Staphylococci

Question 1

What is the 2 common foci of S.aureus CAI?

Answer 1

Bone/Joint
Heart

Question 2

What is associated with S.aureus HAI?

Answer 2

Lines

Question 3

How to classify S.aureus?

Answer 3

Gram positive cocci in clusters
Catalase positive
Coagulase positive

Question 4

What is the source of Staphylococci?

How about coagulase negative staph?

Answer 4

Skin

Coagulase negative staph impt part of normal skin flora

Question 5

Where is S.aureus carried?

Answer 5

Carried by about 30% of normal population at anterior nares/other sites

Question 6

Virulence factors of S.aureus

Answer 6

1. Protein A (cell-wall associated adhesion molecule)
2. Coagulase cause tissue damage(extracellular proteins )
3. Alpha toxin - pore forming haemolysin which lyses many host cell types (epithelial, endothelial, monocytes, macrophages, neutrophils)
4. Enterotoxins - food poisoning
5. Toxic shock syndrome toxin 1 (TSST-1)
6. Epidermolytic toxins

Question 7

Features of S.aureus enterotoxin

Answer 7

• Multiply at room temperature in some contaminated foods
• Tolerates high salt concentration

Question 8

What does S.aureus enterotoxin cause?

Answer 8

Rapid onset of symptoms (preformed enterotoxin)
- Vomiting prominent but diarrhoea may also occur)

Question 9

Where does S.aureus enterotoxin originate?

Answer 9

Food handler colonised/infected with enterotoxin-producing strain

Question 10

What does S.aureus TSST-1 lead to?

Answer 10

Superantigen cross-links MHC II to TCR away from complementary determining region
Many T cells activated with massive release of cytokine (cytokine storm) and shock develops -> multiorgan failure, death

Question 11

What does S.aureus epidermolytic toxins cause?

Answer 11

• Scalded skin syndrome
• SSTI: folliculitis, impetigo, boil, carbuncle, cellulitis, wound infection at surgical sites
• Localised pemphigus neonatorum, bullous impetigo (often results in abscess/pus)
• Generalised (large areas of skin lost): Ritter’s disease in neonates, toxic epidermal necrolysis in adults

Question 12

What diseases does S.aureus cause?

Answer 12

1. Osteomyelitis
2. Septic arthritis
3. Acute endocarditis (esp. in IVDA, tricuspid valve of right side)
4. Pneumonia following influenza
5. SSTI
6. Toxic shock syndrome
7. Food poisoning
8. Abscess of any tissue/organ (brain, kidney, muscle)

Question 13

How to treat S.aureus?

Answer 13

1. Drain pus (remove foreign material and dead tissue)
2. Cloxacillin/co-amoxiclavs/cephalosporins
3. Erythromycin
4. MRSA: Vancomycin, ceftaroline/ceftobiprole
5. Topical agent Mupirocin

Question 14

How does MRSA arise?

Answer 14

PBP2
Gene mecA imparts resistance to beta-lactam antibiotics (penicillins, cephlasporins, carbapenems)

Question 15

What are the typings available?

Answer 15

AMR profiles
Sequence (multilocus, whole genome)

Question 16

What is a problem with coagulase negative Staphylococci?

Answer 16

Contaminate blood cultures
Device associated infections (lines, prostheses)

Question 16

Examples of coagulase negative staphylococci

Answer 16

S. epidermidis, S.saprophyticus, S.lugdunensis

Question 17

What are coagulase negative Staphylococci resistant to?

Answer 17

Vancomycin

Question 18

What does S.saprophyticus cause? How to treat?

Answer 18

UTI in sexually active young women
Co-trimoxazole

Question 19

What to assess for S.lugdunensis ? What is the flora?

Answer 19

Endocarditis as it behaves like S.aureus
Perineal flora