Microbiology Unknown Paper

1199 WordsApr 19, 20145 Pages
The purpose of this laboratory exercise was to perform tests necessary to be able to distinguish one microorganism from 10 others. Using a series of biochemical tests and characteristics, unknown #22 was concluded to be Pseudomonas aeruginosa. A dichotomous key was mapped out and used during this process. Using this provided guidance as well as organization as to what the result may be. Upon obtaining the unknown organism, it was important to make a streak plate of the bacteria on TSA. The purpose of doing so ensures that we have pure cultures of the unknown to be used in further testing and not a mixed culture. The first test used was a gram stain. It is a differential stain that helps distinguish between gram-positive and gram-negative…show more content…
There was also motility because there was growth away from the point of inoculation. It looked like an upside down Christmas tree in the tube. The last thing SIM tested for was indole production. It is produced when the bacteria converts amino acid tryptophan to indole. 5 drops of dimethylaminobenzaldehyde, or Kovacs reagent, was added to the test tube. Upon addition, if it is positive for indole, it will turn a red color at the top of the medium. When the unknown was tested, it did not produce a red color. There was a slight dark red/brown color, but overall the test result was negative. Lactose and sucrose tests were done, which are very similar to the glucose test. The only difference is the 1% carbohydrate in the medium. For sucrose, the medium contained sucrose. For lactose, the medium contained lactose. Both of the test tubes resulted in a K result. There was no color change to yellow or any gas produced in the inverted test tube. The color did change to an unusual bright pink, but it did not turn yellow like it would have in the presence of acid. The unknown was also tested for catalase. Aerobic bacteria produce the enzyme catalase. It breaks downs hydrogen peroxide into water and oxygen. After smearing an isolated colony of the unknown on a slide, hydrogen peroxide was added and it resulted in bubbling. Bubbling suggests a positive test and if there is no bubbling, it is a negative test. A citrate lyase test was also done using citrate agar. Bacteria
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