Staphylococcus aureus

• What type of bacteria are Staphylococcus and Micrococcus?

  Gram positive cocci
• How are Staphylococcus bacteria arranged?

  In irregular grape-like clusters

  
• Where are Staphylococcus bacteria commonly found in humans?

  On skin and mucous membranes as commensals
• What enzyme do Staphylococcus bacteria produce?

  Catalase
• How are Staphylococcus clinically grouped?

  1. Coagulase positive Staphylococci

  • Staphylococcus aureus

  1. Coagulase negative Staphylococci

  • S. epidermidis
  • S. saprophyticus
• What is the characteristic of Staphylococcus aureus?

  Produces coagulase and catalase enzymes
• What does Staphylococcus aureus ferment?

  Mannitol
• How can Staphylococcus aureus be transmitted?

  By direct contact or fomites
• What are the mechanisms of pathogenicity for Staphylococcus aureus?

  • Surface proteins for adherence - –protein A binds the Fc portion of immunoglobulin - prevent opsonization
  • Teichoic acid causing septic shock
  • Capsule for antiphagocytic properties
  • Produces various enzymes (e.g., coagulase, haemolysins) that facilitate invasiveness
  • Forms biofilms and small-colony variants
• What is the role of protein A in Staphylococcus aureus?

  Prevents opsonization by binding the Fc portion of immunoglobulin
• What does coagulase do in Staphylococcus aureus?

  Clots plasma and interferes with phagocytosis, facilitates spread in tissues
• What do haemolysins do?

  Lyse red blood cells
• What is the function of leukocidin?

  Kills leucocytes
• What does fibrinolysin digest?

  Fibrin
• What does lipase break down?

  Fat
• What does hyaluronidase facilitate?

  Spread in tissues by destroying hyaluronic acid
• What is the role of beta-lactamase in Staphylococcus aureus?

  Associated with antibiotic resistance
• What are small-colony variants (SCVs)?

  Contribute to persistent and recurrent infection
• What are enterotoxins responsible for?

  Causing food poisoning
• What does toxic shock syndrome toxin cause?

  Toxic shock syndrome - TSS (Shock, rash, desquamation of skin)
• What do epidermolytic toxins A and B cause?

  Staphylococcal Scalded Skin Syndrome - SSSS (Generalized peeling of the skin)
• What are the clinical features of Staphylococcus aureus infections?

  1. Pyogenic diseases

  • Local lesions (impetigo, boils)
  • Deep infections (septicemia, endocarditis)

  1. Toxin-mediated diseases

  • Food poisoning (gastroenteritis)
  • Toxic shock syndrome
  • Staphylococcal Scalded Skin Syndrome (SSSS)
• What causes food poisoning from Staphylococcus aureus?

  Ingestion of preformed toxin in food
• What are the symptoms of food poisoning caused by Staphylococcus aureus?

  Vomiting and watery non-bloody diarrhea
• How long do symptoms of food poisoning last?

  Resolve within 24 hours
• What characterizes toxic shock syndrome?

  Fever, erythematous skin rash, desquamation of the palms of the hands and the soles of the feet and shock
• What is Staphylococcal Scalded Skin Syndrome (SSSS) characterized by?

  Fever and large erythematous rash
• Who is most commonly affected by SSSS?

  Children, neonates, and renal failure adults
• What specimens are used for laboratory diagnosis of Staphylococcus aureus?

  • Pus and swabs from infected sites
  • Sputum
  • Blood
  • Nasal swabs from carriers
• What microscopy technique is used for Staphylococcus diagnosis?

  Gram stain to observe cocci in clusters
• What culture media is used for Staphylococcus aureus?

  • Blood agar
  • Mannitol salt agar (selective and differential)
• What is the incubation temperature and time for Staphylococcus culture?

  37°C for 12-18 hours in air
• What is the colonial morphology of Staphylococcus aureus on blood agar?

  Golden-yellow and beta-haemolytic
• What color are colonies of Staphylococcus aureus on mannitol salt agar?

  Yellow
• How is Staphylococcus aureus differentiated from Streptococcus?

  By catalase test (catalase positive)
• How is Staphylococcus aureus differentiated from other Staphylococcus species?

  By coagulase test (coagulase positive)
• What is the resistance profile of most Staphylococcus aureus strains?

  Resistant to penicillin
• What is MRSA(methicillin resistant S. aureus) resistant to?

  Methicillin and related penicillins
• How is MRSA treated?

  With vancomycin
• What are VRSA and VISA resistant to?

  Vancomycin and related antibiotics