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What is the primary outcome of biological selection in a population?
Natural selection is defined as humans choosing which organisms survive.
False
What is an example of selective media used to isolate Neisseria gonorrhoeae?
Thayer-Martin agar
A medium that allows for the growth of specific organisms while inhibiting others is known as __________ media.
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Match the following types of media with their functions:
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Which of the following is NOT considered an agent of artificial selection?
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Blood agar is an example of selective media.
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Name an example of differential media.
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The ability of bacteria to ferment lactose is indicated by a change in color on ________ agar.
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What happens to bacteria on differential media when they produce hemolysin on Blood agar?
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What is the primary purpose of sterilization?
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The viable counting method only measures dead microorganisms.
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Name two methods used for viable counting of microbial populations.
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___ is the removal of pathogens from living tissue.
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Which temperature and duration combination is NOT typical for pasteurization of milk?
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Match the following terms with their definitions:
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Commercial sterilization targets the elimination of Clostridium botulinum endospores.
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The process used to lower microbial counts on eating utensils is called ___ .
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What is a common physical method of controlling microbial growth?
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What is the main goal when applying pasteurization to food products?
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Study Notes
Biological Selection
- Populations experience differential survival due to limiting environments.
- Artificial selection is driven by human choices for desirable traits.
- Natural selection occurs as the environment determines survival.
- Changes in allele frequency reflect genetic makeup shifts within a population.
Examples of Artificial Selection Agents
- Includes herbicides, pesticides, antibiotics, anti-tumor drugs, and anti-virals.
- Environmental factors like salt, temperature, and oxygen also influence selection.
- Traits selected for can include size, taste, or yield.
Laboratory Cultivation
- Selective media inhibit unwanted organism growth and allow target microbes to thrive.
- Requires prior knowledge for effective use.
- Examples include:
- Thayer-Martin agar: isolates Neisseria gonorrhoeae.
- MacConkey agar: selective for Gram-negative bacteria.
- Mannitol Salt Agar: isolates osmotolerant organisms.
Differential Media
- Contains substances that bacteria alter visibly.
- Example:
- Blood agar: detects hemolysin production that breaks down red blood cells (hemolysis).
- In MacConkey agar, a pH indicator differentiates bacteria that produce acid.
Growth Detection Methods
- Indicators of bacterial growth include turbidity, metabolite production, and culture-independent methods.
- Microscopic Counts: Involves directly observing cells in liquid samples or on slides using counting chambers for precision.
Viable Counting
- Viable counts measure living microbial populations using two main techniques:
- Spread-plate method
- Pour-plate method
- Count colonies between 30-300 for accuracy.
- Dilution before counting is essential for proper colony number.
Control of Bacterial Growth
- Goal may include ceasing growth, reducing levels below infectious doses, and adhering to regulations through sterilization.
- Control methods utilize physical or chemical means or a combination of both.
Approaches to Control
- Physical methods: Include heat, irradiation, filtration, and mechanical removal.
- Chemical methods: Vary based on circumstances and the required control strength.
Microbial Control Principles
- Sterilization: Complete removal of all microorganisms, including endospores and viruses. Achievable through various methods like filtration and heat.
- Disinfection: Eliminates most pathogens, with some viable microbes possibly remaining. Disinfectants are for inanimate objects, antiseptics for living tissues.
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Pasteurization: Heat treatment aimed at reducing spoilage organisms. Examples include:
- 63°C for 30 min (Vat Pasteurization)
- 72°C for 15s (HTST)
- 96°C for 0.05s (HHST)
- 138°C for 2s (Ultra Pasteurization)
Terminology
- Sterilization: Complete removal of microbial life.
- Commercial sterilization: Targets Clostridium botulinum endospores.
- Disinfection: Pathogen removal from surfaces and items.
- Antisepsis: Pathogen removal from living tissues.
- Degerming: Localized removal of microbes.
- Sanitization: Reduces microbial counts on utensils.
- Biocide/Germicide: Kills microbes; Bacteriostatic: inhibits growth without killing.
Bacterial Death Rate
- Bacterial populations decrease at a consistent logarithmic rate, aiding in understanding growth control.
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Description
This quiz covers the concepts of natural and artificial selection, including their mechanisms and examples. It also explores selective media used in laboratory cultivation for isolating and identifying specific microbes. Test your understanding of differential survival and microbial selection techniques.
