Staphylococcus aureus: Difference between revisions

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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

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

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)

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)

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

Choice of antibiotic depends on susceptibility testing, and duration depends on clinical syndrome

First-line: benzylpenicillin 2 million units IV every 4 hours, or 4 million units IV every 4 hours

First-line: vancomycin
Others: linezolid (if lungs) and daptomycin (if blood), but also consider TMP-SMX, ciprofloxacin, doxycycline, and clindamycin

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 ===Microbiology===
-*Facultative anaerobic, [[Stain::Gram-positive]] [[Cellular shape::coccus]]
+*Facultative anaerobic, [[Stain::Gram-positive]] [[Shape::coccus]]
 *Catalase-[[Catalase::positive]] and coagulase-[[Coagulase::positive]]
 *Microscopy: groups or clusters ("cluster of grapes")
@@ Line 53: / Line 53: @@
 *See [[Staphylococcus aureus endocarditis]]
-===Other Syndromes===
+===Other Infectious Syndromes===
 *[[Osteomyelitis]]
@@ Line 69: / Line 69: @@
 **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
+*Choice of antibiotic depends on susceptibility testing, and duration depends on clinical syndrome
+=== Penicillin-Susceptible ''Staphylococcus aureus'' (PSSA) ===
+* First-line: benzylpenicillin 2 million units IV every 4 hours, or 4 million units IV every 4 hours
 ===Methicillin-Susceptible ''Staphylococcus aureus'' (MSSA)===
+*First-line:
-*First-line: [[cloxacillin]], then [[cefazolin]] or [[cephalexin]] (for oral)
+**Intavenous: [[cefazolin]] preferred to [[cloxacillin]]
+**Oral: include [[cephalexin]], [[cefadroxil]], and oral [[cloxacillin]]
 *Others: [[clindamycin]], [[fluoroquinolones]], [[TMP-SMX]], [[doxyxycline]], [[erythromycin]]