Gram positive cocci

• What are the three main types of Gram-positive cocci discussed in the overview?

  Staphylococci, Streptococci, and Enterococcus
• What are the general characteristics of Staphylococci?

  • Catalase-producing, gram-positive cocci
  • Spherical cells (0.5 to 1.5 µm) appear singly, in pairs, and in clusters
  • Members of the indigenous microbiota
  • Some species are causative agents of serious infectious diseases
• What is the genus name for Staphylococci derived from?

  The Greek term "staphle," meaning "bunches of grapes."
• Why can't microscopy alone differentiate Staphylococci from other Gram-positive cocci?

  Because the Gram stain can be characteristic but not definitive.
• What family do Staphylococci belong to?

  The family Staphylococcaceae.
• What are the characteristics of Staphylococci in terms of motility and spore formation?

  They are nonmotile and nonspore-forming.
• What is the appearance of Staphylococci colonies after 18 to 24 hours of incubation?

  Medium sized (4 to 8 mm), cream-colored, white, or light gold, and "buttery-looking."
• What is a rare characteristic of some strains of Staphylococci regarding their growth requirements?

  They are fastidious and require carbon dioxide, hemin, or menadione for growth.
• Which species of Staphylococcus is β-hemolytic?

  Staphylococcus aureus.
• What is the most clinically significant species of Staphylococci?

  Staphylococcus aureus.
• What diseases can Staphylococcus aureus cause?

  • Superficial skin lesions (e.g., folliculitis)
  • Deep-seated abscesses
  • Pyogenic infections (e.g., pneumonia, septic arthritis)
  • Toxin-mediated diseases (e.g., food poisoning, TSS, SSSS)
• From where can Staphylococcus aureus be recovered?

  Almost any clinical specimen.
• What is a major concern regarding Staphylococcus aureus?

  Increasing drug resistance.
• How does Staphylococcus aureus appear on different culture media?

  1. Blood agar: Clear zone of beta-hemolysis.
  2. MacConkey agar: Small pink colonies due to lactose fermentation.
  3. Mannitol salt agar: Yellow zone formation around colonies due to mannitol fermentation.
• How can Staphylococci be identified in the laboratory?

  They are gram-positive cocci predominantly in clusters and catalase positive.
• What biochemical reaction is used to differentiate Staphylococcus aureus from other Staphylococci?

  Coagulase production.
• What does the catalase enzyme do in Staphylococcus aureus?

  It degrades H2O2 into nascent oxygen and water.
• What sugars does Staphylococcus aureus ferment under aerobic conditions?

  Mannitol, sucrose, maltose, and trehalose.
• What is the significance of mannitol fermentation in Staphylococcus aureus?

  Most strains of S. aureus ferment mannitol, while others do not.
• What is the susceptibility of Staphylococcus aureus to physical and chemical agents?

  They are extremely hardy and can survive in adverse environments.
• What temperature can some strains of Staphylococcus aureus withstand?

  60°C for 30 minutes.
• How do Staphylococcus aureus strains respond to aniline dyes?

  They are very sensitive to aniline dyes.
• What is the primary reservoir for Staphylococcus aureus?

  The human naris.
• What percentage of the human population are carriers of Staphylococcus aureus?

  Nearly one-third.
• What is the incidence of nasal carriage of Staphylococcus aureus in humans?

  40-50% of humans.
• How is Staphylococcus aureus transmitted in healthcare settings?

  • Direct cross-infection from one human to another
  • Airborne transmission
  • Contact with unwashed, contaminated hands
  • Contact with inanimate objects (fomites)
• What is a major health concern regarding MRSA infections?

  They have become a major health care concern.
• What are the virulence factors of Staphylococcus aureus?

  • Enterotoxins (A, B, D)
  • Toxic Shock Syndrome Toxin-1 (TSST-1)
  • Cytolytic toxins (hemolysins and leukocidins)
  • Exfoliative toxin
  • Various enzymes (coagulase, protease, hyaluronidase, nucleases, lipase)
• What are the symptoms caused by Staphylococcal enterotoxins?

  Diarrhea and vomiting.
• How stable are Staphylococcal enterotoxins at high temperatures?

  They are stable at 100°C for 30 minutes.
• What is the role of Toxic Shock Syndrome Toxin-1 (TSST-1) in Staphylococcus aureus infections?

  It causes nearly all cases of menstruating-associated TSS.
• What is the effect of cytolytic toxins produced by Staphylococcus aureus?

  They affect and lyse red blood cells and leukocytes.
• What is the significance of α-Hemolysin produced by Staphylococcus aureus?

  It can damage platelets and macrophages and cause severe tissue damage.
• What is the role of hyaluronidase in Staphylococcus aureus pathogenicity?

  It hydrolyzes hyaluronic acid, allowing bacterial spread during infection.
• What types of infections can Staphylococcus aureus cause?

  • Suppurative infections (e.g., abscesses)
  • Toxin-mediated infections (e.g., food poisoning)
  • Skin and wound infections
• What factors determine the severity of Staphylococcus aureus infections?

  The virulence of the strain, size of the inoculum, and host's immune status.
• How do Staphylococcus aureus infections initiate?

  When a breach of the skin or mucosal barrier allows access to tissues or bloodstream.
• What is the role of the host's acute inflammatory response in Staphylococcus aureus infections?

  It leads to the proliferation and activation of polymorphonuclear cells.
• How do Staphylococcus aureus organisms resist the action of inflammatory cells?

  By producing toxins and enzymes.
• What are the common skin and wound infections caused by Staphylococcus aureus?

  • Folliculitis
  • Furuncles
  • Carbuncles
  • Bullous impetigo