Staphylococcus aureus Flashcards
What is s.aureus?
Gram +ve cocci which is usually commensal, found within 3rd of population
What is coagulase?
- enzyme targets fibrinogen, which is most abundant protein in plasma
- converts soluble fibrinogen into insoluble fibrin
What happens to coagulase +ve bacteria?
Once incubated in plasma, clots will form due to conversion of fibrinogen to fibrin
Where is s.aureus usually located?
Usually nasopharynx tissues, but can also colonise nose, throat and urogenital tract
What causes conditions such as impetigo and scalded skin syndrome?
Exfoliative toxins target desmagline in the skin which cause intense symptoms
Colonised vs uncolonised patient risks
Colonised = more likely to acquire staph infection
Uncolonised = more serious infections when acquired
What is the core genome?
Highly conserved genes amongst all strains in the species
What is the accessory genome?
Strain dependent, adapted for specific niche
What is the pangenome?
All genes identified across all strains of a specific species
What does it mean by open pangenome?
Novel genes are still being found when sampling
What are genomic islands?
Found within accessory genomes, harbour genes associated with survival in different niches
Can be called pathogenicity islands if they encode for antibiotic resistance or virulence factors
What gene encodes resistance and how does it work?
- mecA gene, it encodes for an alternative penicillin binding protein in the bacterial cell wall
- has lower affinity for beta lactams and confer resistance effects
What sort of virulence factors are produced?
- cell wall
- capsule
- toxins
- enzymes eg. Coagulase
- MSCRAMMS
What are MSCRAMMs?
Microbial surface components recognising adhesive matrix molecules
- surface ashesins which have a signal peptide which is recognised by secretory apparatus of bacteria
What different regions of MSCRAMMs?
- S - signal peptide
- A domain - active ligand binding domain, binds to receptor in the host
- R region - acts as stalk to extend protein away from bacterial surface so can interact with its receptor
M - cell wall anchor with motif
What does fibronectin binding protein do?
Binds fibronectin, foms a cross bridge with major fibronectin integron receptor in the host cell, induces uptake of bacterial cell into the host cell
How does alpha toxin work?
Forms a heptameric pore, binds to receptor on the membrane, forms pore resulting in lysis of cell
Why is alpha toxin produced?
Lyses erythrocytes, allowing bacteria to gain access to iron required for growth and survival, losing the cell releases it
What is PVL?
PVL is a toxin produced at high levels, is encoded in bacteriophages and inserted into the genome
Is a member of leukocidins which target and lyse white blood cells, causing tissue damage
At low concentrations induces inflammatory response
