Lab 1 Flashcards
What is the streak plate technique?
- Common method of isolating unicellular organisms from a mixed culture
- Small volume distributed over agar.
- Culture media generally contain a source of carbohydrates, minerals, amino acids, and vitamins.
- The exact composition of the medium is dependent on the specific requirements of the organism you wish to isolate, or the characteristics you wish to study.
- Oxygen, pH, temperature, pressure, and incubation time are also important growth parameters.
Regardless of composition, culture media is provided in three forms: liquid, solid, and semi-solid
Describe use of liquid broth.
- To grow large numbers of bacteria (pure or mixed cultures) in a short period of time.
- Large numbers (>10^6 per/mL) of organisms cause turbidity or cloudiness in the broth.
Describe solid media.
- Contains agar
- May be:
- Plate
- Slant
What is agar and why is it used?
- A polysaccharide extracted from seaweed; solid media
- Not broken down by bacteria
- Contains no relevant nutrients required by bacteria
- Melts at high temperatures, and is solid at temperatures that facilitate bacterial growth
Describe plate media and its use.
- Solid medium in petri dish
- Generally used to purify or verify the purity of a culture
- Only form of growth in medium on which one can observe macroscopic (colony) morphology and/or isolate pure colonies from a mixed sample
Which type of media allows macroscopic morphology to be observed and/or isolation of pure colonies from a mixed sample?
Plate solid media
Describe slant media and its use.
- Solidified in a test tube in a manner that will produce a large surface area.
- Used to store cultures as they are more resistant to dehydration than agar plates.
Describe semi-solid media and its use.
- Has a low agar concentration
- Normally placed in a tube
- Used for motility studies
What is aseptic technique?
- Prevents contamination of cultures
- Allows maintenance of pure culture regardless of the number of subcultures
- Also controls how and where macroscopic cells are moved and will prevent contamination of self and working environment.
What are macroscopic morphologies?
- Characteristics often necessary for identification or characterization of microbes.
- Colony features
Describe the relevance of Pseudomonas.
- Can grow in refrigerated foods due to competitive growth rate in aerobic environments with ideal pH conditions.
- Considered aerobic spoilage organisms.
- High population densities of Pseudomonas can compete with other aerobic spoilage organisms by their ability to sequester oxygen and iron.
- Siderophores are compounds produced and secreted by Pseudomonas bacteria.
- Siderophores bind iron in the environment.
- Pseudomonas binds the sidorephores and transport the iron into the cell
- These compounds are fluorescent and can be seen under UV light.
What does bacterial dominance of specific types of aerobic spoilage depend on?
- Ability to utilize nutrients in muscle tissue, which are complex energy sources (vs. simple sugar)
How is the total magnifying power of a microscope calculated?
Why do immersion oil lenses increase resolution?
Compare bacterial cells to eukaryotes (e.g., yeast).
Bacteria:
* Much smaller
* Lack a membrane bound nucleus
* Lack mitochondria
* DNA is circular and smaller in size
* May contain plasmids
How is culture media prepared?
How are saline dilution blanks prepared?
What is binary fission?
Bacterial growth is an increase in the biomass.
The cell duplicates all its components:
* membrane,
* chromosome,
* ribosomes,
* plasmids (if present).
When the cell divides, the two daughter cells are the same size
and composition as the parental cell.
How can you generate a pure culture from a mixed culture?
Streak plating! There is more than 1 way to streak a plate.
The method use depends on personal preference.
