Biochemical Tests for Enterobacteriaceae Identification
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Questions and Answers

What indicates a positive result in the citrate utilization test?

  • Turns orange during incubation
  • Changes from green to blue (correct)
  • Remains green in color
  • Develops black precipitate

    • Which of the following components is NOT found in the urea broth?

  • Yeast extract
  • Phenol red indicator
  • Monopotassium phosphate
  • Sodium chloride (correct)

    • What is the incubation temperature range for the urea hydrolysis test?

  • 35°C to 37°C (correct)
  • 20°C to 25°C
  • 30°C to 32°C
  • 40°C to 42°C

    • What does a yellow color in the Triple Sugar Iron Agar test indicate?

    <p>Fermentation of glucose</p> Signup and view all the answers

    What should NOT be done when inoculating Christensen’s Urea Agar?

    <p>Stab the butt of the agar</p> Signup and view all the answers

    Which purpose does the Triple Sugar Iron Agar test serve?

    <p>Testing fermentation of carbohydrates</p> Signup and view all the answers

    What do you observe after 6 hours of incubation in the urea hydrolysis test if the result is urease positive?

    <p>The slant turns pink</p> Signup and view all the answers

    What ingredient in TSI agar serves as the pH indicator?

    <p>Phenol red</p> Signup and view all the answers

    What is the purpose of the Indole Test?

    <p>To assess the capability to produce indole</p> Signup and view all the answers

    Which reagent is used in the Indole Test to detect indole production?

    <p>Kovac’s reagent</p> Signup and view all the answers

    What are the end products being tested in the Methyl Red Test?

    <p>Acid end products from glucose fermentation</p> Signup and view all the answers

    In the Voges Proskauer Test, which substance indicates a positive result?

    <p>Red color development</p> Signup and view all the answers

    Which medium contains sodium citrate as the carbon source for the Citrate Test?

    <p>Simmon’s Citrate Agar</p> Signup and view all the answers

    After incubating glucose broth for the Methyl Red and Voges Proskauer Tests, what is the next step for the Methyl Red Test?

    <p>Add a few drops of Methyl Red indicator</p> Signup and view all the answers

    Which of the following descriptions correctly summarizes a negative result for the Indole Test?

    <p>Yellow color with no color change</p> Signup and view all the answers

    Signup and view all the answers

    What characteristic odor is associated with P.aeruginosa colonies on bacteriological media?

    <p>Grape-like odor</p> Signup and view all the answers

    Which of the following biochemical tests would yield a negative result for P.aeruginosa?

    <p>Indole test</p> Signup and view all the answers

    What color are the colonies of P.aeruginosa on MacConkey agar?

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

    Which test is NOT used for identifying P.aeruginosa?

    <p>Sulfur reduction test</p> Signup and view all the answers

    What is the primary function of TCBS agar in the identification of Vibrio cholerae?

    <p>For selective isolation of Vibrios</p> Signup and view all the answers

    Which of the following carbohydrates can V.cholerae ferment?

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

    What characteristic arrangement does the Neisseria species display under the microscope?

    <p>Pairs of diplococci</p> Signup and view all the answers

    What type of motility is exhibited by Vibrios?

    <p>Flagellar motility</p> Signup and view all the answers

    What is the significance of the 'cholera red reaction' in identifying V.cholerae?

    <p>Indicates acid production</p> Signup and view all the answers

    Which medium is suitable for the growth of Neisseria species?

    <p>Thayer-Martin selective agar</p> Signup and view all the answers

    Which of the following biochemical tests is N.gonorrhoeae positive for?

    <p>Oxidation of glucose</p> Signup and view all the answers

    What additional gas is necessary for enhancing the growth of Neisseria?

    <p>Carbon dioxide</p> Signup and view all the answers

    What is a positive result indicated by in Kovac's oxidase test?

    <p>Change to a dark blue or purple color</p> Signup and view all the answers

    Which substances are N.meningitides positive for in terms of carbohydrate utilization?

    <p>Ferment glucose and maltose</p> Signup and view all the answers

    What precaution should be taken when performing tests on Neisseria species?

    <p>Use white candles only</p> Signup and view all the answers

    From which type of specimen is N.gonorrhoeae commonly isolated?

    <p>Vaginal and cervical specimens</p> Signup and view all the answers

    Study Notes

    Biochemical Tests for Enterobacteriaceae Identification

    • IMViC Tests: A series of tests differentiating various Enterobacteriaceae species. These tests include Indole, Methyl Red, Voges-Proskauer, and Citrate tests.

    Indole Test

    • Purpose: Determines a bacterium's ability to produce indole from tryptophan.
    • Media/Reagents: Tryptone broth (contains tryptophan); Kovac's reagent (detects indole).
    • Procedure: Inoculate tryptophan broth, incubate, add Kovac's reagent.
    • Positive Result: Red color at the top of the tube indicates indole production.
    • Negative Result: No color change.

