ALPHA-HEMOLYTIC STREPTOCOCCI

• Streptococcus pneumoniae

  • Diplococcus organism (two cocci organisms attached to each other)
  • Coffee bean/kidney bean shape
  • Capsulated
• Streptococcus viridans/Viridans streptococci


  • Diplococcus
  • No capsule
  • Can be in chains
• The virulence mechanism of capsule as a bacterial structure is ANTI-PHAGOCYTIC AND ANTI-COMPLIMENTARY so that means the organism is not destroyed by the phagocytes and the complement system
• Streptococcus Pneumoniae is the capsulated streptococcus between Streptococcus pneumoniae and Streptococcus viridans
• Alpha-hemolysis


  Incomplete destruction of the RBCs and that will cause greenish brown discoloration to the blood agar medium brought about by the oxidation of the hemoglobin molecule or the formation of methemoglobin in the blood agar medium
• Hiss Capsular Staining


  1. Make a smear using plasma

  2. Air dry, do not heat fix

  3. Primary stain: Carbol Fuchsin

  4. Heat to steaming for 5 mins, do not wash

  5. Decolorizer: 20% copper sulfate for 5 mins

  6. Check for diplococcus surrounded by unstained area (capsule)

  
• Optochin Sensitivity Test


  • Differentiate Streptococcus pneumoniae from Streptococcus viridans
  • Optochin disc/P disc used
  • Zone of inhibition ≥14mm using 6mm disc or ≥16mm using 10mm disc = Streptococcus pneumoniae (sensitive)
  • Resistant = Streptococcus viridans

  
• Bile Solubility Test


  1. Make bacterial suspension, divide into control and test

  2. Add 5-10 drops sodium deoxycholate to test

  3. Check for clearing of turbidity after 5-10 mins

  4. (+) clearing = Streptococcus pneumoniae

  5. (-) no clearing = Streptococcus viridans

  
• Streptococcus pneumoniae has an autolytic enzyme (amidase) that gets stimulated by bile, causing lysis of the organism

  
• Screening, Presumptive, and Confirmatory Tests for Alpha-hemolytic Streptococci

  • Screening: Colonial Morphology
  • Presumptive: Hiss Capsular, Optochin Sensitivity
  • Confirmatory: Bile Solubility