IA. General Microbiology | 14. Pathogenicity and virulence. The measurement of the virulence

Question 1

What do Koch’s Postulates state?

Answer 1

1. To show the direct correlation of certain microbe and a certain disease
2. The microbe should be present in the ill subjects and not in the healthy ones
3. We should be able to isolate and culture the microbe from the ill subject
4. The isolated microbe, if inoculated in a new host, should produce the same disease
5. The microbe should be regained from this new host, and be identical with the original microbe

Question 2

I. Pathogenicity
1. What is Pathogenicity?

Answer 2

the ability (of a given microbe) to cause infection in a given host(human, animal)
- Applicable at species level
- Wide and narrow host spectrum

Question 3

I. Pathogenicity
2. What are variations of Pathogenicity?

Answer 3

• Obligate pathogens (can only affect certain species)
• Facultative pathogens (normal flora-elsewhere)
• Opportunistic pathogens (immunosuppression)
• Pathogens (environmental only)

Question 4

II. Virulence
1. What is the definition of virulence?

Answer 4

the degree of the microbes’ ability to cause disease

Question 5

II. Virulence
2. What are the features of virulence?

Answer 5

• Applicable at population level within a species
• Loss of virulence= attenuation (vaccines!)
• Quantification of virulence
  +) ID50= infectious dose 50
  +) LD50= lethal dose 50

Question 6

III. Virulence factors
3. What are the 4 virulence factors?

Answer 6

1. Surface structures
2. Enzymes
3. Toxins
4. Biofilm formation

Question 7

III. Virulence factors
1A. List the 7 surface structures that act as virulence factors

Answer 7

• Capsule
• Pili, fimbriae
• Adhesisn
• F protein
• Protein A
• Lipoteichoic acid
• Invasins

Question 8

III. Virulence factors
1B. Why is capsule considered as a virulence factor?

Answer 8

• Helps cell avoid phagocytosis→ gives mechanical dense
• Found in H. influenzae, streptococcus pneumonia, Str. agalactiae, Neisseria meningitidis, E.coli
• Made of polysaccharide except for B.anthracis (poly-D-glutamic acid) and S.pyogenes (hyluronic acid)

Question 9

III. Virulence factors
2. Enzymes are also a virulence factor
=> Explain

Answer 9

1. For invasion and degradation
   - Hyaluronidase, collagenase, elastase, phospholipase, protease, DNAase, RNAase
2. To avoid host defense
   - Coagulase, IgA protease, leukocidin

Question 10

III. Virulence factors
3A. What are the 2 types of toxins?

Answer 10

• Exotoxins
• Endotoxins

Question 11

III. Virulence factors
3B. What are the features of exotoxins?

Answer 11

• Produced by bacteria
• Severe, special symptoms
• Can be attenuated to TOXOID (vaccination!)
• Cytolytic effect, inhibition of protein synthesis, hypersecretion of ions, neurotoxins
• Superantigens can activate many T cells → cytokine storm → life threatening immune response

Question 12

III. Virulence factors
3C. What are the features of endotoxins?

Answer 12

• Part of Gram NEGATIVE bacteria
• Released at cell death
• Lipid (poor antigen)
• Cannot be attenuated

Question 13

III. Virulence factors
4. How is biofilm formed?

Answer 13

1) Reversible absorption of bacteria becomes irreversible (sec-min)
2) Bacteria grow and divide (hrs-days)
3) Exopolymer produced and causes biofilm formation(hrs-days)
4) Other organisms attach to biofilm (days-months)