5.7 Colonisation + measuring Virulence

Question 1

Colonization: Production of Virulence Factors

Answer 1

Pathogens use various strategies to cause disease but often the general process of pathogenesis is similar

Colonization and growth production of virulence factors

1. Toxicity: toxins effects are local or systemic
2. Invasiveness: further growth at original and distant sites

Question 2

Measuring Virulence - LD50

Answer 2

Virulence: the relative ability of a pathogen to cause disease (measure of pathogenicity)

-> Virulence can be estimated from experimental studies: LD50 (lethal dose 50)

LD50: the amount of an agent that kills 50% of the animals in a test group

Measuring Virulence:

Highly virulent pathogens show little difference in the number of cells required to kill 100% of the population as compared to 50% of the population

Question 3

Study of Virulence Factors

Answer 3

• > Considerable research is done to identify and characterise virulence factors
• > Often deletion mutants used, meaning virulence factors are deleted and the strain is compared to wild-type in experimental infection in mouse or other tissue culture cells.
• > Molecular Koch’s postulates used to confirm the role of a virulence factor in infection.

1. ) The phenotype or property under investigation should be associated with pathogenic members of a genus or pathogenic strains of a species.
2. ) specific inactivation of the gene(s) associated with the suspected virulence trait should lead to a measurable loss in pathogenicity or virulence, or the gene(s) associated with the supposed virulence trait should be isolated by molecular methods. Specific inactivation or deletion of the gene(s) should lead to loss of function in the clone.
3. ) Reversion or allelic replacement of the mutated gene should lead to restoration of pathogenicity, or the replacement of the modified gene(s) for its allelic counterpart in the strain of the origin should lead to loss of function and loss of pathogenicity or virulence. Restoration of pathogenicity should accompany the reintroduction of the wild-type gene(s).

Question 4

Attenuation of a pathogen

Answer 4

Attenuation: the decrease or loss of virulence

• > Attenuated mutants are useful in research
• > Potential as vaccine candidates