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Questions and Answers
Bile salts are stored in the intestine.
Bile salts are stored in the intestine.
False
A lobe is the entire organ.
A lobe is the entire organ.
False
E. coli and Klebsiella spp. are lactose-non-fermenting organisms.
E. coli and Klebsiella spp. are lactose-non-fermenting organisms.
False
MUCOID means resembling a mineral.
MUCOID means resembling a mineral.
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Enrichment medium is used to inhibit the growth of fastidious bacteria.
Enrichment medium is used to inhibit the growth of fastidious bacteria.
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Chocolate agar is a selective growth medium.
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.
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.
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.
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.
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.
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.
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.
Broth culture is a type of solid medium used to grow bacteria.
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Tryptic soy broth is a complex medium.
Tryptic soy broth is a complex medium.
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MacConkey agar is an enriched medium.
MacConkey agar is an enriched medium.
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Chemically defined media are used in the identification of bacteria.
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.
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.
Brain heart infusion (BHI) is a selective medium.
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Haemophilus species can grow on Mueller Hinton Agar (MHA).
Haemophilus species can grow on Mueller Hinton Agar (MHA).
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EZ medium is an example of a complex medium.
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.
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.
Nutrient broth is a chemically defined medium.
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Neisseria gonorrhoeae can grow on Eosin Methylene Blue (EMB) agar.
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.
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.
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.
