Gram positives Flashcards
Classify Staph aureus
1) Gram +ve
2) Catalase +ve
3) Coagulate +ve
What medium is used to identify staph aureus?
Blood agar → ß hemolytic (complete/transparent)
Mannitol salt agar → pink to yellow
What are some virulence factors of staph aureus?
1) Protein A (cell wall)
2) Coagulase, enzymes
3) Toxins (TSST-1, α toxin, enterotoxins, epidermolytic toxins)
What are the common sources of Staph aureus?
1) Skin
2) Anterior nares (30%)
3) Food (mayo and meat) left out for too long
4) Lines
What are 4 toxins and their associated conditions in Staph aureus?
1) TSST-1 (Super Ag) → crosslink MHC2 and TCR away from CDR → cytokine storm → TSS/SIRS
2) Enterotoxin A-E → Food poisoning/satphylococcal enteritis
3) Epidermolytic toxin A and B → Scalded skin syndrome, Pemphigus neonatorum, bullous impetigo, Ritter’s disease, TEN
4) α toxin → haemolysin
What non-toxin related diseases does Staph aureus cause?
1) Pneumonia secondary to viral URTI
2) Septic arthritis
3) Deep infections in any tissue → abscesses
4) SSTIs (eg. folliculitis, impetigo
5) Osteomyelitis (#1)
6) Infective endocarditis (rapid onset in healthy native heart valves/IV drug use)
How does MRSA develop resistance to ß-lactams?
Altered PBP2a (mecA gene) → ↓ affinity for ß-lactams
What antibiotics are used in a MSSA infection?
Cloxacillin (penicillinase-resistant penicillin)
or Erythromycin/clindamycin in penicillin-allergic
What antibiotics are used in an MRSA infection?
1) Vancomycin (empirical coverage)
2) Ceftaroline, Ceftobiprole (5th gen Cephalosporins)
How is an MRSA infection treated?
1) Drain pus and debride
2) Topical mupirocin (for SSTI)
3) Vancomycin/Ceftabiprole/Ceftaroline
How and why do we type Staph aureus infections?
To discern if it is an outbreak (multiple closely-related isolates → common source)
1) AMR profiles
2) Sequence typing (MLST, WGS)
