Staphylococcus

• What is the morphology of Staphylococcus?

  Gram positive coccus, occurring in clusters
• What are the general features of Staphylococcus?

  Forms white to golden colonies, mainly facultative anaerobes, and is resistant to high salt concentrations
• How large are the colonies of Staphylococcus?

  Small (1-4mm) and raised
• Where is Staphylococcus commonly found in humans?

  Normal flora of nasal passages, skin, and mucous membranes
• How many species of Staphylococcus are there?

  About 40 species
• What is the main human staphylococcal pathogen?

  S. aureus
• What are the distinguishing features of S. aureus compared to other staphylococci?

  Colonies are usually golden, coagulase positive, and commonly found in the nose of humans
• What is a key diagnostic feature of S. aureus?

  Coagulase positive
• What are some virulence determinants of S. aureus?

  Surface proteins, invasins, and exotoxins
• What is an example of an invasin produced by S. aureus?

  Hyaluronidase
• What does hyaluronidase do?

  Breaks down hyaluronic acid of connective tissues
• What are cytotoxins produced by S. aureus?


  α, β, δ, γ, and Panton-Valentine toxins
• What is the function of exfoliative toxins produced by S. aureus?

  Digest the anchors that hold the epidermis to the dermis
• What are enterotoxins produced by S. aureus known for?

  They are superantigens that overstimulate the immune system
• What is Staphylococcal toxic shock syndrome toxin 1 (STSST-1)?

  Another superantigen that tends to act systemically
• How does Protein A help S. aureus evade host defenses?

  It binds antibody molecules on the wrong end, inhibiting their action
• What is the clinical manifestation of localized skin infections caused by S. aureus?

  Boils or furuncles and carbuncles
• What is scalded skin syndrome caused by?

  S. aureus strains that produce the Exfoliatin toxin
• What are the symptoms of toxic shock syndrome caused by S. aureus?

  Fever, hypotension, erythematous rash, and desquamation of the skin
• What is the most common food poisoning caused by S. aureus in the US?

  Food poisoning due to enterotoxins
• How stable are enterotoxins produced by S. aureus?

  Stable at 100 °C for 30 min and resistant to acid, base, and digestive enzymes
• What is the typical onset time for symptoms of food poisoning caused by S. aureus?

  1–6 hours after ingestion of contaminated food
• What are some other diseases caused by S. aureus?

  Bacteremia, endocarditis, osteomyelitis, and pneumonia
• What is the percentage of Staphylococcus aureus isolates from blood specimens in Ghana?

  50% of isolates

  
• How is S. aureus primarily transmitted?

  Through human-to-human contact
• What preventive measure is effective in preventing the transmission of S. aureus?

  Basic hand washing
• What is the clinical diagnosis for infections such as boils caused by S. aureus?

  Diagnosis is clinical and treatment is usually by drainage
• What laboratory tests are used for diagnosing S. aureus infections?

  Gram stain, catalase test, and coagulase test
• What is the treatment for methicillin-resistant strains of S. aureus?

  Treatment usually with vancomycin
• What is the treatment for methicillin-sensitive strains of S. aureus?

  Treatment usually with oxacillin, nafcillin, or combination therapy with gentamicin
• What disease does S. saprophyticus cause?

  Urinary tract infections
• What is the role of S. epidermidis in human health?

  Part of normal flora of skin and causes infections in immuno-compromised individuals
• What are the virulence determinants of S. aureus?

  • Surface proteins (adhesins) promote colonization
  • Invasins promote bacterial spread:
  • Hyaluronidase
  • DNases
  • Haemolysins
  • Staphylokinase
  • Leukocidin
  • Exotoxins:
  • Cytotoxins (α, β, δ, γ, Panton-Valentine)
  • Exfoliative toxins
  • Enterotoxins (A–E, G–I)
  • Staphylococcal toxic shock syndrome toxin 1 (STSST-1)
  • Evasion of host defenses (Protein A, coagulase)
• What are the diseases associated with S. aureus?

  • Localized skin infections (boils, carbuncles)
  • Postoperative wound infections
  • Toxin-related diseases:
  • Scalded skin syndrome
  • Toxic shock syndrome
  • Food poisoning
  • Other diseases (bacteremia, endocarditis, osteomyelitis, pneumonia)
• What are the laboratory and clinical diagnosis methods for S. aureus infections?

  • Clinical diagnosis through observation of symptoms
  • Laboratory diagnosis:
  • Culture of appropriate specimen
  • Gram stain
  • Catalase test
  • Coagulase test
  • Typing of strains (phage typing, multilocus sequencing)
• What are the treatment options for S. aureus infections?

  • Methicillin-resistant strains: vancomycin
  • Methicillin-sensitive strains: oxacillin, nafcillin, or combination therapy with gentamicin
• What are the transmission routes for S. aureus?

  • Human-to-human contact
  • Spread through pets
  • Preventive measures: hand washing, use of disposable gloves