Lab Practicum Flashcards
Organisms that grow at 37o
Mesophiles
Organisms that grow at 25o
Psychrotroph
Reasons for lack of growth on plates
Incorrect atmosphere: inadequate temp, oxygen, growth factors
Or even TSA too rich
Microscope part that focuses light
Condenser (light down = resolution down)
Knobs on microscope
Fine focus, coarse
Looking at bacteria under microscope
Oil immersion lens, full light, fine focus knob
Adjust scope for live organisms
Prepare wet mount with cover slip, so not use oil immersion lens, reduced light
Examples of simple stain
Indian ink, crystal violet, safranin; used to observe cell shape and arrangement (cell walls are negatively charged and dyes are positive)
Gram stain steps
- Crystal violet- dye(30)
- Mordant - Iodine (60)
- Decolonizer - Alcohol (5-30)
- Counter stain safranin (60)
Reasons Gram + show Gram -
- Iodine left on too long
- Too much decolonizer
- Samples are older and can’t retain crystal violet
Why not stain acid fast?
Waxy cell wall doesn’t retain staining
What is aseptic technique
Free of contamination: Procedure that prevents introduction of unwanted microbes
Pure colony
A group of cells descendent from a single organism and free of contamination
How to determine the number of organisms in a culture (by looking at a plate)
organisms on plate/mL original sample * dilution
Calculate the dilution ***
Dilution = sample (mL)/(diluent+sample)
