Microbiology lab test
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what are the 3 advantages of wet mounts
- They can be used to view living organisms.
- Motility can be viewed.
- Because they are not heat fixed; grouping of oragnisms is not disturbed.
list steps of wet mount (2)
- 1) Using pipet, place small drop of the liquid to be viewed in the center of a slide.
- 2) Place cover slip over the drop, making sure it is droped at 45 deg angle and not straight down to avoid air bubbles.
list steps of preparing a hanging drop wet-mount.
- 1) hold slip cover with the fingers of one hand.
- 2) with pipet place very small drop on slip cover.
- 3) quickly invert slip cover over the depression of a depression slide.
what are the advantages of staining microbes? (3)
- Because of increased contrast microbes are easier to see.
- Because a cover slip is not used, oil immersion can be used increasing the magnification.
- Stained slides can be saved for future observation.
What are the disadvantages of stained microbes? (2)
- Because the microbes must be heat affixed to the slide which kills the microbes motility can not be seen.
- The natural arrangment of bacteria will be disrupted as a result of the preparation of the slide.
Describe the steps in preparing a smear from a broth
- Make sure you are using a clean slide
- If microbes are settled to the bottom of the tube gently agitate the tube shaking it from side to side not up and down.
- Spread a loop full of broth about the size of a dime on the middle of the slide.
- Air dry the slide never use the burner to dry.
- Heat fix the slide by passing through the cone tip of the blue flame 3 times.
describe the steps in preparing a smear from an agar surface
- place a small drop of water on the slide.
- remove the bacteria from the slant and spread them in the water to the size of a dime.
- air dry
- heat affix
decribe the simple staining procedure.
- place a few drops of metholyne blue over the smear and wait one minute.
- holding the slide angled down over the sink slowly run water over it.
- blot the slide with bulbous paper
describe the steps involved in using the oil immersion objective.
- get the bateria focused with the high-dry objective.
- rotate objectives to in between high dry and oil immersion.
- place a drop of immersion oil directly over condenser.
- rotate immersion objective into place.
- adjust the fine adjustment to focus.
- after use discard slide into container on the counter.
- clean objective with immersion oil cleaner and lens paper a few times.
Describe the difference between a simple stain and a differential stain?
a simple stain cannot differentiate between different bacteria and a differential stain can
describe the goal of a gram stain procedure
to differentiate between different bacterias
steps of the gram stain procedure
- 1 cover the smear with crystal violet wait 1 min rinse and shake.
- 2 cover the smear with grams iodine wait 1 min rinse and shake
- 3 cover smear with denatured alcohol wait 15 secs rinse and shake
- 4 cover the smear with safranin wait 1 min rinse and shake
what are the 4 staining agents used in gram staining and thier function
- crystal violet - primary stain
- grams iodine - mordant (reinforces attachment to cell wall)
- ethonol - decolorizer
- safrinin - counter stain
what are some problems that could occur if a stain is done improperly or smear is too heavy.
it could expierience grams variabilty where a slide appears to have both gram positive and gram negative. A heavy smear will also interupt the decolorizing step causing gram neg bacteria to appear gram pos.
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