One Another by Their Morphology

1 January 2017

Bacteria can be distinguished from one another by their morphology (size, shape, and staining characteristics). In this lab experiment, bacterial morphology was examined by observing both stained and unstained organisms. A wet mount is a preparation process where a live specimen in culture fluid is placed on a slide and the organism is free to move about. In the wet mount slides provided via LabPaq software with cheek, dental plaque, and yeast specimens were observed.

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The wet mount preparations were difficult to observe because of poor contrast, however, a common occurrence in the specimens were cells large in size and translucent in color. The slides provided with direct staining using crystal violet gave the most imagining of morphology. The directly stained cells gave off a purplish hue to the cells, making them easier to visualize and classify. The indirect specimens stained with congo red provided translucent cells while others were a brownish red, however, the cellular characteristics were easily distinguishable.

There was no experiment provided in which indirect staining using both congo red and crystal violet was undertaken. It may be hypothesized therefore that in this case one may observe both red and purple stains of cells depending upon the negative or positive component of the cell. Staining enhances the visualization of smears and reveals differential characteristics such as morphology. As stated previously, utilizing a wet mount prepared slide, the specimens were difficult to visualize. However, using the staining methods, specific bacterial morphologies were identified.

For example, at 100x, a direct stain of yeast returned a cluster of cocci. A stain is a chemical that adheres to structures of the microorganism and in effect dyes the microorganism so the microorganism can be easily seen under a microscope. Stains used in microbiology are either basic (direct) or acidic (indirect). Basic dyes are used for positive or direct staining and the specimen is stained while the background remains clear. Indirect staining is preparing colorless bacteria against a colored background. Acidic dyes are used for negative staining.

In the experiments, the smears in each type of staining did not appear different in each type of staining. For example in the direct stain of the check, the cells appeared irregularly round shaped with a nucleus. With the indirect stain, the cheek cells had the same appearance as in the direct stain. The smears were the same, with only enhanced contrast due to staining. This is because staining whether direct or indirect does not change the appearance of the smears, only improves the images. This explains why the smears did not appear different in each type of staining.

When observing the cells in the plaque and those in the yeast smears, it can be noted that both contain cocci, however, the cocci in the plaque smears were in chains, whereas the cocci in the yeast smears were in clusters. The cells seen in the smear from the mouth smear yielded large, flat, irregularly shaped cells that contained a nucleus. The cells appeared to be independent of other cells and scattered about. The irregular flat shape of the cell may predict the function of this cell to protect and propel foreign substances to the back of the mouth.

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