Essay on Unknown Rport on Bacillus cereus

2876 Words Oct 27th, 2013 12 Pages
Identifying the Unknown Bacteria: Bacillus cereus
Brittany Moy
Coastline Community College

Bacillus cereus is a Gram-positive, facultative aerobic, spore-forming, rod-shaped bacterium that is widely distributed among the environment.
The reason for identification of unknown bacteria was to help students recognize different bacteria through different biochemical tests and characteristics. This is important in the medical field because identification of unknown bacteria can help treat a patient by knowing the contributing source of a disease. Also, knowledge of different bacteria helped others make antibiotics that are used today.
Bacillus cereus, a commonly occurring pathogen which can
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Figure 1 Bacillus cereus simple stain
Next I performed a negative stain on my unknown sample. The negative stain is an extension of the simple stain, but uses an anionic chromophore (acidic) instead of a cationic (basic) one. Therefore the background will stain but the cell will not. No heat fixing is used in this technique so the cells remain alive on the slide. The sizes of the cells are more accurate with negative staining because the cells do not shrink as they do when they are heat fixed. Figure 2 Negative stain on B. cereus Lab Day 3: In order to identify the cell wall type, I performed a Gram Stain. Gram positive cell walls are composed of a thick layer of peptidoglycan and teichoic acids, while Gram negative cell walls have two lipid bilayers that sandwich a thin layer of peptidoglycan. After observing my slide under the microscope I determine that my unknown bacteria #745 is a Gram positive bacteria because the cells were a purple color. This happens because when the decolorizer (Ethanol or acetone) is added to Gram positive cells, the thick layer of peptidoglycan is dehydrated and becomes more compact. This ends up trapping the Crystal violet stain in the cell and therefore the cell remains purple. Figure 3 an example of B. cereus that has been Gram stained Lab Day 4: To determine whether my unknown bacteria produced endospores I needed to perform an endospore stain. An actively growing and metabolizing bacterium is

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