What is Hemolysis?
Hemolysis is the lysis or destruction of red blood cells.
How do we test for hemolysis?
Some organisms release an enzyme called hemolysins that cause hemolysis.
Isolates can be grown on a specific agar called BAP, or "Blood Agar Plates." Commonly used is SBA, "Sheep's Blood Agar." These growth mediums contain 5% sheep's blood and can be used to test hemolysis. Pig or goat blood could also be used.
The following protocol from a University of New Hampshire lab manual can be followed:
Label the BAP plate and divide it into a maximum of four parts if testing multiple isolates. Ensure there is enough room between isolates to observe the results.
Flame an inoculating loop until orange, let it cool, and take a sample of the isolate with the loop. Streak it onto the plate, covering most of the area designated for that isolate without crossing the dividing line.
Incubate at 26°C for 24-48 hours.
How are the results interpreted?
Three different results can occur: beta hemolysis, alpha hemolysis, and gamma hemolysis.
Beta: This is complete hemolysis. This can present as clear or transparent zones surrounding the colonies.
Alpha: This is partial hemolysis. This can present as green or brown opaque zones surrounding the colonies.
Gamma: This is no hemolysis. This can present as no change in color.
Why does it matter?
Hemolysis is a destructive process that affects any organism containing erythrocytes or red blood cells. Knowing whether or not an isolate produces the enzyme that causes hemolysis is essential for safety, appropriate handling, as well as further understanding. Streptococcus pneumoniae is the common cause of strep throat or pneumonia. When grown on BAPs, this bacteria displays beta hemolysis. If it enters the bloodstream, it can cause hemolytic anemia. Many just think of strep throat and pneumonia as things that require antibiotics, but many don't understand that if that infection were to get worse or untreated, complications other than sepsis can occur.
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