Unit 7: Culturing bacteria
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Unit 7: Culturing bacteria

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Questions and Answers

Which of the following genera includes some common human pathogenic species of Enterobacteriaceae?

  • Bacillus
  • Streptococcus
  • Neisseria
  • Citrobacter (correct)

    • Salmonella enterica is a genus of the Enterobacteriaceae family known for causing intestinal diseases.

    True

    Name one differential media used for detecting fecal coliform bacteria.

    Eosin Methylene Blue Agar

    The enteric bacterium _____ is responsible for causing plague.

    <p>Yersinia pestis</p> Signup and view all the answers

    Match the following Enterobacteriaceae species with their characteristics:

    <p>Escherichia coli = Pathogen associated with foodborne illness Klebsiella pneumoniae = Known for causing pneumonia and UTIs Shigella flexneri = Causes bacillary dysentery Proteus mirabilis = Associated with urinary tract infections</p> Signup and view all the answers

    What is the primary purpose of culturing bacteria?

    <p>To play detective and identify microorganisms</p> Signup and view all the answers

    The pour plate method is primarily used for separating mixed cultures.

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

    What is a pure culture?

    <p>A culture that contains cells from a single species of an organism.</p> Signup and view all the answers

    The _______ method is effective for isolating pure colonies from mixed cultures.

    <p>streak plate</p> Signup and view all the answers

    Match the culturing methods with their primary uses:

    <p>Streak Plate Method = Isolating pure colonies Pour Plate Method = Counting bacteria Serial Dilution = Preparing sample dilutions Culture Media = Providing nutrients for growth</p> Signup and view all the answers

    Which of the following is NOT a type of culture medium?

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

    All bacteria can grow on the same type of culture medium.

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

    What is one condition that bacteria may require for growth?

    <p>Anaerobic conditions</p> Signup and view all the answers

    What type of bacteria does Mannitol Salt Agar primarily isolate?

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

    Lactose fermenters on MacConkey agar produce red colonies.

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

    What is the primary purpose of Hektoen Enteric Agar?

    <p>To select and differentiate Salmonella and Shigella species</p> Signup and view all the answers

    The ______ agar is used to differentiate blood hemolysis types.

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

    Match the type of agar with its characteristic:

    <p>MacConkey Agar = Selection for Gram-negative bacteria Mannitol Salt Agar = Isolation of Staphylococci Bismuth Sulfite Agar = Isolation of S. typhi Blood Agar = Differentiation of hemolytic bacteria</p> Signup and view all the answers

    What color do Salmonella colonies appear on Hektoen Enteric Agar?

    <p>Transparent green with black centers</p> Signup and view all the answers

    Beta hemolytic bacteria cause incomplete breakdown of red blood cells.

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

    What is the function of bile salts in selective media?

    <p>To inhibit the growth of Gram-positive bacteria</p> Signup and view all the answers

    What does a yellow broth indicate in carbohydrate fermentation tests?

    <p>Acid production has occurred</p> Signup and view all the answers

    The oxidase reaction tests for the presence of lecithinase.

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

    What enzyme is tested for in the egg-yolk reaction?

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

    The enzyme that allows bacteria to reduce nitrate is called __________.

    <p>nitrate reductase</p> Signup and view all the answers

    Match the biochemical test with its purpose:

    <p>Nitrate reduction = Determines enzyme presence for nitrate reduction Oxidase reaction = Tests for cytochrome-oxidase presence Indole production = Tests for breakdown of tryptophan Egg-yolk reaction = Tests for lecithinase enzyme</p> Signup and view all the answers

    In the indole production test, what color indicates a positive result?

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

    A Durham tube is not necessary in carbohydrate fermentation tests.

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

    Which type of media is Eosin Methylene Blue Agar classified as?

    <p>Differential Media</p> Signup and view all the answers

    What is the role of phenol red in carbohydrate fermentation tests?

    <p>pH indicator</p> Signup and view all the answers

    The Pour Plate Method is primarily used for isolating single colonies from solid media.

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

    What is the purpose of the Phenol red broth with Durham tube in biochemical tests?

    <p>To detect fermentation of particular carbohydrates.</p> Signup and view all the answers

    Tryptophan breakdown can be assessed using _____ and Kovacs reagent.

    <p>tryptophan broth</p> Signup and view all the answers

    Which test indicates the ability of bacteria to produce and maintain acid products from glucose fermentation?

    <p>Methyl Red test</p> Signup and view all the answers

    Match the following biochemical tests with their corresponding media:

    <p>Litmus Test = Litmus milk medium Urease test = Urea media Indole Production = Tryptophan broth Methyl Red test = Methyl red solution</p> Signup and view all the answers

    Blood Agar is classified as selective media.

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

    The _____ test determines if ammonia is produced when media containing urea is used.

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

    Study Notes

    Culturing Bacteria

    • A culture is a group of microorganisms that grow in a medium.
    • A medium is a solid, liquid, or semi-solid that supports the growth of microorganisms.
    • Common media include broth, agar, and enriched media.
    • Microbiologists can identify microorganisms by studying their characteristics and culturing them in appropriate media.

    Culturing Bacteria

    • Pure cultures contain cells from a single species of an organism.
    • The chosen medium must meet the organism's enzyme and nutritional requirements.
    • Streak plating is used to isolate pure samples.
    • Pour plating is used to count bacteria and obtain pure cultures.
    • Serial dilution is a technique involved in the pour plate method.
    • Serial dilution helps isolate single colonies for further study.

    Estimating Bacterial Numbers

    • Choose a plate with between 30 and 300 colonies for accurate counting.
    • Multiply the number of colonies by the reciprocal of the dilution factor to estimate total bacteria.
    • Express the result in scientific notation.

