The pH changed twice, because initially, the bacteria were using sucrose as a source of carbohydrate fermentation, which resulted in the production of organic acids. The production of organic acids creates an acidic environment, which will turn the phenol red indicator to a yellow color. After an additional three days of incubation, the bacteria may have used up their carbohydrate supply of sucrose, and had to use other nutrients within the agar for their metabolism, such as amino acids and proteins. The result of using protein for metabolism, instead of carbohydrates is, alkaline waste products will be produced, creating a basic environment, which will turn the phenol red indicator to a pink color. You enjoyed microbiology so much at RVC, that you decided to become a microbiology professor. You are grading the last three unknown reports from your students. Which conclusion will receive the highest score?
A. Unknown #60 is Enterobacter aerogenes because it matched five of the seven tests, which was the best match. The last tests probably had a mistake.
B. Unknown #65 was a gram negative bacillus, was positive for glucose fermentation with gas production, negative for sucrose fermentation and postitive for lactose and mannitol fermentation. It was also negative for gelatinase, negative for hydrogen sulfide production, negative for urease. It was also positive for catalase, negative for oxidase and negative for DNase. This all matches the profile of E. coli.
C. Unknown #70 was a gram negative bacillus as shown in Table 1. This result narrowed down the options to; E. aerogenes, P. vulgaris, and E. coli. Unknown #70 was negative for esculin hydrolysis (Image 3) which eliminated E. aerogenes. The urease test, #70 was positive (Table 6), eliminating E. coli as an option. The only remaining option was P. vulgaris, resulting in the conclusion that Unknown #70 must be P. vulgaris.
D. Many tests were run on Unknown #75. Most of the tests were right, but some were contaminated and had the wrong results. When you compare the results of Unknown #75 to S. aureus in Table 10, you can see that they match almost all the tests. The tests that didn't match should have been performed again to get better results.
Triple Sugar Iron Results:
1) Gas (+, -)
2) Glucose (+, -)
3) Lactose (+, -)
4) Sucrose (+, -)
5) H2S (+, -)
Sulfur Indole Motility Results:
1) H2S (+, -)
2) Indole (+, -)
3) Motility (+, -)
Litmus Milk Results:
1) Acid (+, -)
2) Alkaline (+, -)
3) Curd (+, -)
4) Proteolysis (+, -)
5) Litmus Reduction (+, -)
6th EditionDavid L Nelson, Michael M. Cox
5th EditionCharlotte W. Pratt, Donald Voet, Judith G. Voet
9th EditionCain, Jackson, Minorsky, Reece, Urry, Wasserman
2nd EditionDavid E. Sadava, David M. Hillis, H. Craig Heller