Lab Final Flashcards
Micrococcus Luteus
Gram + cocci; No growth on HE and EMB agar; Clusters
Spores form on
Gram + rods
Spores appear
clear or light blue
Staphylococcus epidermidis
Gram + cocci; No growth on EMB agar; grape like clusters
Escherichia coli
Gram - rod; Lactose fermenter on HE and EMB agar; coliform
Bacillus subtilis
gram + rod; spores
- Crystal violet
1-2 minutes
- Gram’s Iodine
1 minute
- Acetone-alcohol
1-2 seconds
- Safranin
1-2 minutes
The primary stain
Crystal violet
The mordant
Gram’s iodine, a reagent that sets the dye in the tissue or cell
The decolorizer
Acetone-alcohol
The counterstain
Safranin
Saccharomyces cerevisiae
Gram + cocci; buds
EMB agar
Eosin Methylene Blue Agar (Red)
HE agar
Hektoen Enteric Agar (Green)
EMB agar is differential because
it allows fermentation (color change of the agar)
EMB agar is selective because
gram + bacteria cannot grow there. It is selective for gram - organisms.
HE agar is slective because
Gram + organisms cannot grow there. It is selective for gram - organisms.
Metallic green on EMB agar means
the organism is a lactose fermenter
HE fementating carbohydrates
lactose, sucrose, and salicin
Why is the immersion oil added to the microscope?
the oil acts as an additional lens in the system and prevents the loss of necessary light rays.
simple stain
-The bacteria is stained with one dye and subsequently, the bacteria will all be the same color
Gram stain is based on
cell wall composition
Why you should allow the smear to air dry? why you cannot use heat to do this?
- because the slide is allowed to sit until it has no longer appears moist
- If heat is used to speed up the drying process, the cell wall of the organisms may be distorted or rupture and release the cyrstal violet dye when it should retain it
By adding the de-colorizer after the mordant, what color would you think the cells would be?
The gram positive cell would be PURPLE.
The gram negative cell would be CLEAR.
What is the difference between gram positive and gram negative?
- Gram negative have an outer membrane, and they also have a thin peptidoglycan. Gram positive on the other hand, do not have an outer membrane, and have a very thick peptidoglycan
- The Gram-positive cells have thick walls, and they will retain the purple crystal violet stain if decolorization was carried out correctly. The Gram-negative cells will be decolorized and are colorless. Watch the video to review the effect of decolorization on both types of cells.
In cells, the gram reaction depends on what?
Their gram reaction depends on their cell wall composition.
