Streptococcus 1

• What type of bacteria are streptococci?

  Gram-positive cocci
• How are streptococci typically arranged?

  In chains or pairs
• What does it mean that streptococci are described as "fastidious bacteria"?

  They sometimes require enriched media for growth
• Are streptococci motile or non-motile?

  Non-motile
• Do streptococci form spores?

  No, they are non-spore-forming
• What type of oxygen requirements do streptococci have?

  Facultatively anaerobic and some are capnophilic
• How many species of streptococci are there?

  More than 70 species
• How can streptococci be classified?

  • Type of hemolysis observed on blood agar
  • Serology (Lancefield Classification)
  • Biochemical reactions
• What is α-hemolysis on blood agar characterized by?

  A greenish zone forms around colonies due to partial hemolysis of erythrocytes
• What does β-hemolysis indicate on blood agar?

  A clear zone forms around colonies due to complete hemolysis of erythrocytes
• What is γ-hemolysis characterized by?


  No zone is formed, as erythrocytes are not lysed
• What is the basis of the Lancefield Classification?

  Differences in the cell wall polysaccharide among streptococci
• How many groups are there in the Lancefield Classification?

  20 groups
• Which groups of streptococci are considered groupable?

  Groups A, B, and D are more frequent; C, G, and F are less frequent
• What is another name for Group A Streptococci?

  Streptococcus pyogenes
• What type of colonies does S. pyogenes produce on blood agar?

  β-hemolytic colonies
• What is the sensitivity of S. pyogenes to bacitracin?

  1. pyogenes is bacitracin sensitive
• Where is S. pyogenes commonly found in the human body?

  As an upper respiratory tract commensal
• What are the virulence factors produced by S. pyogenes?

  • M protein: antiphagocytic factor
  • Capsule: antiphagocytic factor
  • Streptolysins: toxins that hemolyse red cells
  • Streptolysin S: oxygen-stable, non-antigenic
  • Streptolysin O: oxygen-labile, antigenic
  • Streptokinase: breaks down blood clots
  • Deoxyribonucleases
  • Hyaluronidase: facilitates spread through tissues
  • Erythrogenic toxin: causes rash in scarlet fever
• What is the commonest bacterial cause of pharyngitis?

  1. pyogenes
• What are the symptoms of pharyngitis caused by S. pyogenes?

  Fever, malaise, headache, red pharynx, throat pain, swollen lymph nodes, and purulent abscesses
• How is strep throat transmitted?

  By airborne respiratory droplets or contaminated objects
• What are the complications of untreated streptococcal throat infections?

  • Scarlet fever
  • Rheumatic fever
  • Glomerulonephritis
• What triggers the rash in scarlet fever?

  Erythrogenic toxin released by S. pyogenes
• What are the characteristics of the rash in scarlet fever?

  It begins on the chest and spreads across the body, with a strawberry red tongue
• What is rheumatic fever?

  An autoimmune condition that leads to damage of heart and joints
• What causes glomerulonephritis in streptococcal infections?

  Inflammation of the glomeruli and nephrons obstructing blood flow
• What are the clinical manifestations of skin infections caused by streptococci?

  • Cellulitis: localized inflammation and pain
  • Erysipelas: inflammation involving superficial lymphatic tissue
  • Impetigo: superficial skin infection
• What is necrotizing fasciitis?

  A rare aggressive life-threatening bacterial infection causing necrosis of skin and surrounding tissues
• What is streptococcal toxic shock syndrome (STSS)?

  A severe multisystem infection caused by group A streptococci leading to organ failure and shock
• What are the symptoms of STSS?

  Inflammation, pain, fever, chills, malaise, nausea, vomiting, diarrhea, and organ failure
• What is the lab diagnosis for pharyngitis caused by S. pyogenes?

  A throat swab
• What culture medium is used for S. pyogenes diagnosis?

  Blood agar
• What is the incubation condition for culturing S. pyogenes?

  Incubated aerobically or anaerobically for 18 hours at 37°C
• What is the purpose of rapid strep A tests?

  To quickly diagnose GAS pharyngitis
• What should be done if a rapid strep A test result is negative?

  Follow up with a throat culture
• What is the colony morphology of S. pyogenes on blood agar?

  Small, beta hemolytic, transparent, dry or mucoid, shiny colonies
• How do streptococci appear under Gram staining?

  Gram positive cocci arranged in short chains
• What test can differentiate streptococci from staphylococci?

  A catalase test
• What is the sensitivity of most S. pyogenes strains to bacitracin?

  Most strains are sensitive to bacitracin