Microbiology Lab 3 Bile Esculin Test
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Questions and Answers

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?

    Group D Streptococci and Enterococci

    All bacteria can hydrolyze esculin in the presence of bile.

    False

    What is esculin?

    <p>A glycoside composed of glucose and esculetin</p> Signup and view all the answers

    What color change indicates a positive result in the Bile Esculin Test?

    <p>Dark brown to black</p> Signup and view all the answers

    What is considered a positive result in the Bile Esculin Test?

    <p>More than half of the slant darkened</p> Signup and view all the answers

    What ingredient in the Bile Esculin agar medium inhibits Gram-positive bacteria?

    <p>Bile</p> Signup and view all the answers

    Organisms that hydrolyze esculin release __________ into the medium.

    <p>esculetin</p> Signup and view all the answers

    Which of the following results indicates a positive Bile Esculin Test?

    <p>S. bovis = Positive (Black)</p> Signup and view all the answers

    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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    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.

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