1. Intro to Infection Flashcards
What is an infection?
Invasion of a host’s tissues by micro- organisms
Disease caused by:
– microbial multiplication – toxins
– host response
What are commensal bacterial and how can they cause infection?
– micro-organisms carried on skin and mucosal surfaces
– normally harmless or even beneficial
– transfer to other sites can be harmful
What are modes of horizontal transmission of an infection?
Contact - direct, indirect, vectors
Inhalation - droplets, aerosols
Ingestion -faecal-oral
What is vertical transmission of an infection?
From mother to child, before or at birth
How do micro-organisms cause disease?
Virulence factors can cause host cell damage directly or indirectly by activating the host response.
What are the 2 categories of virulence factors?
Endotoxins
Exotoxins
Name examples of exotoxins.
AB toxins, superantigens, enzymes, cytolytic
What patient factors may influence the disease severity/occurance?
- site of infection
- co-morbidities
- immune system
- age
What pathogen factors will influence disease progression?
Virulence factors
Antimicrobial resistance
Inoculum size
What supportive investigations can help determine whether a patient has an infection?
- FBC - lymphocytes, neutrophils
- CRP
- Liver and kidney function tests
- Imaging - XRay, ultrasound, MRI
- Histopathology
How can virology help to diagnose an infection?
- Antigen detection (on the virus)
- Antibody detection (patient response)
- Detect viral nucleic acid (DNA or RNA)
Which WBC would you expect to be raised in a bacterial infection?
Neutrophils
Which WBC would you expect to be altered in a viral infection?
Lymphocytes - may be raised or lowered
What is chocolate agar?
Some bacteria are inhibited by the presence of the blood (Haemophilus influenza) and will only grow if the blood cells have been lysed, releasing intracellular nutrients. The lysed blood is a darker brown colour and is called ‘chocolate agar’.
Why are agar plates red?
The standard Agar plate is red due to the addition of blood.
It is therefore an ‘enriched’ medium as the plate with the protein and blood provides nutrients for a number of common bacteria.
