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Bacterial Morphology Essay

Question A and C answers.

A wet mount stain is when a drop of water is placed onto the microscope slide. The water on the slide helps to support the organism and sample. The water fills the space between the cover slip and the slide. This action allows the light from the microscope to pass through the slide and the sample for better visualization of the organisms. A direct stain occurs when a charged color portion of a basic dye like methylene blue combines with the negatively charged portion of and organism allowing the bacterium to become directly stained. In direct staining, the organisms must be fixed by a process such as heat. Fixing the slide prevents the organism form washing off the slide before visualization. This is accomplished by passing a smear of the bacteria through flame. The heat sets the proteins of the organism thus causing the bacteria to attach to the slide. The organism can become damaged from the setting process and the use of heat prior to staining. In indirect staining, the negatively charged colored portion of an acidic dye is repelled by the negatively charged bacterial cell wall. This causes the background to be stained while leaving the organism’s cell wall to remain colorless and unstained.

Question B answers

Specific bacterial morphologies noted in exercise one come from the spiral bacteria sample. The shape appears to be corkscrew in nature and vary in length throughout the sample slide. The length varies but the width seems to be uniform. The color most likely arises from the stain used to allow for better visualization of the organism. The Bacillus sample has no discernable morphology and appears as round ended, and cylindrical shaped in nature. The organisms have a black tint which is probably related to the type of statin used for visualization of the organism.

Question C Bullet 1

The direct smear sample and the indirect smears shown were different in appearance based on the staining method. The Direct Smear stained slides showed that the cells picked up the dye and were stained for better visualization as well as for differentiation of organisms viewed. The Indirect smears showed visualization of organisms and cells unstained and were visually different from the direct smear.

Question D

The plaque smears are somewhat circular in areas and irregular in other areas. The appearance is unlike the yeast slide. The plaque smear cells appear to contain a discernable nucleus which is absent in the yeast slide. The yeast smear shows uniformity in the shapes and sizes of the sample provided. The plaque smear shows irregularity in shape but a significant difference in the size of the sample cells provided.

Question E

I was unable to obtain an oral swab from my cheek but was able to visualize the slide provided and base my response on it. The cheek smear sample shows cells that are irregular in shape and in size. The cells appear to have a darker center which is located in differing regions from cell to cell. The samples appear to be clustered in together and tightly packed. The plaque smears are circular in areas and are in differing patterns and shape compared to the cheek cells. The plaque smears are round and differ in size. The cheek cells are differing in shapes and packed close together.


Hands-on-Labs. (2012). A Laboratory Manual of Small-Scale Experiments for the Independent Study of Microbiology. Englewood, CO. Available from www.labpaq.com

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