Questions and Answers
What is the purpose of the Bile Esculin Test?
What types of bacteria are typically identified using the Bile Esculin Test?
Group D Streptococci and Enterococci
All bacteria can hydrolyze esculin in the presence of bile.
False
What is esculin?
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What color change indicates a positive result in the Bile Esculin Test?
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What is considered a positive result in the Bile Esculin Test?
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What ingredient in the Bile Esculin agar medium inhibits Gram-positive bacteria?
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Organisms that hydrolyze esculin release __________ into the medium.
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Which of the following results indicates a positive Bile Esculin Test?
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Study Notes
Bile Esculin Test Overview
- Purpose: Identifies bacteria capable of hydrolyzing esculin in bile presence, crucial for detecting group D Streptococci and Enterococci.
- Important genres: Enterococcus faecalis, Enterococcus faecium, and Streptococcus bovis are notable examples, all of which yield positive results.
Mechanism of the Test
- Based on the ability of certain bacteria, primarily group D Streptococcus and Enterococcus, to hydrolyze esculin in bile.
- Esculin, a glycoside composed of glucose and esculetin, is hydrolyzed under acidic conditions.
Reaction Process
- Bacteria that split esculin release esculetin into the medium.
- Free esculetin reacts with ferric citrate, forming a dark brown to black phenolic iron complex.
Agar Slant Characteristics
- A bile-esculin positive result is indicated by an agar slant darkened more than half after 48 hours of incubation.
- If less than half of the slant darkens, the result is considered negative.
Composition of Bile Esculin Agar Medium
- Ingredients include:
- Peptone: Provides supportive nutrients.
- Bile: Inhibits most gram-positive bacteria, allowing selective growth of certain Streptococcus and Enterococcus species.
- Esculin: Acts as a supportive nutrient.
- Ferric citrate: Serves as a color indicator for the test.
Test Interpretation
- Positive result: Blackening of more than half of the slant within 24-48 hours indicates esculin hydrolysis.
- Negative result: No blackening indicates a lack of esculin hydrolysis.
- Group D, H, and K Streptococcus, as well as Enterococcus species, will show positivity within 48 hours.
Specific Results
- Enterococcus faecalis: Positive (Black)
- Streptococcus bovis: Positive (Black)
- Streptococcus pyogenes: Negative (No Black)
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Description
Explore the Bile Esculin Test through these flashcards. This lab focuses on identifying bacteria that can hydrolyze esculin in the presence of bile, crucial for recognizing group D Streptococci and Enterococci. Perfect for microbiology students aiming to deepen their understanding of bacterial identification.
