Microscopy
What is the first step in kohlering after you have your calibration slide on the stage?
Put something on focus using the 10X objective.
What is the purpose of the first stop on a micropipette when drawing up a liquid?
The purpose of the first stop on a micropipette is to aspirate or draw up the specific, accurate volume of liquid.
What shape and arrangement does a Staphylococcus species have?
Coccus, forming clusters.
How many milliliters are in one liter?
1000
What is the main goal of the streak plate method?
Isolate different species to create a pure culture
What do you adjust to make the field diaphragm appear as a small, sharp polygon?
The condenser height.
Why should a micropipette never be turned on its side or upside down when there is liquid in the tip?
Because the liquid could leak into the shaft, contaminating the internal mechanism and affecting future measurements.
What is the role of iodine in the Gram stain process?
Act as a mordent to prevent the crystal violet from leaving the cells during the decolorizing step.
If you have a stock solution that is 100×, how much stock do you need to make 10 mL of a 1× solution?
100 microliters.
True or False: You should sterilize/change inoculating loop after streaking each quadrant.
TRUE
What is the total magnification if you are using a 40× objective lens and a 10× ocular lens?
400x
In this experiment, why is it critical to thoroughly mix the solution after each dilution step?
To ensure the solution is homogeneous and that the calculated concentration is accurate before moving to the next dilution step.
For how long each dye must be incubated?
1 minute
What is the final concentration of a solution if you dilute 1 mL of a 5 M stock into 9 mL of diluent?
0.5M
What is the name for a visible mass of microorganisms growing on an agar plate that originated from a single cell?
Colony.
What is the purpose of immersion oil when using the 100× objective lens?
To avoid light diffraction and increase resolution.
Which labels should the y and x axis have in this experiment?
Absorbance and dilution factor.
Your original culture contains E. coli sample. What would be their gram staining results?
Bacillus gram negative.
Calculate the number of colony-forming units per milliliter (CFU/mL) if you plate 0.1 mL of a 10−6 dilution and count 50 colonies.
50 x 10^6 x 10 = 5x10^8 CFU/mL
What should I do if after incubating my culture media where I did the streaking for isolation I see different colonies colors on my media?
Continue isolating the species by doing another streaking for isolation making sure that I will only harvest cells from one single colony.
How do you center the field diaphragm in the field of view?
Using the 2 knobs located on the condenser (facing forward).
Why the spectrophotometer shows a OVRFLW message?
Because the concentration of the solution was too high to let the light pass through the solution, so the machine can't accurately meassure the optical density.
Why do Gram-negative bacteria lose the crystal violet-iodine complex during the decolorization step?
The ethanol will break their cell wall, allowing the dye to be removed from the cells.
If you need to make 250 mL of a 0.5 M solution of NaCl (molar mass = 58.44 g/mol), how many grams of NaCl do you need?
6.05g
What is the principle behind the streak plate method that causes the microbial population to decrease with each successive quadrant?
The principle behind the streak plate method is mechanical dilution.