Staph Aureus Flashcards
Where does Staph increase colonisation on an infected person
hand
axilla
forearm
nose
pharynx
Skin abdomen
perineum
Common cause of staph infection
Food posioning most of time (ingest preformed toxins that the Staph has already formed)
3% come from skin infection
Describe the process of Staph infection
1.Bacteria attempt to invade (eg in a hair follicle)
2. Some bacteria have the ability to interact/damage human cells. Most bacteria on the skin DO NOT interact with human cells
3. Damaged cells released cytokines that recruit immune cells to the site (chemotaxis)
4. More cytokines are released and nearby capilliaries open up and allow more WBC to squeeze of the vessel (diapedis) and move to the infection
5. cytokines irritate nerve fibres causing PAIN and blood flow chnages causing symptoms of inflammation
6. The ingested bacteria fuses with enzyme factories inside a neutrophul WBC and the enzyme releases chemicals to kill bacteria (lysoenzyme)
Examples of innate immunity resistance strategies of Staph aureus
- Neutrophil lysis
2.impairment of phagocyte recruitment - interference with complement activation
- Resistance to oxidative burst killing
- Resistance to antimicrobial peptides
- Nonopsonic binding or degradtion of immuniglobulins
4 ways it avoids making an immune response:
Protein A on Staph aureus binds a heavy chain IgG and masks SA from immune system. Therefore it coats itself in antibody (or clotting proteins, sugar capsules) to avoid being detected by WBC
Released chemicals (CHIPS) to prevent chemotaxis
Use catalase to breakdown hydrogen perioxide inside neutrophil
Release toxin hemolysin to destroy neutrophils allowing release of SA
Treatment
Stabilise person
Drain pus
Antibiotics -pencillin
Why does pencillin work as treatment?
It inhibits transpeptidase a bacterial enzyme that cross links the sugars of peptidoglycan (and provides structural intergrity to the bacterial cell wall) THUS it causes the bacteria to explode
Why did MRSA come about
The older version of pencillin was methicilin but SA got resistant to it
types of carriers of Staph aureus
- Persistent
- Non carriers
- Intermittent
Staph Aureus symptoms
Styus
Sinisitus
Pneumonia
endocarditis
Diarrhoea
Emesis
Cellulitis
UTI
Osteomyelytis
Toxic shock syndrome
What is invasive Staph Aureus
Infection in the blood stream
