Free Essays, Term Papers, Research Papers at Anti Essays

Casein Test
This test is to determine if an organism can produce the exoenzyme casease. Casease is an exoenzyme that is produced by some bacteria in order to degrade casein. Casein is a large protein that is responsible for the white color of milk. For this test we need to inoculate 1 skim milk agar plate with the bacterium, incubate the plate in an inverted position at 35°C for 28 to 48 hours. If an organism can produce casein, then there will be a zone of clearing around the bacterial growth called zone of proteolysis or hydrolysis. If clear zone is not present it is a negative test for casein. For unknown no.62, a zone of hydrolysis was present showing a positive test for casein hydrolysis.
Citrate Utilization
This test is performed to see if certain bacteria will use Citrate as their carbon source. The Citrate Agar Slant contains Sodium Citrate as the carbon source, Ammonium Phosphate as the nitrogen source and Bromthymol blue as the pH indicator. If the bacterium possess Citrase-permease, this molecule will transport the citrate into the bacterial cell and produce Pyruvate (Pyruvic Acid). Bromthymol blue is green at a pH of 6.9 or less. Bromthymol blue(ph indicator) is blue at a pH of 7.5 or greater. If a bacterium uses citrate as it’s carbon source, it will use the enzyme Citrase to degrade the citrate and the bacteria will also convert the Ammonium Phosphate to Ammonia and Ammonium Hydroxide. Both of these molecules will cause the agar to become alkaline and produce a royal blue color as they raise the pH of the slanted agar to alkaline. To test citrate utilization we need to inoculate a Simmons citrate agar slant with the bacterium (after washing it with sterile saline), incubate cultures for 24 to 48 hours at 35 °C. If medium changes color from green to blue it is a positive test for citrate, if there is not a color change and therefore no growth it is a negative test.
No color change was appreciated for unknown...