Staphylococcus aureus

Question 1

What is s.aureus?

Answer 1

Gram +ve cocci which is usually commensal, found within 3rd of population

Question 2

What is coagulase?

Answer 2

• enzyme targets fibrinogen, which is most abundant protein in plasma
• converts soluble fibrinogen into insoluble fibrin

Question 3

What happens to coagulase +ve bacteria?

Answer 3

Once incubated in plasma, clots will form due to conversion of fibrinogen to fibrin

Question 4

Where is s.aureus usually located?

Answer 4

Usually nasopharynx tissues, but can also colonise nose, throat and urogenital tract

Question 5

What causes conditions such as impetigo and scalded skin syndrome?

Answer 5

Exfoliative toxins target desmagline in the skin which cause intense symptoms

Question 6

Colonised vs uncolonised patient risks

Answer 6

Colonised = more likely to acquire staph infection
Uncolonised = more serious infections when acquired

Question 7

What is the core genome?

Answer 7

Highly conserved genes amongst all strains in the species

Question 8

What is the accessory genome?

Answer 8

Strain dependent, adapted for specific niche

Question 9

What is the pangenome?

Answer 9

All genes identified across all strains of a specific species

Question 10

What does it mean by open pangenome?

Answer 10

Novel genes are still being found when sampling

Question 11

What are genomic islands?

Answer 11

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

Question 12

What gene encodes resistance and how does it work?

Answer 12

• 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

Question 13

What sort of virulence factors are produced?

Answer 13

• cell wall
• capsule
• toxins
• enzymes eg. Coagulase
• MSCRAMMS

Question 14

What are MSCRAMMs?

Answer 14

Microbial surface components recognising adhesive matrix molecules

• surface ashesins which have a signal peptide which is recognised by secretory apparatus of bacteria

Question 15

What different regions of MSCRAMMs?

Answer 15

• 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

Question 16

What does fibronectin binding protein do?

Answer 16

Binds fibronectin, foms a cross bridge with major fibronectin integron receptor in the host cell, induces uptake of bacterial cell into the host cell

Question 17

How does alpha toxin work?

Answer 17

Forms a heptameric pore, binds to receptor on the membrane, forms pore resulting in lysis of cell

Question 18

Why is alpha toxin produced?

Answer 18

Lyses erythrocytes, allowing bacteria to gain access to iron required for growth and survival, losing the cell releases it

Question 19

What is PVL?

Answer 19

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