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Culturing Bacteria.

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Microbiology ~ Practical 1: Culturing Bacteria Chris Grocock 09/02/04 ~ Introduction Bacteria are microscopic organisms, consisting of one prokaryotic cell. They are relatively simple organisms, with no membrane bound organelle, and only one chromosome. They are quite versatile creatures, being able to survive in both solid environments and liquid (broth). When present on/in a nutrient rich medium such as agar gel, bacteria divide, doubling their population in as little as 20 minutes, forming small gatherings of cells known as colonies, often in circular patterns but also can be filamentous, irregular, spindle shaped, etc. It is possible to estimate the number individual bacterial cells on an agar plate using various dilutions of the bacterial liquid sample. In solid colonies, bacterial growth is greatest on the edge of colonies, growth being fairly slow/non existent in the centre. In broth cultures all cells are at the same stage of growth and same speed but it is almost impossible to estimate the number of bacterium in a broth culture. Bacteria live all around us, particularly in the air we breathe, when bacteria in the air come into contact with a growing medium such as agar, which has an ample supply of nutrients, they will colonise the area and reproduce. Leaving nutrient agar plates in the open air is a good way of demonstrating this process, but bacteria growth can also be manipulated by us. ...read more.


Their ideal temperature for growth is 37 degrees Celsius. When cultured on solid medium, it is known to produce cream white circular colonies. E.Coli bacteria, normally found in human stool, can exist as a non harmful strain or as a harmful strain, most commonly strain 157. Diseases of E.Coli include diarrhoea, which can be treated with anti-biotic, and meningitis. When grown on solid plates, E.Coli produces small yellow circular colonies. (www.grgreen.com, 2004) (www.sciencenet.com.au, 30/01/2004) (Prescott et al, 2002) ~ Method The method used was the same as the method described in the course module guide. The first method of streaking was as below. The second technique is shown below: The only unique thing was the style of streaking used for the last nutrient agar plate. For this plate, the "smiley face" technique was adopted to try and separate out individual colonies for the mixed culture. The method for this highly skilful technique is outlined below; * Using the aseptic technique (described in the introduction section), the inoculating loop was placed approximately one third of the way down the plate, and approximately one third inward, and streaked as indicated on the diagram (below). * This was done again on the opposite side of the plate, giving an "eye effect". * A similar sized streak was placed on the centre of the plate, giving a "nose" effect. ...read more.


The smiley face method adopted for the 3rd agar plate was not particularly effective at separating colonies. While a few creamy white colonies were distinguishable from the solid streaks, in the pattern known as "spots", the previous two methods were far more effective. Both the line and the snake methods were quite effective at separating out the E.Coli and the M.Leteus colonies. I believe the creamy white colonies to be M.Leteus, and I think that the line method is best at isolating this bacteria. I believe the snake method to be best at isolating the yellow colonies which I believe to be E.Coli. The liquid culture for M.Leteus was fairly clear before and after swirling. Before swirling the bacterium colonised the bottom of the glass container. Because of this, and because of a, much larger presence of M.Leteus on the agar, I conclude from this that M.Leteus is best adapted/"likes" solid media for growth rather that liquid media. The E.Coli was cloudy before and after swirling and produced slime which did not disperse after swirling. This seemed grow well in the liquid culture compared to M.Leteus and grew well on the solid agar, suggesting that it may be more versatile than M.Leteus. The soil sampled produced slime which was present before and after swirling. It also produced a surface layer before and after, and was cloudy before and after. I conclude from this that because of all the different things present, e.g. slime, surface layer, cloudiness, that more than one species of bacterium was present. ...read more.

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