7 - Staphylococcus Flashcards
Is Staphylococcus gram positive or gram negative?
Gram positive
What shape is Staphylococcus?
Coccoid
How does Staphylococcus respire?
Facultative anaerobe
What medium is used to isolate Staphylococcus?
Mannitol salt agar:
- S. aureus causes colour change from pink to yellow (ferments mannitol)
- S. epidermidis does not cause a colour change
Blood agar
Baird-Parker agar:
- Coagulase positive Staphylococci form black colonies
Is Staphylococcus catalase positive or negative?
Catalase positive
How is S. aureus differentiated from other Staphylococcus species?
S. aureus is coagulase positive
How does S. aureus quorum sensing occur?
At high cell density:
- AIP binds to AgrC
- AgrC phosphorylates AgrA
- Phosphorylated AgrA binds P2 and P3 promoters
- Transcription of AgrBDCA and RNAIII
- RNA III induces expression of an array of virulence factors
What are the two main types of S. aureus infection and two examples of each?
Suppurative infections - pus production:
- Impetigo and osteomyelitis
Toxin mediated disease:
- Staphylococcal scalded skin syndrome (SSSS) and toxic shock syndrome
What are 3 important S. aureus virulence factors and their functions?
Slime layer - adhesion to tissue and formities
Secreted protein A - reduces opsonophagocytosis by binding Igs and BCRs
Aureolysin and SplB - degrade complement components and block neutrophil opsonophagocytosis
What are 4 S. aureus toxins?
Cytotoxins - form pores in membranes and kill leukocytes
Exfoliative toxins - ETA and ETB - SSSS
Enterotoxins - food poisoning
TSST-1 - TSS - leakage of endothelial cells and cytokine storm
What causes TSST-1 production in high-density conditions?
- RNAIII inhibits Rot expression freeing Ptst promoter
- Saer drives expression of tst by binding to Ptst promoter
- TSST-1 is produced
What 3 mobile genetic elements are present in resistant strains of S. aureus?
Tn5801 - encodes tetM - tetracycline resistance
Tn1546 - encodes VanA - vancomycin resistance
- SCCmec - encodes mecA - methicillin resistance
