| ID | • GPC • Catalase pos • Grow fast 🡪 appear as clusters • Differentiated in lab by presence of coagulase factors – agglutination test historically:

◦ GPC, Clusters, Cat pos, Coag neg = CoNS
◦ GPC, Clusters, Cat pos, Coag pos = Staph aureus |

| --- | --- | | Site | • Skin/soft tissue • GI tract/Mouth (?transient?) • URT (~25%) • Vaginal flora sometimes | | Clinical syndromes | - SOFT PAINS - SSTI - OM - Food Poisoning - TSS - Pneumonia - Arthritis - Infective endocarditis - Nec Fasc - Sepsis

• I hate SOFTPAINS. These break down to:
  • Skin, bone & joint (i.e. soft and hard tissue)
  • GI
  • Chest (lung & heart)
  • Toxic shock | | Risk Factors | • Barrier breakdown (cut, trauma, ulcer, PWID) • Immunocompromised (CKD. DM) • Prosthetic material (IVC, joints, valves) | | Pathogenic mechanisms | Virulence factors • Enzymes, cytotoxins & haemolysins (all strains) 🡪 convert normal tissue into nutrients • Panton-Valentin Leukocidin 🡪 Skin abscesses / necrotizing LRTI • Exfoliative toxins 🡪 Scalded Skin Syndrome • Enterotoxins 🡪 Food Poisonins • TSST-1 🡪 Toxic shock
    NB: TSST=1 and Enterotoxins are superantigens | | Lab ID | MSSA: • Constitutuve penicillinase (BlaZ); ~25% MSSA is ‘susceptible’, but may be masking plasmid-borne BlaZ • Antistaph penicillins are resistant to this: • Methicillin was first, but wasn’t acid-stable • Oxacillin second, then Fluclox/Diclox etc.

MRSA: • PBP2a or PBP2’: Site of binding for beta lactam is buried by conformational change • Coded by MecA/MecC gene, encoded within SCC (Staphylococcal Chromosomal Cassette) • Hospital MRSA: Lots of resistance genes in SCC 🡪 MDR • Commuity MRSA: Small SCC 🡪 limited resistance profile; lives on skin; more virulent SSTIs

BORSA: • MoA: hyperproduction of beta-lactamases or point mutations in PBPs. • Oxa R, Cefox S (Cefox is a better detector of MecA resistance) • Oxacillin MIC 1-8 • ?What to do with this information?

Vancomycin Resistance: • MIC <2: VSSA • MIC 4-8: VISA (polygenic changes in cell wall synthesis) • MIC >16: Borrowed VanA gene from enterococcus. | | Rx | • Fluclox if you can; nothing kills Staph like Fluclox – IF IT’S SENSITIVE • Co-amox / PipTaz also cover (BLI inhibits the constitutive penicillinase, allowing the amoxicillin/piperacillin to kill the staph)

• Cephalosporins (Ceftriaxone if CNS penetration needed) ◦ MRSA: Ceftaroline ◦ Once daily theoretical concerns about time over MIC ◦ Cefazolin in USA. Good for dialysis

• Carbapenems

• Glycopeptides ◦ Vancomycin ◦ Teicoplanin

• Aminoglycosides ◦ Gentamicin

• Macrolides ◦ Clarithromycin

• Tetracyclines ◦ Doxycycline

• Clindamicin ◦ Esp. if toxin production

• Quinolones ◦ Ciprofloxacin ◦ Levofloxacin

• Linezolid • Daptomycin (unless LRTI) • Cotrimoxazole

Always get source control first | | Vaccine | None |

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Old prep note available here:

01_Staph aureus.docx