Multiple Choice
A medium that inhibits the growth of organisms other than the one being studied is termed a(n)
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10. Dynamics of Microbial Growth
Reviewing the Types of Culture Media
2:25 minutesProblem 2
Textbook Question
Describe the type of hemolysis shown by the pathogen Staphylococcus aureus pictured here.
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Observe the clear zones surrounding the bacterial colonies on the blood agar plate. These clear zones indicate the breakdown of red blood cells (RBCs) around the colonies.
Recall that hemolysis on blood agar is classified into three types: alpha-hemolysis (partial hemolysis with greenish discoloration), beta-hemolysis (complete hemolysis with clear zones), and gamma-hemolysis (no hemolysis, no change in the medium).
Note that the image shows distinct, transparent clear zones around the colonies, which means the RBCs have been completely lysed in those areas.
Identify this pattern as beta-hemolysis, which is characteristic of Staphylococcus aureus due to its production of hemolysins that completely lyse red blood cells.
Conclude that the type of hemolysis shown by Staphylococcus aureus in the image is beta-hemolysis, indicated by the clear, transparent zones around the bacterial colonies on the blood agar.
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2mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Hemolysis Types on Blood Agar
Hemolysis refers to the breakdown of red blood cells by bacterial enzymes on blood agar plates. There are three main types: alpha (partial, greenish discoloration), beta (complete clearing around colonies), and gamma (no hemolysis). Identifying hemolysis type helps differentiate bacterial species.
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Beta-Hemolysis Characteristics
Beta-hemolysis is characterized by a clear, transparent zone surrounding bacterial colonies on blood agar, indicating complete lysis of red blood cells. This type of hemolysis is typical of pathogens like Staphylococcus aureus and Streptococcus pyogenes, aiding in their identification.
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Staphylococcus aureus Identification
Staphylococcus aureus is a gram-positive cocci known for producing beta-hemolysis on blood agar. Its ability to completely lyse red blood cells is a key diagnostic feature, along with other tests like coagulase positivity, helping distinguish it from other Staphylococcus species.
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