Purpose To identify an unknown microorganism by performing a series of biochemical tests on a pure bacterial culture.
Materials and Methods 1. One test that was used to discover the identity of the given bacterial culture was the carbohydrate utilization tests. This specific set of tests involved two broths, namely phenol red lactose and phenol red sucrose, and a Durham tube placed upside down in the broth tubes. These broths can be broken down by fermentation processes, which produce an acid, gas or both. The broth tubes also contain a pH color indicator, which changes color to indicate if acid has been produced. The pH indicator will turn from a red to yellow, indicating a positive result. A negative result is indicated by no color change or a change to deep magenta if ammonia is produced. Another form of a positive result is the formation of a gas bubble in the Durham tube. This result will usually occur along with the acid …show more content…
The sulfide production test was also used to find out the identity of the unknown bacteria. When amino acids cysteine and methionine are decomposed, they produce hydrogen sulfide gas. Certain bacteria produce the enzymes necessary to break down those two amino acids and a simple stab test can be done to see if the bacterium is present. A sulfite indole motility medium is utilized for this test and stabbed with inoculated bacteria. A positive result would be a black precipitate at the bottom of the medium. 5. Another test used was the urea hydrolysis test. This test utilized the enzyme urease, which some bacteria produce. This enzyme breaks urea into ammonia and carbon dioxide. A urea broth tube containing a phenol red indicator is inoculated with the bacteria. When ammonia accumulates in the tube, the environment inside the tube becomes very alkaline. A positive result occurs when the liquid in the tube turns a bright magenta. A negative result would remain the tan color or turn slightly
Materials and Methods 1. One test that was used to discover the identity of the given bacterial culture was the carbohydrate utilization tests. This specific set of tests involved two broths, namely phenol red lactose and phenol red sucrose, and a Durham tube placed upside down in the broth tubes. These broths can be broken down by fermentation processes, which produce an acid, gas or both. The broth tubes also contain a pH color indicator, which changes color to indicate if acid has been produced. The pH indicator will turn from a red to yellow, indicating a positive result. A negative result is indicated by no color change or a change to deep magenta if ammonia is produced. Another form of a positive result is the formation of a gas bubble in the Durham tube. This result will usually occur along with the acid …show more content…
The sulfide production test was also used to find out the identity of the unknown bacteria. When amino acids cysteine and methionine are decomposed, they produce hydrogen sulfide gas. Certain bacteria produce the enzymes necessary to break down those two amino acids and a simple stab test can be done to see if the bacterium is present. A sulfite indole motility medium is utilized for this test and stabbed with inoculated bacteria. A positive result would be a black precipitate at the bottom of the medium. 5. Another test used was the urea hydrolysis test. This test utilized the enzyme urease, which some bacteria produce. This enzyme breaks urea into ammonia and carbon dioxide. A urea broth tube containing a phenol red indicator is inoculated with the bacteria. When ammonia accumulates in the tube, the environment inside the tube becomes very alkaline. A positive result occurs when the liquid in the tube turns a bright magenta. A negative result would remain the tan color or turn slightly