Lab Exam 1 Flashcards
Where are cells in lab grown?
closed or batch system
Nutrient solutions used to grow microbes in the laboratory
Culture medium
Where is culture medium typically sterilized?
In autoclave
Introduction of microbes into a medium
Inoculum
Microbes growing in or on a culture medium
Culture
What is a liquid culture media called? solid?
liquid: BROTH media
Solid: broth media w/ agar
What temperature does agar liquefies and solidifies?
Liquid: above 95 degrees C
Solid: 45 degrees C
T/F Agar is generally not metabolized, nor degraded by microbes
Laboratory Culture
TRUE
Exact chemical composition
of media is known
Chemically defined media
Extracts and digests yeast, meat, or plants; chemical composition varies batch to batch
Complex media:
All pure culture cells are genetically identical T/F
TRUE
What do cells grown in pure culture allow you to study?
the activities of a specific species
Pure culture obtained using _________ _________
aseptic technique
_______ acid = waxy layer on acid fast stain
mycolic
Define Resolving Power
The ability of a microscope to distinguish two close objects as separate.
How do you calculate the scale of a drawing?
Scale = Drawing size / Actual size
Q: How can you recognize a capsule stain?
A: clear halo around the stained bacterial cells.
1 mm = ___ μm
1 cm = ___ mm = ___ μm
1 μm = 10^-3 mm = ____ cm
1 m = _____ cm = 10^___ μm’
1 μm = 10 ^ __ m
1 mm = 1000 μm
1 cm = 10 mm = 10,000μm
1 μm = 10^-3 mm = 10^-4 cm
1 m = 100 cm = 10^6 μm
1 μm = 10 ^ -6 m
Q: What 2 reagents are used in a capsule stain?
A: Primary stain (Congo red) and a counterstain (Maneval’s stain).
Q: What molecules might be found in a capsule?
A: Polysaccharides or polypeptides.
Q: How do you recognize gram-positive and gram-negative bacteria?
A: Gram-positive: stains purple, retained by the thick peptidoglycan layer.
Gram-negative: stains pink, thin PTG layer
What ingredient makes nutrient broth solidify?
agar
Provide an example of a gram + and a gram - bacteria we looked at in lab
gram+ : S. epidermidis, S. aureus
gram- : Ps. fluorescens, E. coli
At what temperature and pressure are things autoclaved?
121° C, 15 psi
Why are plates incubated upside down?
To prevent condensation from dripping onto the agar.
Q: What dyes are used in a Gram stain and their purposes?
- Crystal violet: Primary stain.
- Iodine: Mordant.
- Alcohol: Decolorizer.
- Safranin: Counterstain.
What is a negative stain used for?
To visualize cells without heat-fixing; used for delicate cells like spirochetes.
What dye is used in a negative stain, and is it neutral, basic, or acidic?
Nigrosin, an acidic stain.
Name three basic dyes.
- Crystal violet
- methylene blue
- safranin
Q: What are the differences between the cell walls of gram-positive and gram-negative bacteria?
A: Gram-positive: Thick peptidoglycan layer.
Gram-negative: Thin peptidoglycan layer and outer membrane.
Name an acidic dye
- Eosin
- Nigrosin
- India Ink
- Congo Red
- Acid Fuchsin
Q: How do you recognize a spore/Schaeffer-Fulton spore stain under a microscope?
A: Spores appear as green in a spore stain, with the vegetative cells appearing pink/red.
Q: What reagents are used in a Schaeffer-Fulton spore stain?
A: Malachite green (stains spores) and safranin (counterstains cells).
Q: Why do bacteria form spores?
A: To survive harsh conditions (e.g., heat, lack of nutrients).
What is a simple stain?
uses a single dye to visualize cells.
Why are slides heat fixed before staining? (2 reasons)
- kill bacteria
- adhere bacteria to slide
What shape is cocci? bacillus?
cocci: spherical
bacilli: rod-shaped
Q: Name a genus of a spore-forming bacterium.
A: Bacillus or Clostridium.
Q: What cell wall component makes an acid-fast bacterium acid-fast?
A: Mycolic acid.
Q: What reagents are used in an acid-fast stain?
- Basic fuchsin (stains red)
- acid alcohol (decolorizer)
- methylene blue (counterstain).
What color do acid-fast bacterium stain?
Acid-fast bacterium stain red
Q: What is the purpose of the acid-fast stain?
A: To identify bacteria with waxy, resistant cell walls (e.g., Mycobacterium).
Q: Name an acid-fast and non-acid-fast bacterium.
A: Acid fast: Mycobacterium tuberculosis, M. smegmatis (stains red, positive, pathogenic)
Non-acid-fast: S. aureus (stains blue, negative)
Q: How do you do a bacterial dilution problem?
A: Use serial dilutions to calculate the concentration of bacteria based on colonies counted. Follow the formula:
CFU/mL = (Number of colonies × dilution factor) / volume plated.
total mag μm/div
_____ 25 μm/div
100x ________
_______ 2.5 μm/div
1000x ________
total mag μm/div
40x 25 μm/div
100x 10 μm/div
400x 2.5 μm/div
1000x 1.0 μm/div
