Pathogenicity: adhesion, colonisation and toxins

Question 1

What needs to be present for a disease to occur?

Answer 1

a microorganism/ a number of bacteria to need body/ the quality of a persons specific and non-specific body defences

Question 2

What are the 2 categories of virulence factors?

Answer 2

1. virulence factors that promote bacterial colonisation of the host
2. virulence factors that damage the host - ectotoxins and endotoxins

Question 3

What are the 6 virulence factors?

Answer 3

1. adhere to host cells and resist physical removal - stick
2. invade host cells - invade
3. contact host cells - contact
4. resist phagocytosis
5. evade immune defences
6. compete for iron and other nutrient

Question 4

true or false dies the body have an innate ability to remove bacteria?

Answer 4

true

Question 5

What are some of theses defences

Answer 5

• shedding of surface epithelial cells from the skin and mucous membrane - skin shedding
• coughing, sneezing, vomiting, diarrhoea
• body fluids like saliva blood mucous and urine

Question 6

What are pili?

Answer 6

thin protein tubes that come out of the cytoplasmic membrane - almost all gram negative bacteria but not many gram positive bacteria

Question 7

What do pili let the bacteria do?

Answer 7

adhere to reception on target host cell and colonise and resist flushing

Question 8

Structure of a pili

Answer 8

shaft made up of protein pilin
at the end there is an adhesive tip which is a protein called lectin which can bind to glycoprotein to fly-lipid receptors on the host cell

Question 9

can pili switch adhesive tips?

Answer 9

Yes - allows them to collate different cell types and so evade antibodies

Question 10

What are adhesins?

Answer 10

proteins in the cell wall of bacteria that bind to receptor molecules on the surface of host cells
they allow bacteria to adhere imtinamly to the cell

Question 11

What are capsules?

Answer 11

capsular polysaccharide matrix forms a biofilm on host tissue - layers of bacteria adhering to host cells and embedding in a capsular mass

Question 12

What is invasin?

Answer 12

proteins found in the cell wall of various bacteria that allow bacteria to penetrate host cells

Question 13

What can invasins do?

Answer 13

active the host cells cytoskeletal machinery enabling bacterial entry into the cell by phagocytosis - engulfment

Question 14

Why does it help the bacteria to the motile - be able to move

Answer 14

better chance of making contact with mucous memebrane in intestines - they can move through the mucous to place les viscous

Question 15

what do capsule allow bacteria to resist

Answer 15

phagocytic engulfment

Question 16

What does IgG do

Answer 16

stick antigens like bacterial proteins to phagocytes

Question 17

structure of an IgG molecule

Answer 17

tip (Fab) has a shape that fits bacterial antigen

stalk (Fc) bind to receptors on the phagocytes

Question 18

What is C3b?

Answer 18

a protein which binds to bacterial surface proteins and C3b receptors on phagocytes once the coplesmen defence pathways are activated

Question 19

What are C3b and IgG called?

Answer 19

opsonins

Question 20

what are ways that bacteria can resist phagocytic destruction?

Answer 20

they prevent the acidification of the phagosomes which is needed for effective killing of microbes by lysosomal enzymes
- can kill phagocytes by producing exotoxin leukocidin
- more resistance to toxic forms of oxygen and to defensins
- block vesicular transport machinery that enables the phages to fuse with the lysome

Question 21

How can bacterial evade immune defenses?

Answer 21

change surface proteins so that the antibodies no longer fit

Question 22

What does bacteria need to do be pathogenic?

Answer 22

compete successfully with host tissue and normal flora for limited nutrients

Question 23

what are the 2 types of virulence factors

Answer 23

1. ones that promote bacterial colonisation
2. ones that damage the host

Question 24

Structure of A-B toxins

Answer 24

B (binding) component which binds to receipt on surface of susceptible host cell
A (active) component which enters host cells start the ADP-ribosylation of target host cell protein

Question 25

What is ADP-ribosylation?

Answer 25

where NAD is cleaved (split) into nicotinamide and ADPR which attached to host cell target proteins and inactivated them

Question 26

What are the virulence factors that damages the host

Answer 26

1. the ability to produce harmful exotoxins
2. the ability to produce cell wall component that bind to hist cells causing them to synthesis and secrete inflammatory cytokines