Lecture 13- Mechanisms of infection

Question 1

What are the steps in infection of bacteria?

Answer 1

Colonise the hist
evade host defences
proliferate
cause damage

Question 2

What are the sources of bacteria for infection?

Answer 2

self, other humans, animals, insects, objects. soil, plants, food, drink, water, air

Question 3

What are the methods of transmission for bacteria?

Answer 3

Touch/Direct Contact, Body Fluids, Aerosols, Eating/Drining, Insect Bites, Wounding

Question 4

What are the risk factors for bacterial colonisation?

Answer 4

Surgery and trauma, increased contact with pathogen, damage/poor function of immune system

Question 5

What are the functions of non-specific adhesions on bacteria?

Answer 5

To give reversible binding as seen in S.Aureus teichoic acids or Alginate capsule of Pseudomonas aeruginosa

Question 6

What are specific adhesions of bacteria?

Answer 6

Gram negative bacteria use Pili, Fimbriae and outer membrane adhesions
Gram positives use MSCRAMMs

Question 7

What are host defences to colonization?

Answer 7

Skin and mucosal barriers, antibacterial secretions, iron restriction the complement system, phagocytes and antibody responses

Question 8

What are the methods through which bacteria can evade the host’s defence systems?

Answer 8

Masking and hiding, mimicry, destruction, misinformation

Question 9

How does masking work?

Answer 9

Capsule proteins mask surface proteins that are recognizable to the immune system as well as antigens or complement proteins that may have bound to the bacteria

Question 10

How is a capsular bacteria made vulnerable to the immune system?

Answer 10

A vaccine will attach a highly immunogenic protein to the capsular polysaccharide to generate an immune vaccine for it

Question 11

What is a mechanism of hiding from the immune system that does not involve a capsule?

Answer 11

intracellular replication as seen by mycobacterium tuberculosis

Question 12

What is an example of molecular mimicry?

Answer 12

S.Aureus binds to a layer of ECM proteins via MSCRAMMS as well as using protein A to bind to Immunoglobulins Fc region ‘handcuffing’ them

Question 13

What is an example of destruction?

Answer 13

Degradation of C3b through factor H
Prevention of fusion of phagosome and release of toxins by Bacillis Anthracis
Destruction of 5a by 5a peptidase 
Blocking of 5a receptors
Toxins such as leukocidin

Question 14

What are the methods of misinformation used to evade host defenses?

Answer 14

Mutation of bacterium result in the new strain not being recognised by the immune system which has developed defensive mechanisms against the initial strain
Bleb decoys as in meningococcus

Question 15

What nutrient do bacteria need to obtain in order to grow in the human body?

Answer 15

Iron

Question 16

What methods can bacteria use to obtain iron?

Answer 16

Sideosphores (iron chelators),
Specific binding proteins
Breaking down of proteins that contain iron (haemolysin)
Adapt to higher iron niche of phagosome
Use cofactors other than iron