Staphylococcus aureus: Difference between revisions

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Staphylococcus aureus
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== Microbiology ==
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==Background==
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===Microbiology===
   
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* Facultative anaerobic, [[Has Gram-stain::Gram-positive]] coccus
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*Facultative anaerobic, [[Stain::Gram-positive]] [[Shape::coccus]]
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* Catalase and coagulase positive
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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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*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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*Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
   
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== Pathophysiology ==
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===Pathophysiology===
  ⚫
====Virulence Factors====
   
  ⚫
*Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
⚫
=== Virulence factors ===
  
  ⚫
*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 [[TSS|Staphylococcal toxic shock syndrome]]
  ⚫
**Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning
   
  +
====Antibiotic Resistance====
⚫
* 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 [[TSS|Staphylococcal toxic shock syndrome]]
  
⚫
** Exotoxins B and C cause [[TSS|Staphylococcal toxic shock syndrome]] and also food poisoning
  
   
  +
*Mechanisms of resistance are myriad
⚫
== Clinical Presentation ==
  
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*Common ones:
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**''bla'' gene encodes penicillinase, conferring resistance to penicillin
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**''mecA'' encodes PBP2a, conferring broad β-lactam resistance (MRSA)
  +
**''vanA'' on a plasmid confers [[vancomycin]] resistance (VRSA)
   
  ⚫
==Clinical Manifestations==
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=== Colonization ===
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===Colonization===
   
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* About 20-30% of people carry it in their nares
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*About 20-30% of people carry it in their nares
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* See [[Staphylococcus aureus decolonization]]
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*See [[Staphylococcus aureus decolonization]]
   
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=== Skin and soft tissue infections ===
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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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*Cellulitis, usually purulent
   
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=== Scalded-skin syndrome ===
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===Scalded-Skin Syndrome===
   
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* Aka Ritter disease
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*Aka Ritter disease
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* Caused by exfoliative toxin A or B
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*Caused by exfoliative toxin A or B
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* Essentially bullous impetigo
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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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*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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===Bacteremia===
   
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* See [[Staphylococcus aureus bacteremia]]
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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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*Usually more acute presentation
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* High mortality
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*High mortality
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* See [[Staphylococcus aureus endocarditis]]
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*See [[Staphylococcus aureus endocarditis]]
   
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===Other Infectious Syndromes===
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=== Myriad other infections ===
  
   
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* Osteomyelitis
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*[[Osteomyelitis]]
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* Native and prosthetic joint infections
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*[[Septic arthritis|Native]] and [[prosthetic joint infection]]
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* Pyomyositis
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*[[Pyomyositis]]
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* Deep organ abscesses
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*Deep organ [[abscess]]
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* Surgical site infections
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*[[Surgical site infection]]
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* Pneumonia, especially ventilator-associated or influenza-related
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*[[Pneumonia]], especially ventilator-associated or influenza-related
   
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=== Superantigen-related syndromes ===
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===Superantigen-Related Syndromes===
   
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* Food poisoning
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*[[Food poisoning]]
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* Staphylococcal toxic-shock syndrome
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*[[Staphylococcal toxic shock syndrome]]
  +
**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 ===
⚫
== Management ==
  
   
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* Occurs ''during'' acute infection
⚫
* Duration depends on clinical syndrome
  
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* See also [[Staphylococcus-associated glomerulonephritis]]
   
  ⚫
==Management==
⚫
=== Methicillin-susceptible ''Staphylococcus aureus'' (MSSA) ===
  
   
  ⚫
*Duration depends on clinical syndrome
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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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===Methicillin-Susceptible ''Staphylococcus aureus'' (MSSA)===
   
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* First-line: [[vancomycin]]
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*First-line: [[cloxacillin]], then [[cefazolin]] or [[cephalexin]] (for oral)
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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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*Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]]
  +
  ⚫
===Methicillin-Resistant ''Staphylococcus aureus'' (MRSA)===
  +
  +
*First-line: [[vancomycin]]
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*Others: [[linezolid]] (if lungs) and [[daptomycin]] (if blood), but also consider [[TMP-SMX]], [[ciprofloxacin]], [[doxycycline]], and [[clindamycin]]
   
 
{{DISPLAYTITLE:''Staphylococcus aureus''}}
  
{{DISPLAYTITLE:''Staphylococcus aureus''}}

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

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

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

Other Infectious Syndromes

Superantigen-Related Syndromes

Staphylococcus-Associated Glomerulonephritis

Management

  • Duration depends on clinical syndrome

Methicillin-Susceptible Staphylococcus aureus (MSSA)

Methicillin-Resistant Staphylococcus aureus (MRSA)

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