BETA-HEMOLYTIC STREPTOCOCCI

• Beta-hemolytic Streptococci


  • Identify microscopic morphology
  • Demonstrate and identify beta-hemolysis & colonial morphology
  • Differentiate Group A from Group B beta hemolytic Streptococci in terms of Bacitracin sensitivity
  • Perform CAMP test & demonstrate the enhanced hemolysis on BA plate

  
• Laboratory investigation


  1. Establish presence/absence of organism of interest (screening test)

  2. Presumptive test supports screening test result

  3. Confirm, isolate, and reveal identity of organism causing infection
• Streptococci are catalase negative (-) meaning they do not produce the enzyme catalase
• When H2O2 is added to a streptococci, it is distracted by such disinfectant
• Streptococci


  • Gram-positive (+) organisms that grow in chains
  • Chains should be long with 20 or more cocci
• Types of hemolysis patterns in Streptococci

  • Beta-hemolysis
  • Alpha-hemolysis
  • Gamma-hemolysis (non-pathogenic)

  
• Beta-hemolysis


  Complete destruction or lysis of the RBC, causing discoloration in the blood agar medium which is yellow

  
• Alpha-hemolysis


  Incomplete lysis of the RBC causing a brown discoloration to the blood agar medium

  
• Gamma-hemolysis


  No hemolysis or discoloration to the blood agar medium

  
• Streptococci group of organisms are also hemolytic organisms because they produce different hemolytic patterns in the blood agar medium

  
• Alpha-hemolytic Streptococci are Streptococci producing alpha-hemolysis in the blood agar medium

  
• Gamma-hemolytic Streptococci are non-pathogenic Streptococci
• Beta-hemolytic & Alpha-hemolytic Streptococci are classified/grouped according to the hemolytic pattern produced in the blood agar medium (Brown's Classification)

  
• Lancefield Classification


  More reliable classification than Brown's Classification, based on Antigenic Group Specific C Substance
• In order for one streptococcus to be identified correctly, the unique antigenic marker in the C Substance of that particular streptococcus species should be detected in the laboratory
• Brown Classification groups Streptococci according to their hemolytic pattern produced in the blood agar medium, but you cannot pinpoint one specific species

  
• Beta-hemolytic Streptococci


  • Streptococcus pyogenes
  • Streptococcus agalactiae
• Lancefield Classification is more reliable as it can identify the specific species of Streptococcus
• Lancefield Classification Groups


  • Group A
  • Group B
  • Group C
  • Group D
• Group A Streptococci (GAS)

  Streptococcus pyogenes
• Group B Streptococci


  Streptococcus agalactiae
• Group C Streptococci


  • Streptococcus equisimilis
  • Streptococcus equisinilis
  • Streptococcus equi
  • Streptococcus zooepidemicus
  • Streptococcus dysgalactiae
• For identification during practical exams, answer in complete manner since Streptococci organisms are being classified to both Lancefield and Brown's Classification
• Identification of Beta-Hemolytic Streptococci

  • Group A Beta-hemolytic Streptococci Streptococcus pyogenes
  • Group B Beta-hemolytic Streptococci Streptococcus agalactiae

  
• Investigation of Beta-Hemolytic Streptococci

  1. Microscopic morphology/Morphology evaluation

  2. Catalase Test

  3. Determine hemolytic pattern

  4. Bacitracin Disc Test

  5. CAMP Test

  
• Bacitracin sensitive


  Group A beta-hemolytic streptococci Streptococcus pyogenes
• Bacitracin resistant


  Group B beta-hemolytic streptococci Streptococcus agalactiae
• CAMP Test


  Streptococcus agalactiae presumptive test
• Streptokinase


  Thrombolytic reagent, therapeutic enzyme indicated to patients with pathologic clotting
• All group C Streptococci are beta-hemolytic streptococci except for S. dysgalactiae which can be alpha- or gamma-hemolytic

  
• Hemolytic pattern


  • Medium is Blood agar
  • Result: Beta-hemolytic

  
• Bacitracin Disc Test


  1. Only confirmatory test

  2. Medium is Blood agar

  3. Result: Bacitracin sensitive/susceptible or Bacitracin resistant

  
• Bacitracin sensitive


  • Group A beta-hemolytic streptococci Streptococcus pyogenes
  • Result: Zone of Inhibition is present
• Bacitracin resistant


  • Group B beta-hemolytic streptococci Streptococcus agalactiae
  • Result: No Zone of inhibition
• CAMP TEST (Christie, Atkins, Munch, Peterson)

  1. Streptococcus agalactiae presumptive test

  2. Result: Arrowhead hemolysis (positive)
• Microscopic Morphology


  • Gram staining: Cocci in chains
  • Establishes the presence of Streptococci organism in the sample
  • The specie is not yet known at this level
• CATALASE TEST


  1. Screening test

  2. Negative Result

  3. Supports the data in the microscopic morphology result
• During the first investigation of beta-hemolytic streptococci, you cannot differentiate or separate Group A Beta-hemolytic streptococci S. pyogenes from Group B Beta-hemolytic Streptococci S. agalactiae

  
• Both Group A and Group B beta-hemolytic streptococci appear in chains in the microscopic morphology

  
• Bacitracin Disc / Bacitracin Sensitivity Test


  1. The only confirmatory test

  2. Medium used is Blood agar medium

  3. Establish the beta-hemolytic property of the beta-hemolytic streptococci apart from the Blood Agar Medium that was already inoculated

  4. Support to the result to the first Blood Agar Medium (BAM)