Staphylococcus aureus Flashcard
Staphylococcus aureus – A Gram-positive, spherical (coccus-shaped) bacterium that forms grape-like clusters and is commonly found on human skin and mucous membranes.
What is the Gram-stain characteristic of Staphylococcus aureus?
Gram-positive cocci, purple-staining spherical bacteria
Terms in this set
Hide AnswersWhat is the Gram-stain characteristic of Staphylococcus aureus?
Gram-positive cocci, purple-staining spherical bacteria
Describe the shape and arrangement of S. aureus cells.
Spherical (0.5–1 µm), forming grape-like clusters
What type of metabolism does S. aureus have?
Facultative anaerobe—can grow with or without oxygen
Where is S. aureus commonly found as a commensal?
Skin, nasal passages, mucous membranes in ~20–30% of people
Who discovered S. aureus and when?
Sir Alexander Ogston in 1880, from surgical abscess pus
What is coagulase and why is it significant?
Enzyme converting fibrinogen to fibrin; helps S. aureus evade immune system
Name key virulence factors produced by S. aureus.
Adhesins, coagulase, toxins (alpha, beta, delta, enterotoxins, TSST‑1, PVL), enzymes (hyaluronidase, DNase)
What is MRSA?
Methicillin-resistant Staphylococcus aureus, resistant strain emerged in 1960s
What diseases can S. aureus cause?
Skin infections, pneumonia, osteomyelitis, endocarditis, sepsis, toxic shock, food poisoning
What is TSST‑1?
Superantigen causing toxic shock syndrome by massive cytokine release
What is PVL?
Panton–Valentine leukocidin; destroys leukocytes, linked to necrotic pneumonia
Describe beta-toxin.
Sphingomyelinase C; lyses red and white blood cells; active at 10 °C
Describe delta-toxin.
Amphipathic peptide; cytolytic, pro-inflammatory, chemoattractant; heat stable
Why is staphyloxanthin important?
Golden pigment; antioxidant that protects against reactive oxygen species
What role does Protein A play?
Binds IgG Fc region; prevents opsonization and phagocytosis
How is biofilm formation relevant?
Produces glycocalyx slime; protects against antibiotics and immune attack
What laboratory tests diagnose S. aureus?
Gram stain, catalase+, coagulase+, mannitol fermentation, DNase test
How does S. aureus cause food poisoning?
Produces enterotoxins; symptoms appear within 30 min–8 hrs
What is antibiotic resistance mechanism in S. aureus?
β-lactamase and mec operon (SCCmec) confer penicillin and methicillin resistance
How to prevent S. aureus transmission?
Hand hygiene, wound care, cleaning surfaces, PPE use in healthcare
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