Week 1 - Introduction to Infection and Microbes

Question 1

Describe the function and characteristics of the red pulp of the spleen.

Answer 1

• Red pulp receives arterial blood which passes into the venous sinuses
• Lined by macrophages which remove old red cells and recycle iron

Question 2

What is cellulitis?

Answer 2

Non-necrotising inflammation of skin and subcutaneous tissue

Question 3

State two organisms that are commonly implicated in cellulitis.

Answer 3

Staphylococcus aureus

Streptococcus pyogenes

Question 4

Define exotoxins.

Answer 4

Bacterial toxins that can cause local or distant damage

Question 5

Define endotoxins.

Answer 5

Stimulate macrophages to produce cytokines such as interleukin-1 and tumour necrosis factor that cause fever and shock

Question 6

State the functions of the lymphatic system.

Answer 6

1. Fat absorption
2. Fluid balance
3. Defence

Question 7

Describe the structure of a lymph node.

Answer 7

Cortex: follicles with germinal center - contains dividing lymphocytes
Medulla: contains phagocytic macrophages

Question 8

Define lymphadenitis.

Answer 8

Swollen painful lymph node responding to a foreign antigen

Question 9

State two functions of the thymus.

Answer 9

1. Produces lymphocytes

2. Produces a protein hormone thymosins

Question 10

State the two tissue types present in spleen and outline what each of them contain.

Answer 10

Red pulp: red blood cells and macrophages

White pulp: contains lymphocytes

Question 11

Outline the structural features of adenovirus.

Answer 11

DNA
Capsid
No envelope

Question 12

Which parasitic protozoan can cause diarrhoea?

Answer 12

Cryptosporidium

Question 13

State Koch’s postulates.

Answer 13

1. The microorganism must be found in abundance in all organisms suffering from the disease, but should not be found in healthy organisms.
2. The microorganism must be isolated from a diseased organism and grown in pure culture.
3. The cultured microorganism should cause disease when introduced into a healthy organism.
4. The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

Question 14

What is infection?

Answer 14

Invasion of a host’s tissues by microorganisms

Question 15

How is disease caused by microorganisms?

Answer 15

1. Microbial multiplication
2. Host response
3. Toxins

Question 16

How is chicken pox spread?

Answer 16

Airborne

Question 17

What are the ways in which people can get infected?

Answer 17

1. Physical contact, e.g. STIs
2. Airborne, e.g. chicken pox
3. Vector may be necessary, e.g. mosquito for malaria
4. Ingestion of contaminated food or water
5. Inhalation of air contaminated with environmental organisms
6. Contact with contaminated surfaces, e.g. medical devices

Question 18

Outline the modes of horizontal transmission.

Answer 18

1. Contact: direct, indirect, vectors
2. Inhalation: droplets, aerosols
3. Ingestion - faecal oral transmission

Question 19

Outline the disease determinants related to the pathogen.

Answer 19

1. Virulence factors
2. Inoculum size
3. Antimicrobial resistance

Question 20

Outline disease determinants related to the patient.

Answer 20

1. Site of infection

2. Co-morbidities

Question 21

Outline supportive investigations that can be carried out for a patient with infection.

Answer 21

1. Full blood count: neutrophils, lymphocytes
2. CRP
3. Blood chemistry: liver and kidney function tests
4. Imaging: X-ray, ultrasound, MRI
5. Histopathology

Question 22

Outline the specific investigations that can be carried out for a patient with bacterial infection.

Answer 22

1. Specimen types: swabs, fluids and tissues
2. M, C &S: Microscopy - bacterial cells (e.g. Gram stain), patient cells, e.g. cerebrospinal fluid, culture, antibiotic susceptibility
3. Antigen detection
4. Nucleic acid detection

Question 23

Outline the specific investigations that can be carried out for a patient with viral infection.

Answer 23

• Antigen detection: the virus
• Antibody detection: patient’s response
• Detecting viral nucleic acid (DNA/RNA)

Question 24

Why are asplenic patients susceptible to infection by encapsulated bacteria?

Answer 24

1. Encapsulated bacteria are more likely to produce overwhelming sepsis/meningitis in asplenic patients since without a spleen, the patient is deficient in macrophages
2. Responsible for clearing opsonised, encapsulated bacteria