfolding of host proteins.

Question 3

Where are normal human prion proteins located?

Answer 3

Within neural tissue and tonsils.

Question 4

How are these normal prion proteins affected?

Answer 4

PrPc converted to mutant Prscrapie that fold to form amyloid fibres that deposit in the brain, causing progressive neurodegenerative disease. Loss of motor control and disinhibition.
PrBSE = mad cow disease causing lesions and vacuoles in the brain

Question 5

How are prions transmitted?

Answer 5

Resistant to disinfectants and heat. Usually transmitted from animals through meat which becomes mutant when encounters the PrPsc variant.

Question 6

What is a virus?

Answer 6

An intracellular obligate parasite. It is DNA or RNA within a capsid and in some cases an envelope.

Question 7

Why does a virus require a host?

Answer 7

To replicate within the host using its apparatus for the production of new virus proteins. RNA viruses have the ability to integrate into the genetic material.

Question 8

What can a virus cause?

Answer 8

Degeneration, cell lysis, cell fusion and synyctia formation, cell proliferation, latency

Question 9

What is bacteria?

Answer 9

Can be found externally to a host. Most is beneficial until it enters the wrong environment.

Question 10

What is an obligate, opportunistic and commensals bacteria?

Answer 10

Obligate = Always pathogenic e.g. TB, salmonella
Opportunistic = Can be pathogenic 
Commensals = Never pathogenic

Question 11

What is the structure of a bacteria?

Answer 11

A prokaryote with no membrane bound organelles. Have a rigid cell wall of peptidoglycans.

Question 12

What type of cell walls can a bacteria have?

Answer 12

Gram -ve wall = a DOUBLE membrane with a THIN layer of peptidoglycans e.g. Ecoli
Gram +ve wall = a SINGLE membrane with a THICK layer of peptidoglycans e.g. staphylococci, streptococci

Question 13

How can gram -ve be distinguished from gram +ve?

Answer 13

-ve stains PINK

+ve stains PURPLE

Question 14

How does bacteria cause damage in the host?

Answer 14

Produces exotoxins or causes direct tissue damage through invasion.

Question 15

What are symptoms?

Answer 15

The response of the immune system to a pathogen

Question 16

What is the bacterial cell wall composed of?

Answer 16

Peptidoglycans to form the shape and structure.
Lipoteichoic acid is an immune irritant of gram +ve that causes septic shock.
Lipopolysaccharide/LPS is an endotoxin of gram -ve that is an immune stimulator that causes sepsis.
Lipid A is found on LPS in gram -ve that causes toxic shock.

Question 17

Which part of bacteria mutates when under pressure of treatment?

Answer 17

The polysaccharides in LPS act as O antigens that mutate

Question 18

What features can a bacteria have?

Answer 18

Flagellum - For chemotaxis movement
Pilli/Fimbrae - Allow attachment to host cells. Sex pilli allow transfer of plasmid DNA between bacteria = spread of antibiotic resistance.
Capsule - Protects from phagocytosis

Question 19

Why are infants more susceptible to infections to sugary microbes?

Answer 19

Response to sugary microbes isn’t fully developed and the capsule is preventing phagocytosis.

Question 20

What are fungi?

Answer 20

A single or multicellular eukaryote that contains membrane bound organelles surrounded by a cell wall of polysaccharide chitin and glucans.

Question 21

How do most fungi grow?

Answer 21

As Hyphae - cyclindrical tubes that interconnect to form mycelium. Can produce fruiting bodies or spores.

Question 22

What is the cause of thrush?

Answer 22

Candida albicans in moist, slightly acidic environments.

Question 23

Where are fungi likely to infect?

Answer 23

Skin and respiratory tract but can cause systemic infection in immunocompromised Pts.