streptococcal

• Streptococcaceae


  Catalase negative, gram-positive cocci
• Streptococcaceae


  • Arranged in pairs or chains (due to single plane of division)
• Streptococcus pyogenes


  Belongs to Group A-Lancefield grouping
• Streptococcus agalactiae


  Belongs to Group B-Lancefield grouping
• Enterococci


  Belongs to Group D-Lancefield grouping
• Virulence factors of Streptococcus pyogenes

  • Cell wall antigens: Lipoteichoic acid, C-carbohydrate antigens, M protein, Capsule
  • Toxins – Streptolysin O & Streptolysin S, Streptococcal Pyrogenic Exotoxin, Streptokinase, Streptodornase (DNase), Hyaluronidase
• Transmission of S.pyogenes infection

  Respiratory droplets
• Specimen collection and transport

  Depends on the site of the infection
• Direct smear microscopy


  • Pus cells with gram-positive cocci in short chains
• Blood agar culture


  • Pinpoint colony with a wide zone of β-hemolysis
• Selective media for Streptococcal pyogenes

  • Crystal violet blood agar
• Culture smear


  • Gram-positive cocci in short chains
• Biochemical identification


  • Catalase negative, bacitracin sensitive, CAMP test negative
• Serology


  ASO antibodies and anti-DNase B antibodies
• Group B Streptococci (S. agalactiae)


  Pathogenesis and Clinical Manifestations
• Approximately 5–40% of women - vaginal or rectal carriers of group B Streptococcus (GBS)
• GBS infection - common in neonates and pregnancy
• GBS is recognized as a major cause of neonatal sepsis and meningitis
• Common infections caused by GBS

  • Cellulitis and soft tissue infections (including infected diabetic skin ulcers)
  • UTI
  • Pneumonia
  • Endocarditis
• Bacitracin sensitivity test


  • S.pyogens is sensitive, S.agalactiae is Resistant
• CAMP test


  • S.pyogens is Negative, S.agalactiae is Positive
• Hemolysis on blood agar

  • S.pyogenes produces β-hemolysis, Enterococci produces Non or γ-hemolytic
• Viridans streptococci


  Found as normal flora in oral cavity