Staphylococcus aureus: Difference between revisions
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Staphylococcus aureus
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=== Microbiology === |
=== Microbiology === |
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* Facultative anaerobic, [[Has Gram stain::Gram-positive]] coccus |
* Facultative anaerobic, [[Has Gram stain::Gram-positive]] coccus |
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* Catalase and coagulase positive |
* [[Has catalase test::Catalase-positive]] and [[Has coagulase test::coagulase-positive]] |
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* Microscopy: groups or clusters ("cluster of grapes") |
* Microscopy: groups or clusters ("cluster of grapes") |
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* Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar |
* Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar |
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Revision as of 13:24, 10 November 2019
Background
Microbiology
- Facultative anaerobic, Gram-positive coccus
- Catalase-positive and coagulase-positive
- Microscopy: groups or clusters ("cluster of grapes")
- Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
Pathophysiology
Virulence factors
- Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
- Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL)
- Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome
- Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
- Toxic shock syndrome toxin 1 (TSST-1) is implicated in Staphylococcal toxic shock syndrome
- Exotoxins B and C cause Staphylococcal toxic shock syndrome and also food poisoning
Antibiotic resistance
- Mechanisms of resistance are myriad
- Two common ones:
- bla gene encodes penicillinase, conferring resistance to penicillin
- mecA encodes PBP2a, conferring broad beta-lactam resistance
Clinical Presentation
Colonization
- About 20-30% of people carry it in their nares
- See Staphylococcus aureus decolonization
Skin and soft tissue infections
- Boils and carbuncles
Scalded-skin syndrome
- Aka Ritter disease
- Caused by exfoliative toxin A or B
- Essentially bullous impetigo
- Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)
Bacteremia
Infective endocarditis
- Usually more acute presentation
- High mortality
- See Staphylococcus aureus endocarditis
Myriad other infections
- Osteomyelitis
- Native and prosthetic joint infections
- Pyomyositis
- Deep organ abscesses
- Surgical site infections
- Pneumonia, especially ventilator-associated or influenza-related
- Food poisoning
- Staphylococcal toxic shock syndrome
- Tampon-associated
- Post-surgical (ENT): more of historic with changes in packing
- Surgical site infections, even without obvious signs of localized infection
Management
- Duration depends on clinical syndrome
Methicillin-susceptible Staphylococcus aureus (MSSA)
- First-line: cloxacillin, then cefazolin or cephalexin (for oral)
- Others: clindamycin, fluoroquinolones, TMP-SMX, doxyxycline, erythromycin
Methicillin-resistant Staphylococcus aureus (MRSA)
- First-line: vancomycin
- Others: linezolid (if lungs) and daptomycin (if blood), but also consider TMP-SMX, ciprofloxacin, doxycycline, and clindamycin
