CSIM 1.35 Endotoxins Exotoxins and Virulence Factors

Question 1

What is the difference between pathogenicity and virulence?

Answer 1

Pathogenicity is qualitative and represents whether or not a bacterium is pathogenic

Virulence is quantitative and represents how severe that pathogenesis is

Question 2

What are the factors that determine virulence?

Answer 2

• Adhesion
  
  • Invasion
  • Motility
  • Survival
  • Growth
  • Toxins

Question 3

What type of bacteria are fimbriae found on?

Answer 3

Gram negative bacteria, as the fimbriae require an outer membrane for attachment

Question 4

Describe fimbrial assembly.

Answer 4

• Unfolded polypeptide chains are transported across the inner membrane into the periplasmic space by Sec proteins
  
  • Here, the polypeptide chains are folded into their tertiary structure
  • These are arranged into a chain at FimD to form a pilus/fimbriae

IMG 87

Question 5

What is adhesin?

Answer 5

Proteins found on fimbriae which bind to sugars (such as those found on capsules)

Question 6

What are capsules made up of?

How does this aid with survival?

Answer 6

Polymers of repeating units of a sugar. This can be:
• Disaccharide
• Trisaccharide
• Trisaccharide with non-sugar modifications
• Four sugars

IMG 88

These are often sugars commonly used by the host, so the bacterium can ‘camouflage’ the cell from the immune system

Question 7

How is outer protection identified?

Answer 7

By using indirect staining to view the width of the capsule relative to the bacterium

IMG 89

Question 8

Which notable strains of bacteria use capsules?

Answer 8

• Streptococcus pneumoniae
  
  • Streptococcus pyrogenes
  • Bacillus anthracis
  • Neisseria meningitidis

Question 9

What are the patterns of arrangement of flagella

Answer 9

Monotrichous
• One flagellum

Polar Flagellum
• Monotrichous (one flagella) whereby the flagella is at the ‘end’ of the cell

Sub-polar flagellum
• Monotrichous (one flagella) whereby the flagella is almost at the ‘end’ of the cell (slightly off-centre)

Amphitrichous
• Two flagella
• One at each end of the cell

Lophotrichous
• Clusters of flagella at one or both ends of the cell

Peritrichous
• Spread over the entire surface of the cell

IMG 90

Question 10

Which arrangement of flagella dothe following have?

1) Legionella pneumophilia
2) Salmonella typhimurium

Answer 10

1) Sub-polar monotrichous

2) Peritrichous

Question 11

How do flagella cause movement?

Answer 11

They rotate anticlockwise to form a ‘propellor’ using hydrogen ion concentration gradients as a source of energy (like with respiration)

(IMG 91)

Question 12

What type of bacteria form bacterial endospores?

Answer 12

Gram-positive rods

e.g. anthrax

Question 13

How long can endospores survive?

Answer 13

Several years

Question 14

When does a bacterium form an endospore?

Answer 14

When growth ceases due to lack of nutrients or an unfavourable environment

Question 15

Describe the process of endospore formation

Answer 15

Survival mechanism:
• Bacterium replicates its DNA
• The two DNA copies polarise
• One copy gains a double forespore membrane inside the bacterium
• A cortex is formed between these membranes made of peptidoglygan (same as cell wall)
• Forms a spore coat
• Cell kills itself, leaving the endospore

IMG 92

Question 16

What are the two forms of bacterial toxins?
  •  Location
  •  Toxicity
  •  Immunogenicity
  •  Toxoid potential
  •  Fever inducing

Answer 16

Endotoxins 
  •  Lipopolysaccharides
  •  Weak toxicity
  •  Poor immunogenicity
  •  No toxoid potential
  •  Fever-inducing 

Exotoxins (e.g. neurotoxins, enterotoxins and cytotoxins)
• Released into the host
• High toxicity
• High immunogenicity
• High toxoid potential as it remains immunogenic after neutralisation

Question 17

What are the types of exotoxins?

Answer 17

Cytolytic toxins
• Lead to cell lysis

AB toxins
• Made up of 2 subunits
• B subunit which bind to specific cell receptors and facilitates the uptake of A
• A inhibits cellular processes or damages cell
• E.g. botox

Superantigens
• Overstimulate the immune system

Enterotoxins
• Act on the small intestine

Neurotoxins
• AB toxins which target nerve cells

Question 18

Which bacteria have endotoxins?

Answer 18

Gram negative bacteria (because external cell membrane must be present)