Introduction

Question 1

What is an infection?

Answer 1

Invasion of a hosts tissue by micro-organism

Disease abused by:

• Microbial multiplication
• Toxins
• Host response

Question 2

What is the difference between infection and colonisation?

Answer 2

Infection involves the host responding badly, microbial multiplication and toxins.

Whereas, colonisation is when the microbes just live on us and don’t cause disease.

Question 3

How do people get infection?

Answer 3

From themselves - eg if pneumonia goes from throat to lungs (when comatose) it will then cause disease.

Animals

Environment

Source - either via an intermediate or not

Question 4

What is microbiota?

Answer 4

= commensals.

This describes micro-organisms carried on skin and costal surfaces.

Normally harmless or even beneficial - eg bacteria in colon produce vitamins

If these bacteria transfer to other sites then they can be harmful

Question 5

How are infections spread?

Answer 5

Physical contact - eg STIs

Airborne spread may be sufficient for other infections eg chickenpox - droplet or aerosol.

Vector may be necessary eg mosquito for malaria.

Environment eg Food or Water - legonellea bacteria spread in water - causes. Legonairs disease (SPELLING?!)
E. Colli 0157 in gut of cows can contaminate dairy (or meat) - cause very dangerous infection.

Question 6

What are the two types of transmission of disease?

Answer 6

Horizontal transmission

• Contact (direct, indirect, vectors)
• Inhalation (droplets,aerosols)
• Ingestion

Vertical transmission
-mother to child, before or at birth

Question 7

How do bacteria cause disease?

Answer 7

1. Expose
2. Adherence -to human surface
3. Invasion
4. Multiplication
5. Dissemination

Inc. Virulence factors (produce by organism nd release into environment)
Host cellular dangers

Question 8

What are virulence factors?

Answer 8

Exotoxins - cytolytic, AB toxins (PBL), superantigens, enzymes
Endotoxins - From the bacterial cell once dying

Question 9

How does the virus cause host cellular damage?

Answer 9

This can be due to direct consequence of microorganism or host immune response.

• Damage
• Consequent to host immune response

Question 10

What are the 4 P’s of infection?

Answer 10

Patient

• virulence factors
• inoculum size
• antimicrobial resistance

Pathogen

• site of infection
• co-morbidities eg diabetes makes them more likely to get an infection (E. coli)

Question 11

How do we know patients have an infection? (What questions to answer?)

Answer 11

Is there an infection?
Where is the infection
What is the cause of the infection?
What is the best treatment?

Question 12

How do we know if patients have an infection?

Answer 12

History 
-symptoms 
—focal, systemic 
—severity 
—durations 
-potential exposures 

Examination
-organ dysfunction

Investigations

• specific
• supportive

Question 13

What different types of investigations can we do to see if patients have an infection?

Answer 13

Supportive investigations

• full blood count - neutrophils, lymphocytes
• C reactive protein (CRP) - produced during inflammation
• Blood chemistry - liver and kidney function tests
• Imaging - x-ray, ultrasound. MRI
• Histopathology

Bacteriology (Grow organism on agar plate)
-Specimen types (swaps, fluids, tissues)
-M, C and S
—Microscopy (bacterial cells eg gram stain, patient cells eg CSF)
—Culture
—Antibiotic susceptibility
-Antigen detection
-Nucleic acid detection

Virology

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