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Questions and Answers
Bile salts are stored in the intestine.
False
A lobe is the entire organ.
False
E. coli and Klebsiella spp. are lactose-non-fermenting organisms.
False
MUCOID means resembling a mineral.
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Enrichment medium is used to inhibit the growth of fastidious bacteria.
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Chocolate agar is a selective growth medium.
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A pure culture of bacteria can be obtained by spreading a large sample on the surface of a solid medium.
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Agar is a nutritional substance used in the preparation of solid media.
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Semi-solid media are used to observe the motility of bacteria.
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Nutrient agar and nutrient broth are used to grow different types of bacteria.
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The spread plate technique is used to quantify bacteria in a solid medium.
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Solid media are used to observe the motility of bacteria.
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Broth culture is a type of solid medium used to grow bacteria.
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Tryptic soy broth is a complex medium.
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MacConkey agar is an enriched medium.
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Chemically defined media are used in the identification of bacteria.
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Eosin Methylene Blue (EMB) agar is an enriched medium that supports the growth of fastidious bacteria.
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Brain heart infusion (BHI) is a selective medium.
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Haemophilus species can grow on Mueller Hinton Agar (MHA).
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EZ medium is an example of a complex medium.
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A larger zone of inhibition (ZOI) on Mueller Hinton Agar (MHA) indicates that the bacterium is resistant to the antibiotic.
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Nutrient broth is a chemically defined medium.
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Neisseria gonorrhoeae can grow on Eosin Methylene Blue (EMB) agar.
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If no zone of inhibition (ZOI) is observed on Mueller Hinton Agar (MHA), it indicates that the bacterium is sensitive to the antibiotic.
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Mueller Hinton Agar (MHA) is used for the routine susceptibility testing of fastidious microorganisms.
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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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Description
Learn about the importance of media for culturing microbes, including nutritional requirements and specialized media for different microorganisms.
