General Microbiology — SCT I [Vol. 2]

Question 1

Describe precisely what toxoid means!

Answer 1

Inactivated bacterial exotoxin that is not toxic but immunogenic

Question 2

Mention 2 infectious diseases that can be prevented by vaccines containing toxoids!

Answer 2

Diphtheria & tetanus

Question 3

What does the DTaP vaccine contain?

Answer 3

Diphtheria, tetanus toxoids, and acellular pertussis vaccine

Question 4

What does the vaccine against tuberculosis (BCG) contain?

Answer 4

Live attenuated Myobacterium Bovis

Question 5

Specify the 4 groups of bacterial vaccines (classified according to the nature of the bacterial component)!

Answer 5

1. live, attenuated vaccines
2. killed (inactivated) bacterial vaccines
3. toxoid vaccines
4. subunit vaccines

Question 6

What are the main advantages and disadvantages of live attenuated vaccines as compared to killed vaccines?

Answer 6

Advantages: inducde not only serum antibodies but also cellular immunity and local IgA antibodies. Usually fewer doses needed and could be applied orally

Disadvantages: May revert to virulent in rare cases, and may cause disease in immunosuppressed patients. Live attenuated microbes are usually heat sensitive and must be refrigerated

Question 7

Mention 2 bacterial exotoxins that act by ADP ribosylation!

Answer 7

1. Diphtheria toxin
2. Cholera toxin
3. Pertussis toxin

Question 8

Mention 2 bacterial exotoxins that are neurotoxic!

Answer 8

1. Tetanus toxin
2. Botulinum toxin

Question 9

What is the mechanism of action of diphtheria toxin?

Answer 9

Inhibition of protein synthesis by ADP-ribosylation of ribosomal EF-2 (in eukaryotic cells)

Question 10

What is the mechanism of action of tetanus toxin?

Answer 10

Causes spastic paralysis by blocking the release of inhibitory neurotransmitters like GABA

Question 11

Mention at least three of the physiological effects of septic shock (characterized by the presence of large amount of bacterial endotoxin in the blood)!

Answer 11

1. Fever
2. Hypotension
3. Hypoglycaemia
4. Impaired organ perfusion

Question 12

Mention 2 non-essential bacterial organelles that enhance bacterial virulence! Describe how their function contributes to pathogenicity!

Answer 12

Capsule: antiphagocytic effect, adhesion to tissues

Fimbrae: binding to tissues

Flagellae: Spreading the bacteria

Question 13

Mention 4 extracellular enzymes of bacterial origin functioning as virulence factors!

Answer 13

1. IgA protease
2. Collagenase
3. Elastase
4. Urease

Question 14

What is a vector? Write an example!

Answer 14

Vector is an arthropod that transmits infection from human to human, or from animal to human

Examples: mosquito-malaria

Question 15

What is a reservoir? Write an example!

Answer 15

Normal host of a pathogen (animal or human) serving as a continuous source of infection to other hosts

Example: Humans-Salmonella Typhi

Question 16

Mention at least 5 possible transmission ways of infections!

Answer 16

1. Blood
2. Vectors
3. Faecal-oral
4. Direct contact (such as sexual)
5. Respiratory droplets

Question 17

[36] Mention 2 infectious diseases that are transmitted to humans by tick bites!

Answer 17

1. Tick-borne encephalitis
2. Lyme disease

Question 18

[25] What is the nature of antigen in the vaccines used to prevent infections by Streptococcus pneumoniae, Haemophilus influenzae and Neisseria meningitidis?

Answer 18

Capsular polysaccharide

Question 19

What is the difference between prevalence and incidence of an infectious disease?

Answer 19

Differentiated in chronic diseases.

Prevalence: total # of diseases per 100,000 people

Incidence: number of new cases in a year per 100,000 people

Question 20

What is the difference between mortality and case fatality rate of a disease?

Answer 20

Mortality: total # of deaths caused by disease in a population of 100,000 in a year

Case fatality rate: rate of death (%) among patients suffering from the disease