    Culture Media

    • Culture media contains all nutrients needed for bacterial growth.
    • Microbiologists must understand the nutritional needs of bacteria to provide them with the necessary nutrients in an artificial environment.
    • No single media supports the growth of all bacteria.
    • Anaerobic conditions may be needed for certain species.

    Common Human Pathogenic Enterobacteriaceae

    • This table lists several common human pathogenic Enterobacteriaceae species and their associated genus.

    Differential Media

    • Differential media allow for the differentiation of bacteria based on their characteristics.
    • Eosin Methylene Blue (EMB) Agar:
      • Detects fecal coliform bacteria.
      • Contains Eosin Y and Methylene blue as pH indicators.
      • Inhibits Gram-positive bacteria.
      • Fermentable carbohydrates include lactose and sucrose.
      • Rapid fermenters produce green metallic colonies.
      • Medium fermenters produce pink colonies.
      • Non-coliforms produce colorless colonies.
    • MacConkey Agar:
      • Selective and differential.
      • Selects for Gram-negative bacteria.
      • Contains lactose, crystal violet, bile salts, and neutral red indicator.
      • Lactose fermenters produce red colonies.
      • Non-lactose fermenters produce colorless colonies.
    • Hektoen Enteric Agar:
      • Selective and differential.
      • Selects and differentiates Salmonella and Shigella from other Enterobacteriaceae.
      • Contains bile salts and bromothymol blue, inhibiting Gram-positive bacteria.
      • Ferrous compounds are present to indicate hydrogen sulfide gas production.
      • Salmonella colonies produce transparent green colonies with black centers.
      • Shigella colonies produce transparent green colonies.
      • Lactose fermenters produce salmon-colored colonies.
    • Mannitol Salt Agar:
      • Selective and differential.
      • Isolates Staphylococci (Gram-positive bacteria).
      • Contains a high salt concentration (7.5%), inhibiting halophobic growth.
      • Pathogenic Staphylococci ferment mannitol, producing yellow colonies.
      • Non-pathogenic Staphylococci do not ferment mannitol, producing pink colonies.

    Selective Media

    • Bismuth Sulfite Agar:
      • Isolates Salmonella typhi (typhoid fever).
      • Contains bismuth sulfite and Brilliant green indicators, inhibiting Gram-positive and coliform bacteria.
      • The presence of S. typhi reduces sulfide, resulting in black or green metallic colonies.

    Enrichment Media

    • Tryptic Soy Agar and Broth (TSA/B):
      • General purpose non-selective media.
      • Provides ample nutrients for a wide range of bacterial species.
      • Frequently used in general microbiology labs.
    • Blood Agar:
      • Contains general nutrients and 5% bovine (cow or sheep) blood.
      • Differentiates between hemolytic and non-hemolytic bacteria.
        • Alpha hemolytic bacteria: partially break down RBCs and produce a green color (e.g., Streptococcus pneumoniae).
        • Beta hemolytic bacteria: completely break down RBCs and cause clearing (e.g., Staphylococcus sp. and Streptococcus sp.).
        • Gamma hemolytic bacteria: can grow but do not break down RBCs (e.g., Staphylococcus sp.).
    • Chocolate Agar:
      • Blood is added to tryptic soy agar and heated, causing the blood to lyse and release the nutrients.

    Biochemical Tests

    • Carbohydrate Fermentation Tests:
      • Use phenol red broth with a Durham tube.
      • Detects the fermentation of specific carbohydrates.
      • Positive result: broth turns yellow (acidic).
      • Negative result: broth stays red/pink (neutral).
      • Gas production is indicated by bubbles in the Durham tube.
    • Litmus Test:
      • Uses litmus milk medium with litmus indicator.
      • Evaluates a bacteria's ability to use different milk products.
      • Color changes, gas production, or curdling of the media indicate positive results.
    • Indole Production:
      • Uses tryptophan broth and Kovacs reagent.
      • Detects the ability of bacteria to break down tryptophan into indole.
      • Positive result: pink color forms on the surface of the broth.
    • Methyl Red Test:
      • Uses Methyl Red-Voges-Proskauer (MRVP) media and Methyl Red solution.
      • Detects the ability of bacteria to produce and maintain acidic products from glucose fermentation.
      • Positive result: red color remains after adding the Methyl Red solution.
    • Urease Test:
      • Uses media containing urea.
      • Detects the enzyme urease.
      • Positive result: ammonia production turns the litmus indicator basic (color change).
    • Nitrate Reduction:
      • Uses media containing nitrate.
      • Detects the enzyme nitrate reductase.
      • Positive result: the production of nitrites is observed.
    • Oxidase Reaction:
      • Uses TSA/B and oxidase reagent.
      • Detects the presence of cytochrome-oxidase, a key enzyme in the electron transport chain (ETC).
      • Positive result: a blue color appears.
      • This test helps determine a bacteria's ability to produce energy aerobically using the ETC.
    • Egg-Yolk Reaction:
      • Uses egg-yolk agar.
      • Detects the enzyme lecithinase, which destroys animal tissue.
      • Positive result: a white precipitate forms around the colonies (indicates lecithinase activity).

    Recall - Pour Plate Method

    • A serial dilution is performed from a liquid specimen.
    • Each dilution is used to pour a plate inoculated with bacteria in agar.
    • Colonies are counted after incubation.
    • A plate with single, pure colonies is selected for further growth.

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    BIOL2010 Week 7 Culturing Bacteria PDF

    Description

    This quiz covers the fundamentals of culturing bacteria, including the types of media used and methods of isolating pure cultures. You'll explore techniques such as streak plating and pour plating, along with estimating bacterial numbers through colony counts. Test your understanding of these essential microbiological practices.

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