BETA-HEMOLYTIC STREPTOCOCCI

Cards (47)

  • 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)