Bacteria

Question 1

What are the key components of bacteria?

Answer 1

Cytoplasmic membrane, cytoplasmic matrix, ribosomes, genome, cell wall

Question 2

What are the components of the bacterial genome?

Answer 2

Nucleoid comprising one closed circle of dsDNA

Plasmids of DNA that replicate independently of the chromosome

Question 3

What is the difference between the core genome and the accessory genome of bacteria?

Answer 3

The core genome comprises of the genes that every member of a bacterial species must have. They are thought to be essential.
The accessory genome comprises genes that can be found within the species, but is not present in all strains.

Question 4

What cell walls can be found in bacteria?

Answer 4

Gram +ve, Gram -ve, acid fast

Question 5

Describe the Gram-positive cell wall

Answer 5

One thick layer of peptidoglycan surrounds the plasma membrane. In this cell wall are embedded molecules such as teichoic acid

Question 6

Describe the Gram-negative cell wall

Answer 6

A thin layer of surrounds the plasma membrane. It, in turn, is surrounded by a lipid outer layer which is stabilised by lipopolysaccharide (LPS)

Question 7

Describe the acid fast cell wall

Answer 7

Seen in mycobacteria, it is a thick, waxy wall lacking in the usual PAMPs, making it difficult for the immune system to fight effectively. The wall also makes the bacteria very resistant to harsh conditions, while limiting the rate of nutrient uptake of the bacteria.

Question 8

What is the function of pili and fimbriae?

Answer 8

Adhesion of bacteria to each other and to host cells

Question 9

What do capsules of bacteria achieve?

Answer 9

They provide protection from dehydration and phagocytosis, and affect virulence

Question 10

Describe endospores

Answer 10

Specialised structures of bacteria that are highly resistant and dormant, able to survive for a very long time until conditions are more favourable for the bacteria.

Question 11

What are 4 characteristics of the genus Clostridium?

Answer 11

Gram +v, rods, anaerobic, spore forming

Question 12

How can bacteria cause disease?

Answer 12

Colonisation, invasion, multiplication, tissue damage

Question 13

How do pathogenic bacteria colonise a host?

Answer 13

They must overcome host defenses and overcome competition from commensal bacteria, often by adhering to epithelial walls via fimbriae or adhesins in outer membranes.

Question 14

How can bacteria invade a host?

Answer 14

They must get back the epithelium. Some bacteria do this by moving between cell, but most move through cells using pathogen-mediated endocytosis. This is initiated by invasins on the bacterial cell surface.

Question 15

How are bacteria able to overcome host defences?

Answer 15

Evading phagocytosis, or resisting killing

Question 16

How can bacteria evade phagocytosis?

Answer 16

Some bacteria use leukodicins to break down white blood cells. Others suppress the inflammatory response. The most common method is to use anti phagocytic structures such as capsules.

Question 17

How can bacterial capsules help evade phagocytosis?

Answer 17

The high negative charge provide electrostatic repulsion that makes it more difficult for host cells to surround and ingest capsular bacteria
The capsule can mimic host components, making the capsule non-antigenic
The capsule masks underlying PAMPs that would otherwise be detected by host PRRs

Question 18

How can bacteria resist killing?

Answer 18

Inhibiting the respiratory burst
Preventing phagolysosome formation
Escaping the phagocytic vacuole
Just being too hard to kill (eg. mycobacterium tuberculosis)