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