    Methyl Red (MR) and Voges-Proskauer (VP) Tests

    • Purpose: Differentiates species by determining the types of end products created during glucose fermentation.
      • Methyl Red (MR): tests for acid end products.
      • Voges-Proskauer (VP): tests for acetoin production.
    • Media/Reagents: Glucose broth; Methyl Red indicator; Voges-Proskauer reagent A (alpha-naphthol and ethanol); Voges-Proskauer reagent B (potassium hydroxide and water).
    • Procedure: Inoculate glucose broth tubes, incubate, add MR indicator to one tube and VP reagents to the other.
    • Results: Observe color changes in tubes for both tests - red color for MR, and red color to a deep pink for VP.
    • Example: P. aeruginosa is negative for both MR and VP tests.

    Citrate Test

    • Purpose: Determines a bacterium's ability to use citrate as its sole carbon source and ammonium as its sole nitrogen source.
    • Media/Reagents: Simmons' Citrate Agar (contains sodium citrate, ammonium ion, and bromothymol blue pH indicator).
    • Procedure: Inoculate slant, incubate, observe color change.
    • Positive Result: Blue color change along the slant.
    • Negative Result: Remains green.
    • Example: P. aeruginosa is positive for Citrate test.

    Urea Hydrolysis Test (Urease Test)

    • Purpose: Determines a bacterium's ability to hydrolyze urea to ammonia using the enzyme urease.
    • Media/Reagents: Urea broth (contains urea and phenol red indicator).
    • Procedure: Inoculate urea broth. Incubate and observe for color change.
    • Positive Result: Turns pink (or other color) within a few hours - indicates an acidic product is formed.
    • Negative Result: Slant remains same color (indicating no enzyme activity was observed).
    • Example: Vibrio cholerae is negative for Urease test.

    Triple Sugar Iron Agar (TSIA) Test

    • Purpose: Tests carbohydrate fermentation patterns and hydrogen sulfide production.
    • Media: TSIA agar (contains glucose, lactose, sucrose, and phenol red indicator).
    • Procedure: Inoculate a TSIA tube, incubate, observe for changes in pH and gas production.
    • Possible Results: Interpret based on changes in color (yellow, red, etc.) and the presence or absence of gas bubbles in the tube, as well as production of hydrogen sulfide.

    Additional Bacterial Identification Tests

    • **Pseudomonas aeruginosa: **

      • Characteristics: Gram-negative, lactose non-fermenting rod, catalase and oxidase positive, motile, produces pyocyanin (a water-soluble pigment), characteristic "grape-like" or "fresh-tortilla" odor.
      • Identification methods: growth on Cetrimide Agar, growth at 42°C, oxidase test, citrate test, OF glucose, arginine dihydrolase tests; negative for Indole, VP, and MR tests. Colonies on nutrient agar may be green (pyocyanin production).
      • P. aeruginosa does not ferment lactose on MacConkey agar (colorless colonies).

    • **Vibrio cholerae: **

      • Characteristics: Gram-negative, curved rods (comma-shaped), catalase and oxidase positive, motile, fermentative (acid production, no gas), ferments glucose, mannitol, maltose, mannose, and sucrose; does not ferment inositol, arabinose, or lactose; indole positive, nitrates reduced to nitrites. Produces colonies surrounded by a green zone on blood agar. Identifies using TCBS agar (Thiosulfate Citrate Bile Salts Sucrose) which is selective for Vibrio species
      • Identification: TCBS agar: sucrose fermentation (large yellow colonies).

    • Neisseria:

      • Characteristics: Gram-negative diplococci, coffee bean-shaped, non-motile, non-spore-forming (capsule can be present), aerobe (5% CO2 may enhance growth), often found in pairs.
      • Identification Methods: Gram stain, oxidase test, carbohydrate utilization (glucose fermentation, but not maltose or lactose), often using chocolate agar or Thayer-Martin agar; grown on modified Thayer-Martin (MTM) agar.
      • N. gonorrhoeae identification: use of carbohydrate fermentation tests (glucose positive, but not maltose or sucrose).
      • N. meningitides identification: differences from other Neisseria via acid end-products of glucose and maltose; negative for sucrose and lactose.
      • Use special media (modified Thayer-Martin – MTM) and Candle jars for optimal growth of Neisseria; avoid nichrome wire loops for tests.

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    Description

    This quiz covers the biochemical tests used for identifying different species of Enterobacteriaceae, including IMViC tests such as Indole, Methyl Red, and Voges-Proskauer tests. Understand the purpose, procedures, and interpretations of test results to enhance your microbiological skills.

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