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What is the purpose of the Bile Esculin Test?
What is the purpose of the Bile Esculin Test?
- To measure the pH of a culture medium
- To identify bacteria that can hydrolyze esculin in the presence of bile (correct)
- To determine the antibiotic susceptibility of bacteria
- To count colonies of bacteria
What types of bacteria are typically identified using 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.
All bacteria can hydrolyze esculin in the presence of bile.
False (B)
What is esculin?
What is esculin?
What color change indicates a positive result in the Bile Esculin Test?
What color change indicates a positive result in the Bile Esculin Test?
What is considered a positive result in the Bile Esculin Test?
What is considered a positive result in the Bile Esculin Test?
What ingredient in the Bile Esculin agar medium inhibits Gram-positive bacteria?
What ingredient in the Bile Esculin agar medium inhibits Gram-positive bacteria?
Organisms that hydrolyze esculin release __________ into the medium.
Organisms that hydrolyze esculin release __________ into the medium.
Which of the following results indicates a positive Bile Esculin Test?
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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