Genus Staphylococcus

• What is the shape of Staphylococcus aureus under a microscope?

  Cocci, resembling grapes
• What color does Staphylococcus aureus appear on agar?

  Yellow/golden
• What are the morphological characteristics of Staphylococcus aureus?

  • Gram +ve
  • Catalase +ve
  • Coagulase +ve
  • Beta-haemolytic
  • Non-motile
  • No spores
  • Capsule formation (sometimes)
  • Ferments mannitol, turning agar yellow
• What is the virulence factor of Staphylococcus aureus?

  Protein A
• How does Protein A contribute to Staphylococcus aureus pathogenesis?

  It prevents opsonization and phagocytosis
• What does MRSA stand for?

  Methicillin-Resistant Staphylococcus aureus
• What causes MRSA resistance to methicillin?

  Altered Penicillin Binding Protein
• What are the transmission routes for Staphylococcus aureus?

  • Hands
  • Sneezing
  • Surgical wounds
  • Contaminated foods
• What are the predisposing factors for Staphylococcus aureus infection?

  • Surgery/wounds
  • IV drug abuse
  • Cystic fibrosis
  • Severe neutropenia
  • Chronic granulomatous disease
  • Foreign bodies (e.g., tampons, surgical packings)
• What are the diseases caused by Staphylococcus aureus and their symptoms?

  • Gastroenteritis: nausea, abdominal pain, vomiting, diarrhea
  • Acute infective endocarditis: fever, malaise, heart murmur
  • Toxic shock syndrome: fever, hypotension, rash, multi-organ failure
  • Osteomyelitis: bone pain, fever, tissue swelling
  • Pneumonia: productive cough, rapid onset, high fatality
  • Abscesses & mastitis: tenderness, redness, swelling
  • Impetigo & scalded skin syndrome: skin peeling
  • Surgical infections: fever, cellulitis, abscess
• What causes gastroenteritis symptoms in Staphylococcus aureus infections?

  Toxin ingested preformed in food
• How quickly do symptoms of gastroenteritis appear after ingestion?

  2-6 hours
• What are the pathogenicity factors in acute infective endocarditis caused by Staphylococcus aureus?

  Fibrin platelet mesh and cytolytic toxins
• What is the common cause of osteomyelitis?

  Staphylococcus aureus
• What are the symptoms of osteomyelitis?

  Bone pain, fever, tissue swelling
• What is the pathogenicity factor in pneumonia caused by Staphylococcus aureus?

  Cytolysin toxin and coagulase
• What are the symptoms of toxic shock syndrome?

  Fever, hypotension, rash, multi-organ failure
• What is the treatment for gastroenteritis caused by Staphylococcus aureus?

  Self-limiting
• What antibiotics are used to treat Staphylococcus aureus infections?

  Nafcillin/Oxacillin and Vancomycin
• What is the treatment for MRSA infections?

  Vancomycin
• What is the treatment for Vancomycin-resistant Staphylococcus aureus?

  Quinupristin/Dalfopristin
• What are the general features of Staphylococcus epidermidis and Staphylococcus saprophyticus?

  • Gram +ve
  • Catalase +ve
  • Urease +ve
  • Coagulase -ve
  • Non-motile
  • No spores
  • Facultative anaerobes
  • White colonies
  • Gamma-haemolysis or no haemolysis
• What is a common clinical manifestation of Staphylococcus epidermidis?

  Endocarditis in artificial heart valves
• What is the treatment for Staphylococcus epidermidis infections?

  Vancomycin
• What is Staphylococcus saprophyticus known for?

  Common cause of UTI in females
• What specimens are used for microbiological diagnosis of Staphylococcus infections?

  • Pus
  • Blood
  • Urine
  • Wound secretion
  • Throat swabs
• What is the procedure for Gram staining in microscopy?

  1. Prepare a smear
  2. Heat-fix the smear
  3. Apply crystal violet
  4. Add iodide to bind crystal violet
  5. Decolorize with alcohol or acetone
  6. Counterstain with safranin or carbol fuchsin
• What does Mannitol Salt Agar indicate for Staphylococcus aureus?

  Yellow colonies due to pH decrease
• What does the catalase test distinguish between?

  Staphylococci (+ve) and streptococci (-ve)
• What does the coagulase test distinguish between?

  1. aureus and S. epidermidis/saprophyticus
• What does the novobiocin test distinguish between?

  1. epidermidis and S. saprophyticus