Carbohydrate Fermentation Test
Essay by Nurul Sabrina Mohd Shafie • April 12, 2017 • Lab Report • 740 Words (3 Pages) • 2,588 Views
Results:
Carbohydrate fermentation test
Fermentation test | Bacterium | |
Escherichia coli | Bacillus subtilis | |
Lactose | positive | positive |
Glucose | positive | positive |
Sucrose | negative | positive |
[pic 1]
Figure 1 showed the result for carbohydrate fermentation test of Escherichia coli.
[pic 2]
Figure 2 showed the result for carbohydrate fermentation test of Bacillus subtilis.
Indole test
Bacterium | Observation |
Escherichia coli | positive |
Bacillus subtilis | positive |
[pic 3]
Figure 3 showed the result of indole test for both bacteria.
Voges-Proskaeur Test
Bacterium | Observation |
Escherichia coli | negative |
Bacillus subtilis | negative |
[pic 4]
Figure 4 shows the result of Voges-Proskaeur test for both bacteria.
Citrate test
Bacterium | Observation |
Escherichia coli | negative |
Bacillus subtilis | negative |
[pic 5]
Figure 5 shows the result of citrate test for both bacteria, E. coli(left) and B. subtilis(right).
Catalase test
Bacterium | Observation |
Escherichia coli | positive |
Bacillus subtilis | negative |
[pic 6]
Figure 6 shows there is appearance of gas bubbles which indicates a positive test for
E. coli.
Discussion:
In this experiment, we conducted some biochemical tests which are carbohydrate fermentation, indole, Voges-Proskaeur, citrate, and catalase tests. All of these test were performed to identify the microorganism. Based on our result, we got the accurate result for both bacteria for the carbohydrate fermentation test. In this test, the phenol red used which act as an indicator is initially neutral (pH 7). As we can see in the figure 1 and 2, all the medium in the tubes change into yellow colour except for the sucrose broth tube that was inoculated with Escherichia coli (E. coli). The changes in colour showed that the organism ferment carbohydrates caused acidic organic by product to accumulate and turn the medium to acidic.
Next for the indole test, it is performed to test the ability of organism to break down tryptophan to indole. A positive result is shown by the presence of red ring in the layer of the broth. Based on the theory, only bacteria E. coli will have positive result. However, according to our result (Figure 3) bacteria Bacillus subtilis (B. subtilis) also showed a positive result. This is may due to error in inoculating process. The medium may be contaminated with other microorganism which will affect the result.
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