Gram positive bacteria Flashcards
What colour do gram positive bacteria stain?
Purple
Why do gram positive bacteria stain purple?
Gram positive bacteria retain the colour of the crystal violet stain in the gram stain (because they have a cell wall composed of a thick layer of peptidoglycan)
What are examples of gram positive bacteria?
Staphylococcus
Streptococcus
What are staphylococcus and streptococcus?
aerobic gram positive cocci
Where is the normal habitat for staphylococcus?
Nose and skin
What test can be used to further distinguish between staphyloccoci?
Coagulase test
Which staphylococcus will be coagulase test positive?
S. aureus
What is s. aureus spread by?
aerosol and touch
What are virulence factors for s. areus?
- Pore-forming toxins (some strains)
- a - haemolysin & Panton-Valentine Leucocidin
- Proteases (exfoliating)
- Toxic Shock Syndrome toxin (stimulates cytokine release)
- Protein A (surface protein which binds Ig’s in wrong orientation)
What is an example of a staphylococcus that is coagulase test negative?
S. epidermidis
What type of infection does s. epidermidis cause?
Infections in debilitated, prostheses (opportunistic)
What is s. epidermidis main virulence factor?
- ability to form persistent biofilms
- Can stick to prostheses making difficult to treat
What is s. pyogenes?
Streptococcus pyogenes
- b-haemolytic, (group A)
What is s. pyogenes sensitive to?
Penicillin
What are some infections that s. pyogenes can cause?
- Wound infections → cellulitis, puerperal fever
- Tonsillitis & pharyngitis
- Otitis media
- Impetigo
- Scarlet fever
- Complications
- rheumatic fever
- glomerulonephritis
