Microbiology Culture Media
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Questions and Answers

What is the characteristic coloration of the medium resulting from red blood cell lysis?

  • Yellow
  • Chocolate-brown (correct)
  • Purple
  • Red

    • Which bacterial pathogens require enriched medium for growth?

  • Neisseria gonorrhoeae and Haemophilus species (correct)
  • Pseudomonas aeruginosa and Klebsiella pneumoniae
  • E. coli and Salmonella
  • Staphylococcus aureus and Bacillus subtilis

    • What is the purpose of Eosin Methylene Blue (EMB) agar?

  • To selectively grow Gram-positive bacteria
  • To differentiate between lactose fermenters and non-fermenters (correct)
  • To inhibit the growth of Gram-negative bacteria
  • To identify Haemophilus species

    • What type of colonies are typically produced by lactose-fermenting E. coli on EMB agar?

    <p>Flat, dark colonies with a green metallic sheen</p> Signup and view all the answers

    What is the purpose of Mueller Hinton Agar (MHA)?

    <p>To perform routine susceptibility testing by the Kirby-Bauer disk diffusion technique</p> Signup and view all the answers

    What does a smaller zone of inhibition (ZOI) indicate in the Kirby-Bauer disk diffusion technique?

    <p>Lower sensitivity to the antibiotic</p> Signup and view all the answers

    What does the absence of a zone of inhibition (ZOI) indicate in the Kirby-Bauer disk diffusion technique?

    <p>The organism is resistant to the antibiotic</p> Signup and view all the answers

    What is the name of the technique used with Mueller Hinton Agar (MHA) for susceptibility testing?

    <p>Kirby-Bauer disk diffusion technique</p> Signup and view all the answers

    What type of medium is Eosin Methylene Blue (EMB) agar?

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

    What is the purpose of red blood cell lysis in the preparation of the medium?

    <p>To give the medium a characteristic color</p> Signup and view all the answers

    What is the primary location of Enterobacteriaceae species?

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

    What is the term for a part of an organ that appears to be separate in some way?

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

    Which of the following organisms ferment lactose?

    <p>E.coli</p> Signup and view all the answers

    What is the purpose of enrichment medium in microbiology?

    <p>To support the growth of fastidious bacteria</p> Signup and view all the answers

    What is the composition of blood agar?

    <p>Autoclaved basal media with 5% defibrinated mammalian blood</p> Signup and view all the answers

    What is the purpose of heating the blood to 80°C in chocolate agar?

    <p>To lyse red blood cells</p> Signup and view all the answers

    What is the term for resembling mucus?

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

    What is the purpose of MacConkey agar?

    <p>To differentiate between lactose-fermenting and lactose-non-fermenting bacteria</p> Signup and view all the answers

    Which of the following bacteria is a lactose-non-fermenting organism?

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

    What is the function of NAD in chocolate agar?

    <p>To provide nutrients to fastidious bacteria</p> Signup and view all the answers

    What is a pure culture?

    <p>A laboratory culture containing a single species of organism.</p> Signup and view all the answers

    What is the purpose of using a solidification agent in solid and semi solid media?

    <p>To solidify the media.</p> Signup and view all the answers

    What is the main difference between nutrient agar (NA) and nutrient broth (NB) culture?

    <p>NA contains a solidifying agent, while NB does not.</p> Signup and view all the answers

    What is the purpose of the spread plate technique?

    <p>To isolate and enumerate microorganisms in a mixed culture.</p> Signup and view all the answers

    What is the result of a single cell occupying an isolated portion of the agar surface?

    <p>A visible colony of similar cells.</p> Signup and view all the answers

    What is the characteristic of semi solid media?

    <p>It contains a low amount of agar.</p> Signup and view all the answers

    Why is agar used in solid and semi solid media?

    <p>Because it is a solidifying agent.</p> Signup and view all the answers

    What is the main advantage of using solid media?

    <p>It is easier to isolate microorganisms.</p> Signup and view all the answers

    What is broth culture?

    <p>Any type of liquid used to grow bacteria.</p> Signup and view all the answers

    What is the result of spreading bacteria on the surface of a solid medium?

    <p>A visible colony of similar cells.</p> Signup and view all the answers

    What is the primary objective of cultivating microorganisms?

    <p>To maintain viable populations under controlled laboratory environments</p> Signup and view all the answers

    What type of medium is tryptic soy broth (TSB)?

    <p>All-purpose medium</p> Signup and view all the answers

    What is the characteristic of enriched media?

