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An experiment to demonstrate bacterial staining.

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Liverpool John Moores University in Association with St Helens College Franchise Degree of B.Sc. (Hons) Applied Biology Basic Microbiology An Experiment to Demonstrate Bacterial Staining Assignment 1 Introduction If bacterial colonies are measured to be between 1mm to more than 1cm, then it is obvious that the individual microbe is a lot smaller. In this experiment to observe the microbes more thoroughly, techniques that were founded, tried and tested many years ago such as various staining techniques, were used to observe the individual microbes in this experiment for their characteristics, and with the aid of a light microscope this was possible. The purpose of staining in microscopy is to: - Add contrast to the image Identify chemical components of interest Locate particular tissues, cells or organelles. The three techniques carried out in this experiment; namely Gram Staining, Endospore Staining and the Hanging Drop; shown characteristics like size, form, elevation, colour and motility. Even under light microscopy (conditions better than the human eye), the bacterium portrayed clearer once it had been stained. Microbial characteristics have in the past proved to be of importance to mankind, having the knowledge regarding bacteria created many medicinal uses, such as the production of antibiotics and led to great advances in finding cures for deadly diseases, using the Gram staining method which ...read more.


It is too thin to retain most of the crystal violet-mordant complex, but it could retain the safranin counterstain, so gram negative cells stain red. As shown in the results Escherichia coli was stained red this enabled a conclusion that E-coli is a Gram negative bacteria. The space between the peptidoglycan layer and the outer membrane is called the periplasm and it contains many different proteins. The outer membrane also contains porins, which are proteins that form pores in the membrane and allow small hydrophilic molecules to pass into or out of the cell. Hydrophobic or larger molecules cannot pass through the porins and this is how the Gram stain is prevented from reaching the peptidoglycan layer to colour it. Endospore Method The results conclude that Escherichia coli do not produce endospores yet Bacillus subtilis do. The endospores were seen as oval blue/green structures, and the red rods were classified young vegetative cells. Unique to bacteria endospores are highly resistant dehydrated cells with thick walls and additional layers. The thick wall consists of two membranes containing peptidoglycan, a thick spore coat that contains proteins which form around the membrane thus enabling the endospore to be highly resistant. ...read more.


When the flagella are all rotating counter clockwise, the flagella are bundled together and the bacteria travel in a straight line (i.e. it swims). When one flagella switches direction the bundle disassociates, and the bacteria tumbles, alternative swimming and tumbling results in a three-dimensional random walk. Chemo-attractants and repellents can interaction with receptor proteins in the cell envelope, which influence the rate of tumbling when the cell is moving in a given direction. An electron microscope would have shown a more detailed motility, as this was not available the results did not show as many of these facts stated in this conclusion. Not all microorganisms get around by using bacterial flagella. Eukaryotic microbes will use flagella, but they are larger and more complex than bacterial flagella. Also, other bacteria use gliding motility that depends upon contact with a solid surface. Under the microscope it seems as if they are sliding along the surface. Enterobacteriaceae (Enterics) Include a group of bacteria that inhabit the intestinal tract of humans and other animals. They include motile and nonmotile species; those that are motile have peritrichous flagella. The facultative anaerobic E. coli is one of the most common inhabitants of the intestinal tract. It is not usually pathogenic; it can be a common cause of urinary tract infections and can also cause "traveller's diarrhoea". ...read more.

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