Overview and Objectives
Main Topic
Subtopic 1:
Beta-hemolytic Streptococci
1.1, 1.2, 1.3
  Subtopic 1 Summary
Subtopic 2: Alpha-hemolytic streptococci
  Activity 2
  Subtopic 2 Summary
Subtopic 3: Gamma Streptococci
3.1, 3.2
  Subtopic 3 Summary
Module Summary

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Activity 1.1: Demonstrating Hemolytic Reactions on Blood Agar


Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, and Streptococcus bovis should be plated to view different hemolytic patterns.


  1. Obtain Blood Agar medium from refrigerator. Allow medium to adjust to room temperature prior to inoculation.

  2. Using an appropriate inoculum, perform a four-quadrant streak to obtain well-isolated colonies.

  3. Incubate at 35°C in an aerobic or CO2-supplemented environment depending on the organism being cultivated.

  4. Examine after 18-24 hours. Examine the area immediately surrounding an isolated, typical colony. Hemolysis is generally visible as a thin "halo" around a hemolytic colony.

  5. In your lab report, describe alpha-, beta-, and gamma-hemolytic reactions. Identify which species produced each type of hemolysis.

Interpretation of Results

Examine plate for growth and observe morphology and hemolysis patterns of the colonies of interest. There are three main types of hemolysis:

  • Beta (β) hemolysis, where red blood cells around the colony are completely lysed or cleared

  • Alpha (α) hemolysis, where red blood cells around the colony are partially lysed or cleared giving rise to a greenish discoloration.

  • Gamma (γ) hemolysis, where red blood cells around the colony remain intact and there is no change in the medium.

Note: Additional biochemical and/or serological tests must be performed to complete identification.

View an example of hemolytic patterns.