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