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Questions and Answers
The enrichment culture technique is used to isolate microorganisms with all possible combinations of nutrient requirements that do not exist in nature.
False
Selective methods can be based on the tolerance of an organism to acid or alkali, heat, or radiation.
True
Cycloheximide is used to suppress the growth of bacteria.
False
The enrichment culture technique involves subculturing in different media with varying nutrient compositions.
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Tellurite-containing media is used to identify Enterobacteriaceae.
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Bismuth agar is used to identify Corynebacterium diphtheriae.
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Only β-haemolytic bacteria can grow on blood agar medium.
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Microorganisms that can be recognized by their colonial characteristics can be directly isolated.
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Enrichment culture is used to isolate microorganisms that cannot compete with other organisms in the inoculum.
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Temperature is not a factor that can be used to impose environment conditions in enrichment culture.
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Differential media are used to isolate microorganisms from a mixed culture.
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Non-haemolytic bacteria cannot grow on blood agar medium.
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Selective culture methods are used to isolate microorganisms that are present in large numbers in a sample.
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The choice of carbon source is not important in enrichment culture.
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Crystal violet is a selective agent that inhibits the growth of Gram-ve bacteria.
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The inclusion of bile salts in culture media can select the growth of Escherichia.
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The addition of 5 g/1 NaCl to culture media is used to inhibit the growth of Staphylococcus.
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Differential media are used to reveal differences between MOs or groups of MOs.
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Brief exposure to high temperature (80°C) can be used to selectively isolate spore-forming bacteria.
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Penicillin is a selective agent that inhibits the growth of Gram+ve bacteria.
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Enterobacter strains are adapted to grow at higher temperatures than Escherichia strains.
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Sodium azide is a selective agent that inhibits the growth of all bacteria.
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Study Notes
Blood Agar Medium
- Differentiates between three groups of bacteria:
- Non-haemolytic bacteria (no haemolysis)
- α-haemolytic bacteria (partial haemolysis, dark green zone)
- β-haemolytic bacteria (complete haemolysis, clear zone)
Selective Culture Methods
- Direct isolation: recognizes microorganisms by colonial characteristics, accumulation of substances, or changes in their environment
- Enrichment culture: enables microorganisms to compete and outgrow others by providing suitable growth conditions
- Repeated subculturing and plating out on solid medium allows for isolation of enriched strain or species
Enrichment Culture
- Provides specific growth conditions to enable desired microorganisms to outgrow others
- Factors influencing growth conditions include:
- Carbon, energy, and nitrogen sources
- Gaseous atmosphere
- Hydrogen acceptors
- Temperature
- Light
- pH
Selective Media
- Contain ingredients that inhibit the reproduction of unwanted microorganisms
- Selective agents include:
- Dyes (e.g., crystal violet or malachite green)
- Antibiotics (e.g., penicillin or streptomycin)
- Chemicals (e.g., sodium azide)
- Examples of selective media:
- Nutrient agar with 7.5% NaCl for isolating Staphylococcus from human skin
- Crystal violet to allow growth of Gram-ve bacteria and prevent Gram+ve
- Inclusion of bile salts to select for Escherichia strains
- Pretreatment with high temperature to eliminate non-sporulating bacteria in isolation of spore-forming bacteria
Differential Media
- Designed to reveal differences between microorganisms or groups of microorganisms
- Contain chemicals utilized or altered by some microorganisms but not others
- Examples of differential media include blood agar, which differentiates between haemolytic and non-haemolytic bacteria
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Description
This quiz covers the different types of bacterial growth on blood agar medium, including non-haemolytic, α-haemolytic, and β-haemolytic bacteria. Learn how to differentiate between these groups of bacteria based on their hemolytic activity.
