13a Test Lab Report

The Urea test was used to test both Unknown Gram-positive and Unknown Gram-negative bacteria. One colony of bacteria was used from the Unknown 13A plate and Unknown 13B plate in order to inoculate the Urea Slant. After the slant was inoculated, the cultures were placed in an incubator at 35ºC for Gram-positive bacteria, and 37ºC for Gram-negative bacteria for a total of 48 hours. If the Urea test were positive, the color of the slant would have changed to a hot pink color, which indicated the bacteria’s ability to produce urease, and the presence of ammonia (Pearson’s 2011). If the Urea test were negative, the color of the slant would have stayed the same, which indicated that the bacterium was unable to produce urease (Pearson’s 2011).

Oxidase
One colony from the Unknown 13A plate was used to inoculate the Bile Esculin Slant. After the slant was inoculated, it was placed in an incubator at 35ºC for 48 hours. A positive Bile Esculin test contained a black precipitate throughout the slant, which indicated the bacterium was able to hydrolyze esculin to esculetin and glucose (Pearson’s 2011). A negative Bile Esculin test would not have a black precipitate, which indicated that the bacterium was unable to hydrolyze esculin (Pearson’s 2011).

Mannitol Salt Agar The Mannitol Salt Agar test was used to test only the Unknown Gram-positive bacteria. One colony from the Unknown 13A plate was used to inoculate the Mannitol Salt Agar Plate. After the plate was inoculated, it was placed in an incubator at 35ºC for 48 hours. If the agar surrounding the culture changed from red to yellow the test was positive, which indicated that the bacterium was capable of fermenting mannitol (Pearson’s 2011). If the agar surrounding the culture did not change color the test was negative, which indicated that the bacterium was unable to ferment mannitol (Pearson’s 2011).
One colony from the Unknown 13B plate was used to inoculate the Tryptone Broth. After the broth was inoculated, it was placed in an incubator at 37ºC for 48 hours. A positive Indole test would have turned red after the addition of ten drops of Kovac’s Reagent to the culture, which indicated tryptophan was hydrolyzed (Pearson’s 2011). A negative Indole test would have turned yellow after the addition of ten drops of Kovac’s Reagent to the culture, which indicated that tryptophan, was not hydrolyzed (Pearson’s 2011).

H2S Production The H2S Production test was used to test only the Unknown Gram-negative bacteria. One colony from the Unknown 13B plate was used to inoculate a SIM Agar Deep Tube. After the culture was inoculated, it was placed in an incubator at 37ºC for 48 hours. A positive H2S Production test would have showed a black precipitate along the stab line in the media, which indicated that ferrous ammonium sulfate combined with gas to form the black precipitate (Pearson’s 2011). A negative H2S Production test would have showed no black precipitate along the stab line in the media (Pearson’s 2011).