According to Table , Escherichia coli and Proteus vulgaris showed fermentative activity. However Proteus vulgaris only showed it for glucose, while E.coli showed it for all three of the carbohydrates. Pseudomonas aeruginosa showed no fermentation. In table 3, the only bacteria which showed a production of indole was Escherichia coli. This is because E. Coli has the enzyme tryptophanase that can degrade the amino acid tryptophan into indole, pyruvic acid and ammonia. (Madigan and Thomas, 2009)The idole produced by the bacteria binded with the p-dimethlyaminobenzaldehyde in the reagent to produce the red compound.
(Madigan and Thomas, 2009) In table 5, the Proteus vulagris was the only positive bacteria for the urease test.
This means that Proteus vulagris is a rapid urease-positive organism. The restrictive amount of nutrients coupled with the use of pH buffers prevent all but rapid urease-positive organisms from producing enough ammonia to turn the phenol red pink. (Madigan and Thomas, 2009) The Urease broth can be used to differentiate members of the genus Proteus.
In table 7, the proteus vulgaris is the only positive bacteria.
The reason for this result is that Proteus Vulgaris is positive in the hydrogen sulfide test because it can undergo anaerobic respiration using Sulfur as an electron acceptor. (Madigan and Thomas, 2009)In table 9, Bacillus subtilis showed positive result on the starch hydrolysis whereas Escherichia coli did not. Starch hydrolysis requires the presence of exoenzyme amylase to hydrolyze starch into smaller polysaccharides. (Madigan and Thomas, 2009)
Positive result of starch hyrdrolysis showed the ability of the mircoorgism to produce amylase.
In table 11, showed that all of the bacteria are capable of producing catalase. Hydrogen peroxide is an superoxide which is able to be degraded by catalase. All of the bacteria where able to produce the enzyme to degrade it. In the oxidase test only Pseudomonas aeruginosa had a positive result. This is because it is the only microorganism out of the others which has oxidase.
This means it takes part in cytochrome oxidase activity. Oxidase activates the oxidation of reduced cytochrome c by molecular oxygen in aerobic organisms during electron transport. (Madigan and Thomas, 2009) Oxidized cytochrome c transfers molecular oxygen to tetramethyl-p-phenylenediamine when the reagent is added to growth of an oxidase positive organism. (Madigan and Thomas, 2009)
This experiment has the possibility of human error. Mistakes could have been made by failing to sterilize the inoculating loop correctly, which would result in possible contamination of the sample. Another error could have been possibly occurred by mislabeling the plates according to species, which would produce invalid results.
In conclusion the experiment was successful. I learned to distinguish species of bacteria by cultivating in different media and doing some tests. I also practised the proper techniques of testing for fermentation of carbohydrates, production of indole, activity of urease, production of hydrogen sulfide, evidence of amylase activity, evidence of lipase activity, and evidence of protease activity.
Department of Biology, 2010, Biology 130 Fundamentals of Microbiology Laboratory Manual. University of Waterloo, Waterloo pp. 23 – 32.
Goldman, Emanuel, and Lorrence H. Green. Practical Handbook of Microbiology. Boca Raton: CRC, 2009. Print.
Madigan, Michael T., and Thomas D. Brock. Brock biology of microorganisms . 12th ed. San Francisco, CA: Pearson/Benjamin Cummings, 2009. Print.
“Observing Plates.” Biology @ Davidson. N.p., n.d. Web. 12 Nov. 2010. <http://www.bio.davidson.edu/people/dawessner/302/302Lab3.html>.