Lecture 10- Staphylococcus aureus Flashcards
How common is Staphylococcus aureus? How is it spread?
1/5 people carry (usually in nose), much more common then meningitis. Not evenly spread due to population density, and is higher in cities. Higher in North island and in summer
SA is..
a common cause of disease, hospital-acquired infection, death.
An array of virulence factors.
Exists everywhere
Cellulitis
common staph infection that affects deeper layers of the skin.
What do staph aureus look like under microscope?
grape-like clusters, purple because their thick peptidoglycan cell wall takes up the stain.
Where does staph come from?
Predominantly human pathogen.
- human transmission to domestic animals can occur
eg) Bonvine mastitis. (pain suffering, reduced milk/growth in cows, cost to industry)
What can cause colonisation / disease
bacterial, host and environmental factors, + exposure»_space; colonisation (20-25%)»_space; disease
NOTE: bacteria usually always needs to colonise first before it can cause disease, therefore not all hosts get disease
When did cow staph occur?
~200 years ago when dairy farming became popular, cows in dense large populations. From humans to cows.
Where do you find staph infection sites on the body
SA carriers usually always carry SA in the nose (can handle noses salty environment)
-also many other places in the body
When is SA colonisation most common
First year of life (infected by mum)
-declines with old age
Different types of SA carriers, which is seen in the nose
Persistent: always have staph. Increased disease risk
Intermittent:
non-: Beta-3 defensins that fight bacteria. No/low risk of SA
What can SA do…
Food posioning: common, not from direct infection but from toxins.
Skin infection: 3%
Asymptomatic: 60%
SA and hair follicles.
Bacteria can fall into hair follicle, interacts with epithelial cells
- damaged cells release CKs, immune system is triggered.
- also chemotaxis recruits more cells to area.
How are bacteria dissolved??
A phagosome with bacteria in it is formed when the neutrophil injests bacteria. Toxic granules form around the lysosome, converting it to a lysosome. Bacteria gets dissolved by produced H202
With such an active IS, how is it that SA is ever able to infect us?
- use enzyme catalase changes H2O2> H20 and O2 so cant be killed in cell.
- Can kill off WBC with haemolysinz
- can use clumping factor to coat itself in fibrinogen and hide from the IS
- Covered in Protein A, binds to Human Ig the wrong way and hide from the immune system
Treatment if s. aureus
1) stabilise the patient
2) drain pus
3) antibiotics
