Lecture 5, 6, 7 Host parasite pathogenesis

Question 1

What is resident flora and transient flora

Answer 1

Resident flora/normal flora are fixed microbes which are constantly in/on the skin, if disturbed they will replenish themselves (can be opportunistic)
Transient flora are non-pathogenic/potentially pathogenic organisms that inhabit the skin/mucous membranes for hours to weeks

Question 2

What are opportunistic pathogens

Answer 2

Opportunist pathogens are unable to infect healthy host unless their is an impairment in surface or systemic defences

Question 3

What are some of the factors that host defences are impaired by (5)

Answer 3

1. Burns
2. Insertion of foreign bodies (catheters)
3. Viral infections
4. Immunosuppressive drugs or diseases (AIDS)
5. Antibiotic therapy (disrupt normal flora)

Question 4

What are factors which affect the likelihood of disease (7)

Answer 4

1. Infecting dose
2. Age
3. Route
4. Sex
5. Presence of other microbes
6. Nutritional status
7. Genetic background

Question 5

Describe the entry of a pathogenesis of infectious disease through the skin and the barriers (3)

Answer 5

Infections through the skin is usually through wounds where opportunistic pathogens attack the wound (S.aureus) or Y.pestis (flea bite plague).
The barriers are
1. Dryness (bacteria like moisture)
2. FFAs
3. Shedding

Question 6

Describe the entry of a pathogenesis of infectious disease through inhalation and the barriers (4)

Answer 6

Bacteria is inhaled and infection is spread by aerosols in new host’s respiratory tract
The barriers are:
1. Nasal turbinates
2. Mucociliary escalator (Mucous forces things up)
3. Alveolar macrophages
4. Secretory IgA

Question 7

Describe the entry of a pathogenesis of infectious disease through ingestion and the barriers (6)

Answer 7

Bacteria is ingested in food and can also be protected by the food making it hard for the barriers to remove the bacteria 
The barriers are:
1. Transit time (takes a while)
2. Mucus (traps molecules)
3. Stomach acid (high pH kills)
4. Digestive enzymes (digest food and bacteria)
5. Bile 
6. Secretory IgA

Question 8

Describe the entry of a pathogenesis of infectious disease through the uriogenital tract and the barriers (4)

Answer 8

Infection usually due to inserting of catheter
Barriers are:
1. Mucus
2. Flushing of urine
3. Bladder normally sterile
4. Female vaginal epithelium contain glycogen which lactobacilli metabolise to produce lactic acid pH 5

Question 9

Describe the attachment of a pathogenesis of infectious disease

Answer 9

Bacteria attach with fimbrae/pili, other surface proteins (OMPs) and surface polysaccharides

Question 10

Describe the 3 ways bacteria spread of a pathogenesis of infectious disease

Answer 10

1. None, organisms remain localised
2. Penetrate epithelium (Shigella grow in submucosa)
3. Spread to other parts of the body (Y.pestis via blood)

Question 11

Define bacteraemia

Answer 11

Bacteraemia is when bacteria is in the blood transiently (transported in blood)

Question 12

Define septicaemia, its symptoms (3) and complications (3)

Answer 12

Septicaemia is when bacteria multiplies in the blood
Symptoms include:
fever, chills and prostration
Complications include:
1. Septic shock resulting in vascular collapse
2. Acute renal failure
3. disseminated intravascular coagulation (DIC)

Question 13

Describe the multiplication of a pathogenesis of infectious disease

Answer 13

Initial inoculum/concentration of bacteria rarely sufficient to cause disease, so pathogen must find sufficient nutrients and suitable environmental conditions

Question 14

Describe the 3 results of a bacterial pathogenesis of infectious disease

Answer 14

1. Exotoxins
2. Endotoxins
3. Host response

Question 15

What are exotoxins, what are they encoded by (3) and the 4 targets

Answer 15

Exotoxins are toxins excreted by the bacteria (usually proteins). They are encoded by chromosomes, plasmids and lysogenic bacteriophage.
The usual targets are
1. nerves (neurotoxins)
2. Gut (enterotoxins)
3. red blood cells (haemolysins)
4. actin filament formation in cells (cytoskeletal toxins)

Question 16

What are the 5 mechanisms of action for exotoxins

Answer 16

1. Damage cell membranes (cytolytic proteins)
2. Inhibit protein synthesis (AB toxins)
3. Activate secondary messenger pathways (AB toxins)
4. Activate host immune response (superantigens)
5. Digest proteins (proteases)

Question 17

What are endotoxins and what do they cause (3)

Answer 17

Endotoxins are the lipopolysaccharide layer in gram -ve bacteria, they are released by the cells as blebs or when they lyse, they cause

1. Fever
2. Hypotension
3. Disseminated intravascular coagulation

Question 18

What are intracellular pathogens

Answer 18

Intracellular pathogens can avoid host defences (antibody and complement) by replicating inside host cells, including macrophages. They can also disrupt the fusion of the phagolysosomes or remain in phagosome to delay fusion which kill the bacteria

Question 19

Describe the exit of a pathogenesis of infectious disease and what transmission of the disease depends on (3).

Answer 19

Nearly all microbes are shed from body surfaces (route to new host)
Transmission depends on:
1. number of organisms shed
2. Stablility in environment 
3. Infectious dose required

Question 20

What are the 4 Koch’s Postulates

Answer 20

Four criteria designed to establish a relationship with a microbe and a disease
1. The microbe must be present in every
case of the disease.
2. The microbe must be isolated from the
diseased host and grown in pure culture.
3. The disease must be reproduced when a
pure culture is introduced into a nondiseased,
susceptible host.
4. The microbe must be recoverable from an
experimentally infected host.