Bacterial Pathogenesis and Invasion

Question 1

Which factors inhibit colonisation in the skin?

Answer 1

Dry conditions

Acidic pH (5.5)

Regular loss of outer layer

Antimicrobial substances - fatty acids, lysozyme

Skin associated lymphoid tissue

Presence of commensals (bacteria)

Question 2

Which factors inhibit colonisation in the mucosa?

Answer 2

Mucin production which is removed by cilia or peristalsis

Antimicrobial substances

• lysozyme
• lactoferrin
• anti-microbial peptides

Secretory IgA

Regular outer cell layer turnover

Mucosal associated lymphoid tissue

Presence of commensals

Question 3

Which factors aid colonisation of bacteria in the skin and mucous membranes?

Answer 3

Adhesins

Motility

Secretion of mucin-degrading enzymes

Ability to rapidly adapt to environment

Host in poor condition - immunocompromised, malnourished

Question 4

Is adherence an essential first step in the disease process?

Answer 4

No but it helps in areas where bacteria needs help to hang on

Question 5

What are the four bacterial adhesion forces?

Answer 5

Van der waals forces (+ve)

Electrostatic forces (-ve)

Hydrophobic interactions (+ve)

Specific interactions (+ve)

Question 6

What is motility used for?

Answer 6

To overcome -ve forces i.e. electrostatic forces

Question 7

What are the four types of arrangement of flagella?

Answer 7

Monotrichous - single polar

Amphitricious - single bipolar

Lophotricious - multiple polar

Peritricious - multiple over entire cell

Question 8

What are the three types of adhesive interactions?

Answer 8

Hydrophobic interactions
- two non-polar molecules

Cation-bridging
- cation will link the -ve surface and -ve bacteria

Receptor-ligand binding
- certain surface receptors bind to certain bacteria ligand

Question 9

Which bacteria aren’t as susceptible to antibiotics?

Answer 9

Bacteria with biofilms

Question 10

Why do bacteria adhere?

Answer 10

Causes changes in the bacterium, such as:

• growth rate
• carbohydrate metabolism
• energy generation
• gene expression
• production in exopolymers

Question 11

What effect do the bacterium changes have as a result of bacteria adherence?

Answer 11

Increase virulence and leads to host cell changes, such as:

• Morphological changes
• Fluid loss
• Express intercellular adhesion molecules
• Release of pathogen chemoattractant
• Decreased mucin secretion
• Cytokine release
• Matrilysin release
• Invasion
• Cell death
• Apoptosis

Question 12

How do bacteria penetrate the epithelia?

Answer 12

Through cells by inducing changes in the cytoskeleton, i.e. Actin and Microtubules

Between the cells by penetrating through cell junctions