Staphylococcus aureus: Difference between revisions

Latest revision as of 00:50, 22 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

See Staphylococcus aureus 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

@@ Line 1: / Line 1: @@
+==Background==
-= Staphylococcus aureus =
+===Microbiology===
+*Facultative anaerobic, [[Stain::Gram-positive]] [[Shape::coccus]]
-== Microbiology ==
+*Catalase-[[Catalase::positive]] and coagulase-[[Coagulase::positive]]
+*Microscopy: groups or clusters ("cluster of grapes")
+*Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
+===Pathophysiology===
-* Facultative anaerobic, Gram-positive coccus
+====Virulence Factors====
-* Microscopy: groups or clusters (&quot;cluster of grapes&quot;)
-* Colony morphology: large, round, golden yellow colonies, often hemolytic on blood agar
+*Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
-== Pathophysiology ==
+*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====
-=== Virulence factors ===
+*Mechanisms of resistance are myriad
-* Surface proteins for fibrinogen and other substances (used for binding to host endothelial cells)
+*Common ones:
-* Membrane-damaging (hemolytic) toxins
+**''bla'' gene encodes penicillinase, conferring resistance to penicillin
-* Exfoliative toxins (A and B) which disrupt the junction between epidermal cells
+**''mecA'' encodes PBP2a, conferring broad β-lactam resistance (MRSA)
-* Superantigens that bind to MHC molecules and T-cell receptors, leading to release of huge amounts of cytokines
+**''vanA'' on a plasmid confers [[vancomycin]] resistance (VRSA)
-== Clinical Presentation ==
+==Clinical Manifestations==
+===Colonization===
+*About 20-30% of people carry it in their nares
-=== Skin and soft tissue infections ===
+*See [[Staphylococcus aureus decolonization]]
+===Skin and Soft Tissue Infections===
-* Boils and carbuncles
+*Boils and carbuncles
-=== Scalded-skin syndrome ===
+*Cellulitis, usually purulent
+===Scalded-Skin Syndrome===
-* Aka Ritter disease
-* Sunburn-like, bullous rash that can lead to skin loss (most common in kids with Staph infections of the nasopharynx or skin)
+*Aka Ritter disease
-=== Bacteremia ===
+*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===
-* See [''Staphylococcus aureus'' bacteremia](Staphylococcus aureus bacteremia.md)
+*See [[Staphylococcus aureus bacteremia]]
-=== Infective endocarditis ===
+===Infective Endocarditis===
-* Usually more acute presentation
-* High mortality
+*Usually more acute presentation
-=== Myriad other infections ===
+*High mortality
+*See [[Staphylococcus aureus endocarditis]]
+===Other Infectious Syndromes===
-* Osteomyelitis
-* Native and prosthetic joint infections
-* Pyomyositis
-* Deep organ abscesses
-* Surgical site infections
-* Pneumonia, especially ventilator-associated or influenza-related
+*[[Osteomyelitis]]
-=== Superantigen-related syndromes ===
+*[[Septic arthritis|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
+*[[Food poisoning]]
-== Management ==
+*[[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
-=== Methicillin-susceptible ''Staphylococcus aureus'' (MSSA) ===
+=== ''Staphylococcus''-Associated Glomerulonephritis ===
+* Occurs ''during'' acute infection
-* First-line: cloxacillin, then cefazolin or cephalexin
+* See also [[Staphylococcus-associated glomerulonephritis]]
-* Others: clindamycin, fluoroquinolones, Septra, doxyxycline, erythromycin
+==Management==
-=== Methicillin-resistant ''Staphylococcus aureus'' (MRSA) ===
+*Duration depends on clinical syndrome
-* First-line: vancomycin
-* Others: linezolid (if lungs) and daptomycin (if blood), but also consider Septra, ciprofloxacin, doxycycline, and clindamycin
+===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]]
+{{DISPLAYTITLE:''Staphylococcus aureus''}}
+[[Category:Gram-positive cocci]]