Commensalism and pathogenesis

Question 1

Examples of sterile sites in the body

Answer 1

Urine

Blood

Cerebrospinal fluid

Bone marrow

Pleural fluid

Presence of bugs in this sight could be clinically significant or indicate contamination.

Question 2

Non-sterile sites in the body

Answer 2

Skin

Respiratory tract

Question 3

Commensals

Answer 3

Normal flora of bacterial organisms in the body, present in non-sterile sites.

Commensal flora can shift and cause disease through opportunistic infection

Question 4

Mechanism of pathogenic mechanisms

Answer 4

1. Adhesion: bacteria could contain adhesins which allow it to stick to host cells.
   Fimbrial adhesins are seen in E. coli.
2. Invasion: usually occurs when immune system is compromised.
   Invasion can be superficial, such as ringworm.

3.Overcoming of the immune system:
Mechanisms to resist immune attack such as a capsule, cloaking in host proteins.

4. Multiplication:
   Enzymes produced to overcome immune system.
   Toxins used
5. Dissemination around host:
   Hematogenous or lymphatic spread

Question 5

Mechanisms that allow pathogens to survive

Answer 5

Capsule:
Forces the immune system to change to adaptive. This takes more time, giving time to multiply.

Cloaking in host proteins:
Protein A in S. aureus is able to bind with the Fc region of IgG.
Proteins can be produced to bind to antibodies
Schistosomes

Toxins:
Endotoxins (LPS)- stimulates overwhelming immune resposne
Exotoxins - cytolysins which cause osmotic blow up of cells

Question 6

Environmental factors that influence susceptibility to disease

Answer 6

Climate: Could increase spread of disease through crowding.
Affects distribution of pathogens and vectors.

Sanitation

Population density

Herd immunity

Presence of vectors

Question 7

Genetic factors that affect susceptibility to infections

Answer 7

Certain genetic conditions can make you more/less likely to get an infection:

Sickle cell- protected against malaria

Cystic fibrosis:
Protected against cholera and typhoid.
More likely to get pseudomonas infections in respiratory tract.

Question 8

Examples of immunocompromised factors that could influence infections

Answer 8

HIV/AIDS- reduced immune function.

Splenectomy- less memory B cells, increased likelihood of sepsis.

Burns- decreases skin integrity.