Staphylococci

• What are the two most common groups of Gram-positive organisms of medical importance?

  Staphylococci and Streptococci
• What is the Gram stain result for Staphylococcus aureus?

  Gram-positive
• How are Staphylococci described in terms of their shape?

  They are cocci, which are spherical bacteria.
• What does it mean that Staphylococcus aureus is catalase-positive?

  It means it can effectively deal with oxidative defensive processes.
• Why is Staphylococcus aureus considered hardy?

  Because it can survive quite well outside the animal host.
• What is the significance of Staphylococcus aureus being a commensal organism?

  Many are normally harmless but can cause infections.
• What is a characteristic feature of Staphylococcus aureus colonies?

  They have golden colonies, hence the name "aureus."
• What does the coagulase enzyme produced by Staphylococcus aureus do?

  It converts fibrinogen to fibrin, providing protection from the immune system.
• Why is simple colonization of Staphylococcus aureus not considered an infection?

  Because it can be carried by healthy people without causing disease.
• What is the role of Protein A in Staphylococcus aureus?

  It binds to IgG, preventing opsonization and exerting an anti-phagocytic effect.
• What is the function of fibronectin-binding protein (FnBP) in Staphylococcus aureus?

  It promotes binding to mucosal cells and tissue matrices.
• What are cytolytic exotoxins, and which is the most significant in Staphylococcus aureus?

  They attack mammalian cell membranes, with Panton-Valentine Leucocidin (PVL) being the most significant.
• What is the effect of superantigen exotoxins produced by Staphylococcus aureus?

  They stimulate an enhanced T cell response, leading to toxic shock syndrome.
• What are the most common infections caused by Staphylococcus aureus?

  Localized skin infections, such as impetigo and abscesses.
• What is cellulitis, and how is it related to Staphylococcus aureus?

  It is a localized skin infection that may involve the dermis and subcutaneous fat.
• What is the clinical significance of deep infections caused by Staphylococcus aureus?

  They can be highly invasive and cause significant localized damage.
• What is septicaemia, and how is it related to Staphylococcus aureus?

  It is a serious condition often originating from skin wounds or medical devices.
• What are the symptoms of toxic shock syndrome caused by Staphylococcus aureus?

  Fever, rash, vomiting, diarrhoea, hypotension, and multi-organ involvement.
• What is scalded skin syndrome, and what causes it?

  It is caused by specific toxins leading to epithelial desquamation.
• What is the treatment approach for destructive infections caused by Staphylococcus aureus?

  Aggressive treatments including source control and antibiotics are needed.
• What is the first-line antibiotic choice for treating Staphylococcus aureus infections?

  Flucloxacillin, which is resistant to beta-lactamase.
• What is MRSA, and why is it significant in healthcare settings?

  MRSA is methicillin-resistant Staphylococcus aureus, often associated with healthcare settings and higher mortality rates.
• What is the role of coagulase-negative staphylococci (CNS) in clinical settings?

  They are part of the normal flora but can cause infections, especially in implanted devices.
• What is Staphylococcus saprophyticus, and what condition does it commonly cause?

  It is part of the normal flora of the female genital tract and can cause cystitis, especially in younger women.
• What are the key virulence factors of Staphylococcus aureus?

  • Protein A: Binds to IgG, preventing opsonization
  • Fibronectin-binding protein (FnBP): Promotes binding to mucosal cells
  • Cytolytic exotoxins: Attack mammalian cell membranes (e.g., PVL)
  • Superantigen exotoxins: Stimulate T cell response, causing toxic shock syndrome
• What are the clinical significance and infections associated with Staphylococcus aureus?

  • Infections: Localized skin infections, cellulitis, septicaemia, endocarditis, pneumonia, toxic shock syndrome, scalded skin syndrome, gastroenteritis
  • Treatment: Aggressive treatment needed for destructive infections, often with flucloxacillin
• What is the overview of coagulase-negative staphylococci (CNS)?

  • Not Staphylococcus aureus
  • Lower virulence
  • Part of normal flora, especially on skin
  • Can cause infections in implanted devices
• What is the overview of Staphylococcus saprophyticus?

  • Part of normal flora of female genital tract
  • Causes cystitis, especially in younger women
  • Sensitive to most antibiotics