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
The Oxidase 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 Trypticase Soy Agar Plate. After the plate 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. A positive Oxidase test would have changed color to purple after three drops of the p-aminodimethylaniline Oxalate reagent were added, which indicated the organisms ability to produce cytochrome oxidase (Pearson’s 2011). If the test were negative there would be no color change after three drops of the p-aminodimethylaniline Oxalate reagent were added, which indicated no oxidase activity (Pearson’s 2011).

Bile Esculin The Bile Esculin test was used to test only the Unknown Gram-positive bacteria.
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).
Indole The Indole test was used to test only the Unknown Gram-negative bacteria.
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).
Citrate The Citrate test was used to test only the Unknown Gram-negative bacteria. One colony from the Unknown 13B plate was used to inoculate Simmons Citrate Slant. After the slant was inoculated, it was placed in an incubator at 37ºC for 48 hours. If the Citrate were positive, the agar would have changed color to blue, which indicated the presence of sodium carbonate (Pearson’s 2011). If the Citrate test were negative the agar would not have changed color, which indicated no presence of sodium carbonate (Pearson’s 2011).

RESULTS The Gram-positive bacterium for Unknown 13A was Staphylococcus aureus. Unknown 13A had similar reactivity to S. aureus. A comparison of Unknown 13A and S. aureus can be compared in Table 1. For the Catalase test, Unknown 13A and S. aureus were both positive (Table 1). The results for the Methyl Red tests were opposites; the Unknown 13A bacteria reacted negatively and S. aureus reacted positively (Table 1). For the Unknown 13A and S. aureus, Lactose, Sucrose, and Glucose Ferment tests all reacted positively, and no gas bubble was produced (Table 1). Positive testes for Unknown 13A and S. aureus were obtained in the Nitrate Reduction test and the Urea test (Table 1). For the Oxidase test, Unknown 13A and S. aureus were both negative (Table 1). For the Bile Esculin test, growth with a slight brown color was apparent in both Unknown 13A and S. aureus (Table 1). Unknown 13A and S. aureus both produced growing cultures that tested positive for the Mannitol Salt Agar test (Table 1).