Biochemical Tests in Microbiology
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Questions and Answers

What does a positive result in the biochemical test indicate?

  • Dark brown precipitate
  • Green color
  • No color change
  • Royal blue color (correct)

    • Is Escherichia coli a positive control for ammonia production tests?

    False

    What does the biochemical test aim to identify?

    Microorganisms

    The ability to use acetate as the sole source of carbon differentiates organisms such as __________ from Escherichia coli.

    <p>Shigella sp.</p> Signup and view all the answers

    What enzyme do bacteria produce to utilize acetamide?

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

    Which organism is used as a positive control in acetamide utilization tests?

    <p>Escherichia coli</p> Signup and view all the answers

    Bacitracin inhibits the synthesis of bacterial cell walls.

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

    Match the biochemical tests with their purpose:

    <p>Ammonia Production = Identify positive and negative organisms based on pH change Acetate Utilization = Differentiate organisms based on acetate usage Acetamide Utilization = Differentiate organisms based on acetamide usage Bacitracin Susceptibility = Presumptive identification of beta-hemolytic streptococci</p> Signup and view all the answers

    What is the positive result of the biochemical test for ammonia production?

    <p>Royal blue color</p> Signup and view all the answers

    Which organism is indicated as positive in the quality control for ammonia production?

    <p>Pseudomonas aeruginosa</p> Signup and view all the answers

    What is the negative result for ammonia production?

    <p>No color change</p> Signup and view all the answers

    Biochemical tests are based on the metabolic processes that occur in microorganisms along with ______ activities that allow for rapid identification.

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

    What is the unique purpose of acetate utilization testing?

    <p>Differentiate organisms based on their ability to use acetate as the sole source of carbon.</p> Signup and view all the answers

    What is the principle behind acetamide utilization?

    <p>Production of acylamidase</p> Signup and view all the answers

    Which organism is positive for acetamide utilization according to quality control?

    <p>Escherichia coli</p> Signup and view all the answers

    What is the role of bacitracin in the bacitracin susceptibility test?

    <p>Inhibit bacterial cell wall synthesis</p> Signup and view all the answers

    A disk impregnated with bacitracin is placed on an agar plate to allow the antibiotic to ______ into the medium.

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

    What indicates a positive result in the bacitracin susceptibility test?

    <p>Zone of inhibition</p> Signup and view all the answers

    Study Notes

    Biochemical Tests in Microbiology

    • Biochemical tests are used to identify bacteria based on their metabolic processes and enzymatic activity.
    • Each test involves adding specific reagents to a sample of bacteria.
    • Different bacterial species have unique sets of biochemical reactions, allowing for their differentiation.

    Ammonia Production

    • The ammonia production test measures a bacteria's ability to produce ammonia from a specific substrate.
    • A positive ammonia production result is indicated by a change in the medium's color from green to royal blue, indicating an alkaline pH.
    • Example: Pseudomonas aeruginosa is positive for ammonia production, while Escherichia coli is negative.

    Acetate Utilization

    • This test differentiates organisms based on their ability to use acetate as a carbon source.
    • Bacteria able to utilize acetate can grow on the medium, causing a change in the medium's pH to alkaline, turning the indicator from green to blue.
    • Example: Shigella sp. is positive for acetate utilization, while Escherichia coli is negative.

    Acetamide Utilization

    • This test identifies organisms capable of using acetamide as a carbon source.
    • Bacteria capable of growth on this medium produce the enzyme acylamidase, which converts acetamide to ammonia.
    • Example: Escherichia coli is positive for acetamide utilization, while Shigella sonnei is negative.

    Bacitracin Susceptibility / TAXO A

    • This test differentiates beta-hemolytic group A streptococci (susceptible) from other beta-hemolytic streptococci (resistant).
    • It also differentiates staphylococci (resistant) from micrococci (susceptible).
    • The test uses a disk impregnated with bacitracin, which inhibits the growth of susceptible bacteria.

    Bile Esculin Hydrolysis

    • This test is used to presumptively identify and differentiate Enterococcus species.
    • Enterococci grow in the presence of 4% bile and hydrolyze esculin to esculetin, which reacts with Fe3+ to form a dark brown to black precipitate.
    • A blackening of the medium indicates a positive result, indicating Enterococcus may be present.

    Biochemical Tests

    • Biochemical tests are crucial for identifying bacteria.
    • These tests rely on the metabolic processes and enzymatic activities of microorganisms.
    • Each test helps differentiate microorganisms by their unique biochemical reactions.

    Ammonia Production

    • Ammonia production results in an alkaline pH, changing the medium from green to royal blue.
    • A blue color indicates a positive test, while no color change means a negative result.
    • Pseudomonas aeruginosa is a positive control for ammonia production.
    • Escherichia coli is a negative control for ammonia production.

    Acetate Utilization

    • This test helps distinguish organisms based on their ability to use acetate as a carbon source.
    • Organisms capable of using acetate grow on the medium, making it alkaline and turning the indicator from green to blue.
    • A blue color signifies a positive result.
    • No growth or no color change suggests a negative test.
    • This test is used to differentiate Shigella sp. from Escherichia coli.

    Acetamide Utilization

    • The acetamide utilization test differentiates organisms based on their ability to use acetamide as a carbon source.
    • Organisms capable of growth on this medium can use acetamide, producing the enzyme acylamidase.
    • Acylamidase deaminates acetamide, releasing ammonia.
    • Escherichia coli is a positive control.
    • Shigella sonnei is a negative control.

    Bacitracin Susceptibility / TAXO A

    • Used for presumptive identification and differentiation of beta-hemolytic group A streptococci from other beta-hemolytic streptococci.
    • Bacitracin inhibits the synthesis of bacterial cell walls.
    • A disc containing bacitracin is placed on an agar plate, allowing diffusion into the medium.
    • This test also differentiates staphylococci and micrococci.
    • Group A streptococci (Streptococcus pyogenes) are susceptible to Bacitracin and exhibit a zone of inhibition around the disc.

    Bile Esculin Hydrolysis

    • Used to differentiate organisms capable of growing in the presence of 4% bile and hydrolyzing esculin to esculetin.
    • Hydrolysis of esculin produces esculetin which reacts with Fe3+ and forms a dark brown to black precipitate.
    • Blackening of the agar slant suggests a positive result.

    Bile Esculin Hydrolysis: Principle

    • This test is used to differentiate bacteria based on their ability to hydrolyze esculin in the presence of bile salts.
    • Some bacteria produce the enzyme esculinase, which breaks down esculin into esculetin and glucose.
    • Esculetin reacts with iron salts in the medium, resulting in a dark brown to black precipitate.
    • Organisms capable of growing in the presence of 4% bile and hydrolyzing esculin to esculetin are considered positive.
    • This test distinguishes organisms like Enterococcus, which can tolerate bile and hydrolyze esculin, from other streptococci that are either bile-sensitive or lack the enzyme esculinase.

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    Unit Nine Biochemical Tests PDF

    Description

    This quiz covers the essential biochemical tests used in microbiology to identify bacteria based on their unique metabolic processes. Focused on tests like ammonia production and acetate utilization, it explores the significance of these reactions in distinguishing bacterial species. Perfect for microbiology students seeking to deepen their understanding of bacterial identification.

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