    <p>Contains growth factors, vitamins, and other essential nutrients</p> Signup and view all the answers

    What type of medium is brain heart infusion (BHI)?

    <p>Complex medium</p> Signup and view all the answers

    What is the purpose of selective media?

    <p>To inhibit the growth of unwanted microorganisms</p> Signup and view all the answers

    What is the characteristic of MacConkey agar?

    <p>Contains bile salts and crystal violet</p> Signup and view all the answers

    What is the use of BHI broth in laboratory settings?

    <p>Food safety tests and antibiotic sensitivity tests</p> Signup and view all the answers

    What is the characteristic of complex media?

    <p>Precise chemical composition is unknown</p> Signup and view all the answers

    What is the difference between chemically defined and complex media?

    <p>Chemically defined media have a complete chemical composition, while complex media do not</p> Signup and view all the answers

    What is the purpose of culturing microorganisms?

    <p>To maintain viable populations under controlled laboratory environments</p> Signup and view all the answers

    Study Notes

    Importance of Media for Culturing Microbes

    • The primary objective of cultivating microorganisms is to maintain viable populations of these organisms under controlled laboratory environments.
    • Cultivating microorganisms is a challenging process due to their highly specific nutritional and environmental requirements and the diversity of these requirements among different species.

    Nutritional Requirements of Microbes

    • All-purpose medium: Tryptic Soy Broth (TSB)
    • Specialized media: used in the identification of bacteria and are supplemented with dyes, pH indicators, or antibiotics
    • Enriched media: contains growth factors, vitamins, and other essential nutrients to promote the growth of fastidious organisms
    • Chemically defined medium: complete chemical composition of a medium is known (e.g. EZ medium)
    • Complex media: contain extracts and digests of yeasts, meat, or plants, and the precise chemical composition is not known (e.g. nutrient broth, TSB, Brain Heart Infusion (BHI))

    Types of Media

    • Selective medium: inhibits the growth of unwanted microorganisms and supports the growth of the organism of interest (e.g. MacConkey agar)
    • Enrichment medium: general purpose enrichment agar that can nourish and support the growth of gram-positive as well as gram-negative bacteria (e.g. blood agar)
    • Differential medium: distinguishes between different microorganisms based on their metabolic characteristics (e.g. Eosin Methylene Blue (EMB) agar)

    MacConkey Agar

    • Contains bile salts and crystal violet, which interfere with the growth of many gram-positive bacteria and favor the growth of gram-negative bacteria, particularly the Enterobacteriaceae
    • Lactose-fermenting organisms (e.g. E. coli) grow as pink to red colonies with or without a zone of precipitated bile
    • Lactose-non-fermenting organisms (e.g. Salmonella, Shigella) form colorless or clear colonies

    Blood Agar

    • Enriched medium that supports the growth of fastidious bacteria and inhibits the growth of some bacteria like Neisseria and Haemophilus
    • Contains 5% defibrinated mammalian blood (e.g. horse, sheep, human) added to the autoclaved basal media (TSA or Columbia Agar)

    Chocolate Agar

    • Enriched growth medium used for the isolation of pathogenic bacteria
    • Nonselective, enriched growth medium that supports the growth of fastidious bacteria
    • Contains red blood cells that have been lysed by slowly heating to 80°C, releasing intracellular nutrients

    Obtaining Pure Culture

    • A pure culture is a laboratory culture containing a single species of organism
    • Obtained by transferring a small sample into new, sterile growth medium in such a manner as to disperse the individual cells across the medium surface or by thinning the sample many fold before inoculating the new medium
    • Can be accomplished by spreading bacteria on the surface of a solid medium so that a single cell occupies an isolated portion of the agar surface

    Solid vs. Semi-Solid vs. Liquid Media

    • Solid media: contains a solidification agent (e.g. agar) and is used for the growth of microorganisms
    • Semi-solid media (deep culture): prepared with a lower concentration of agar (0.2 to 0.5%) to observe motility of bacteria
    • Liquid media (broth culture): a liquid used to grow bacteria, does not contain a solidification agent

    Spread Plate Technique

    • A method of isolation and enumeration of microorganisms in a mixed culture
    • Distributes microorganisms evenly and makes it easier to quantify bacteria in a solution

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    Lecture 6 Principles & Functions of Culture Media PDF

    Description

    This quiz covers the importance of media for culturing microorganisms, methods of obtaining pure cultures, and types of media used for bacterial growth.

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