Lab 1 Flashcards
(33 cards)
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
Describe the naming of bacteria.
Uses the binary system of genus + species
* Genus – 1st letter capitalized
* Species – all lower case
* Also italicized (or underlined if hand-written).
e.g., Staphylococcus epidermidis, Escherichia coli
Once the full name has been used in a text, the genus name can be written with a single letter.
e.g., S. epidermidis, E. coli
What is ‘cleaning’?
- physically remove the different contaminants from the surface using water/detergent
- doesn’t necessarily kill microbes
- reduces microbial count from surfaces
What is sanitizing?
- refers to lowering the number of microbes on a surface to a “safe level”
- many sanitizing agents only reduce the specific bacteria listed on the products label
- mostly effective against bacteria, less effective against viruses
What is disinfecting?
- actually killing the microbes on the surface through the use of a chemical agent
- destroys and inactivates both bacteria and viruses
- works best on hard, non-porous surfaces
What is sterilization?
- killing and inactivating harmful microorganisms and viruses
- disinfecting only kills some of microorganisms, the process of sterilization kills all microorganisms
- typically not practical for the home or for the workplace
How is culture media prepared?
How are saline dilution blanks prepared?
How do we sterilize media?
Autoclave
* used to sterilize equipment and supplies by subjecting them to pressurized saturated steam at 121oC at a pressure of 15 pounds per square inch (psi) (or 103 kPa)
* held for around 30-60 minutes depending on the size of the load and the contents.
What 3 things are important lab technique in microbiology?
1. Sterilization
* using an autoclave (high temperature, steam, pressure) - media, pipette tips.
* heat i.e., flaming equipment using an Bunsen burner - loop inoculators.
* dry heat i.e., glass pipettes, glassware.
2. Disinfecting
* using a quaternary ammonium compound to clean lab surfaces.
* using 70% alcohol.
3. Cleaning
* washing glassware after autoclaving.
* washing hands, washing lab coat.
