Staphylococcus aureus: Difference between revisions
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Staphylococcus aureus
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| + | ==Background== |
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| − | = Staphylococcus aureus = |
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| + | ===Microbiology=== |
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| + | *Facultative anaerobic, [[Stain::Gram-positive]] [[Shape::coccus]] |
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| − | == Microbiology == |
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| + | *Catalase-[[Catalase::positive]] and coagulase-[[Coagulase::positive]] |
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| + | *Microscopy: groups or clusters ("cluster of grapes") |
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| + | *Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar |
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| + | ===Pathophysiology=== |
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| − | * Facultative anaerobic, Gram-positive coccus |
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| + | ====Virulence Factors==== |
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| − | * Microscopy: groups or clusters ("cluster of grapes") |
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| − | * Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar |
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| + | *Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells) |
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| − | == Pathophysiology == |
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| + | *Membrane-damaging toxins (hemolysins), including Panton-Valentine leukocidin (PVL) |
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| + | *Exfoliative toxins (A and B) which disrupt the junction between epidermal cells, causing scalded skin syndrome |
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| + | *Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines |
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| + | **Toxic shock syndrome toxin 1 (TSST-1) is implicated in [[TSS|Staphylococcal toxic shock syndrome]] |
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| + | **Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning |
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| + | ====Antibiotic Resistance==== |
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| − | === Virulence factors === |
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| + | *Mechanisms of resistance are myriad |
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| − | * Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells) |
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| + | *Common ones: |
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| − | * Membrane-damaging (hemolytic) toxins |
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| + | **''bla'' gene encodes penicillinase, conferring resistance to penicillin |
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| − | * Exfoliative toxins (A and B) which disrupt the junction between epidermal cells |
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| + | **''mecA'' encodes PBP2a, conferring broad β-lactam resistance (MRSA) |
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| − | * Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines |
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| + | **''vanA'' on a plasmid confers [[vancomycin]] resistance (VRSA) |
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| − | == |
+ | ==Clinical Manifestations== |
| + | ===Colonization=== |
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| + | *About 20-30% of people carry it in their nares |
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| − | === Skin and soft tissue infections === |
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| + | *See [[Staphylococcus aureus decolonization]] |
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| + | ===Skin and Soft Tissue Infections=== |
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| − | * Boils and carbuncles |
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| + | *Boils and carbuncles |
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| − | === Scalded-skin syndrome === |
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| + | *Cellulitis, usually purulent |
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| + | ===Scalded-Skin Syndrome=== |
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| − | * Aka Ritter disease |
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| − | * Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin) |
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| + | *Aka Ritter disease |
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| − | === Bacteremia === |
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| + | *Caused by exfoliative toxin A or B |
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| + | *Essentially bullous impetigo |
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| + | *Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin) |
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| + | ===Bacteremia=== |
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| − | * See [''Staphylococcus aureus'' bacteremia](Staphylococcus aureus bacteremia.md) |
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| + | *See [[Staphylococcus aureus bacteremia]] |
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| − | === Infective endocarditis === |
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| + | ===Infective Endocarditis=== |
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| − | * Usually more acute presentation |
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| − | * High mortality |
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| + | *Usually more acute presentation |
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| − | === Myriad other infections === |
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| + | *High mortality |
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| + | *See [[Staphylococcus aureus endocarditis]] |
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| + | ===Other Infectious Syndromes=== |
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| − | * Osteomyelitis |
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| − | * Native and prosthetic joint infections |
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| − | * Pyomyositis |
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| − | * Deep organ abscesses |
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| − | * Surgical site infections |
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| − | * Pneumonia, especially ventilator-associated or influenza-related |
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| + | *[[Osteomyelitis]] |
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| − | === Superantigen-related syndromes === |
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| + | *[[Septic arthritis|Native]] and [[prosthetic joint infection]] |
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| + | *[[Pyomyositis]] |
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| + | *Deep organ [[abscess]] |
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| + | *[[Surgical site infection]] |
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| + | *[[Pneumonia]], especially ventilator-associated or influenza-related |
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| + | ===Superantigen-Related Syndromes=== |
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| − | * Food poisoning |
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| − | * Staphylococcal toxic-shock syndrome |
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| + | *[[Food poisoning]] |
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| − | == Management == |
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| + | *[[Staphylococcal toxic shock syndrome]] |
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| + | **Classically tampon-associated |
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| + | **Post-surgical (ENT): more of historic with changes in packing |
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| + | **Surgical site infections, even without obvious signs of localized infection |
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| − | === |
+ | === ''Staphylococcus''-Associated Glomerulonephritis === |
| + | * Occurs ''during'' acute infection |
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| − | * First-line: cloxacillin, then cefazolin or cephalexin |
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| + | * See also [[Staphylococcus-associated glomerulonephritis]] |
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| − | * Others: clindamycin, fluoroquinolones, Septra, doxyxycline, erythromycin |
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| + | ==Management== |
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| − | === Methicillin-resistant ''Staphylococcus aureus'' (MRSA) === |
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| + | *Duration depends on clinical syndrome |
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| − | * First-line: vancomycin |
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| + | |||
| − | * Others: linezolid (if lungs) and daptomycin (if blood), but also consider Septra, ciprofloxacin, doxycycline, and clindamycin |
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| + | ===Methicillin-Susceptible ''Staphylococcus aureus'' (MSSA)=== |
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| + | |||
| + | *First-line: [[cloxacillin]], then [[cefazolin]] or [[cephalexin]] (for oral) |
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| + | *Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]] |
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| + | |||
| + | ===Methicillin-Resistant ''Staphylococcus aureus'' (MRSA)=== |
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| + | |||
| + | *First-line: [[vancomycin]] |
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| + | *Others: [[linezolid]] (if lungs) and [[daptomycin]] (if blood), but also consider [[TMP-SMX]], [[ciprofloxacin]], [[doxycycline]], and [[clindamycin]] |
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| + | |||
| + | {{DISPLAYTITLE:''Staphylococcus aureus''}} |
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| + | [[Category:Gram-positive cocci]] |
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Latest revision as of 20:50, 21 February 2021
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
