Staphylococcus aureus
From IDWiki
Staphylococcus aureus / (Redirected from Methicillin-resistant Staphylococcus aureus)
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
- Common ones:
- bla gene encodes penicillinase, conferring resistance to penicillin
- mecA encodes PBP2a, conferring broad β-lactam resistance (MRSA)
- vanA on a plasmid confers vancomycin resistance (VRSA)
Clinical Manifestations
Colonization
- About 20-30% of people carry it in their nares
- See Staphylococcus aureus decolonization
Skin and Soft Tissue Infections
- Boils and carbuncles
- Cellulitis, usually purulent
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
Other Infectious Syndromes
- Osteomyelitis
- Native and prosthetic joint infection
- Pyomyositis
- Deep organ abscess
- Surgical site infection
- Pneumonia, especially ventilator-associated or influenza-related
Superantigen-Related Syndromes
- Food poisoning
- Staphylococcal toxic shock syndrome
- Classically tampon-associated
- Post-surgical (ENT): more of historic with changes in packing
- Surgical site infections, even without obvious signs of localized infection
Staphylococcus-Associated Glomerulonephritis
- Occurs during acute infection
- See also Staphylococcus-associated glomerulonephritis
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
