Mechanisms of bacterial infection

Question 1

Van Leuwenhoek

Answer 1

First described bacteria as animacules by looking at samples taken from his teeth under a microscope

Question 2

Pasteur

Answer 2

Pasteurization (generation of bacteria), vaccine for anthrax

Question 3

Koch

Answer 3

Created Kochs Postulates in order to identify bacteria. Discovered major bacteria like TB

Question 4

Ehrlich

Answer 4

Introduced first antibiotic in 1910. Arsenic-based against Syphillis

Question 5

Wacksman

Answer 5

Between 1940-1960 discovered most antibiotics used now.

Question 6

Rise of Cellular Microbiology

Answer 6

In 70s/80s as antibiotic resistance went on rise. Bacteriology became important field once again

Question 7

Phylotype

Answer 7

Study of bacteria, see if two species are related based on arbitrarily chosen level of similarity of gene marker.

Normally 97% similarity required. Most common gene marker is rRNA sequence.

Question 8

Phylotype aka

Answer 8

Operational Taxonomic Units

Question 9

Human bacterial diseases subdivide into 3 categories

Answer 9

Caused by

external environment

bacteria found in microflora

changes in host response to microbiota

Question 10

Virulence

Answer 10

Relationship between organism’s virulence factors and ability to cause disease

Question 11

Measuring virulence

Answer 11

Quantitively by

LD50

• lethal dose
• number of bacteria needed to cause death in 50% of population

IF50
- infectious dose

Question 12

Steps of infection by exogenous pathogen

Answer 12

1. Bind to host via adhesins
2. Invade via invasin
3. compete for nutrients
4. grow to form biofilm and reach quorum sensing
5. kill cells or take over their function to spread
6. evade innate and adaptive immune system
7. leave host and infect next one

Question 13

how is iron found in the body

Answer 13

bound to proteins such as lactoferrin or transferrin

free-floating

Question 14

surface virulence factors of bacteria

Answer 14

Flagella - long distance adhesin 
Pili and fimbriae - shorter and extend domain 
Bacterial capsule 
S-layer proteins 
Short fibrils 

All these are examples of adhesins proteins

Question 15

How to bacteria invade host?

Answer 15

Two mechanisms:

1. Through gaps between epithelial cells
2. Crossing though basement membrane

Question 16

Role of invasins

Answer 16

Recognise surface carbohydrates on cells and cleaves proteins into peptides to allow invasion. Proteases.

Question 17

How does bacteria take up iron

Answer 17

Free floating iron via high affinity siderophores

Protein bound iron by proteolysis of protein component

Question 18

Role of protein toxins

Answer 18

Two roles:

Kill cells
Communication between the cells and bacteria. Bacteria take advantages of intracellular communication without the host cell being aware of what is happening.

Question 19

Bacterial mechanisms by which they evade the immune system

Answer 19

Inhibit complement activation and activity
Developed proteins that bind to immunoglobulins
Developed proteins that degrade immunoglobulins
Developed superantigens inhibiting B cell function by causing massive non-specific activation of B and T cells which leads to wasted effort
Antigenic variation
Inhibits phagocyte killing by developing capsule or via intracellular inhibition
Developed superantigens that kill or inactivate large numbers of T cells
Developed bacterial proteases that degrade cytokines and antimicrobial peptides
Biofilm formation

Question 20

Role of biofilm

Answer 20

Biofilm is formed by bacteria surrounded by matrix. this matrix allows the bacteria to avoid contact from the immune cells and complement system (prevents opsonization)

Question 21

What is quorum sensing?

Answer 21

Way in which the bacteria communicate.

Produce autoinducers - let bacteria sense the population density.

When there are few cells in the area - little autoinducers made will diffuse into the environment and the levels of autoinducers that travel into the cell will remain low.

When more bacteria are present - autoinducer concentration will increase as more bacteria are producing them.

When autoinducer concentration gets high enough indicating a critical density of bacteria, autoinducers will bind and activate receptor proteins inside the cells

This protein acts as a transcription factor

Question 22

What type of proteins are adhesins?

Answer 22

High affinity proteins