Microbiology - 010 - Hemolysis

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Some bacteria are able to break down blood cells by a process called hemolysis. To test for hemolytic activity in a strain of bacteria, simply inoculate a blood agar plate with a pure culture of the strain of interest. Blood agar plates contain mammalian blood as a nutrient source, but this also allows us to observe how a bacterium interacts with blood. Notice how an uninoculated blood agar plate is red and opaque. After incubating an inoculated blood agar plate, observe the media around the bacteria growing on it. Look for changes in the opaque, red color. If the area around the bacteria turns transparent, that strain displays complete hemolysis, also known as beta hemolysis. Such a strain would be called beta-hemolytic. Notice how the agar is completely transparent, showing objects behind the plate. If the media around the bacteria changes to a dark green color but does not become transparent, the bacteria are displaying incomplete hemolysis, or alpha hemolysis. These bacteria are alpha-hemolytic. Notice how the media is discolored, but objects behind the blood agar plate cannot be seen. Bacteria that grow on the blood agar but don’t change the appearance of the media at all are said to display gamma hemolysis and are called gamma hemolytic bacteria. Knowing what type of hemolysis a bacterial strain is capable of can be helpful in identifying several types of bacteria, especially organisms isolated from human tissue such as Streptococcus and Staphylococcus species.

Some bacteria are able to break down blood cells by a process called hemolysis. Knowing what type of hemolysis a bacterial strain is capable of can be helpful in identifying several types of bacteria, especially organisms isolated from human tissue such as Streptococcus and Staphylococcus species.

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