In this experiment that we performed, there were many methods that were used to help us manipulate and identify the bacteria E.coli on a MacConkey agar plate. The first part of the experiment involved the methods of manipulating, identifying and counting the bacteria and the second part was to find out whether the bacteria E.coli was the only type found in the given area by gram staining.
E.coli was the chosen bacteria for this type of experiment. It is a gram negative bacterium that will grow rapidly given ‘any culture medium with the necessary energy source, nutrients, pH, and temperature’. Therefore, MacConkey Agar being the medium for its growth will enable us to achieve the experiment outcome.
MacConkey Agar only allows the growth of gram negative bacteria as they do not contain bile salts and crystal violets. This was chosen because it groups bacteria on the basis of colour so therefore will make it easier to determine its type. It contains a pH indicator which is its red colour and also a disaccharide called lactose. This makes the area rich enough for the E.coli bacteria to find it easy to adapt to the environment.
Some of the methods that were used in part A were streak plating, viable plate counting, spread plating and serial dilutions. Streak plating involves continuous dilution of the bacteria spread over the surface of the Agar plate using the loop. As the bacteria space out, some multiply and form individual colonies over a period of time. When pure coloured strain of colonies are seen, it means that more than one bacterium is involved. However, if one distinct type of colony is seen then only one type of bacterium is being used which is the result that we expected.
Viable plate counting which a method is used to determine the number of cells was also used. A solution that doesn’t alter the growth or decrease of the bacteria is diluted into a tube of the sample. The dilution has to be done in many tubes
References: for API 20E tests • Qinn P.J, Carter M.E, Markey B, Carter G.R. Clinical Veterinary Microbiology (1994) Elsevier Limited • http://www.suite101.com/content/api20e-bacterial-id-test-strip-a55408 • http://www.helium.com/items/1482721-api-bacteria-identification