Example of Microbiology Unknown Lab Report

By at January 16, 2014 | 12:39 pm | Print


Alexis Welker

Biology 203



An important part of medical treatment is the bacterial identification. Many treatments are dependent on the identity of the microbe causing the problem. Once the microorganism is isolated scientist are able to examine its structures and determine how it is able to function.  Bacteria are mostly known for causing disease or harming the health of humans, but not all bacteria should be considered like this. There are some that are essential for our existence and to keep our food chain from collapsing. Other bacteria have been beneficial to humans; that are found in some of our favorite foods. Being able to culture, isolate and identify a unknown bacteria is one of the corner stones in microbiology BIO 203, as well as the ability to use different techniques to distinguish and identify different bacteria.


Materials and Methods

An unknown labeled 123 was given out by the lab instructor. An isolation streak was done on a Nutrient Agar, and then was placed into an incubator at 37 degrees for two days to grow. Once the incubation was completed two different colonies showed growth on the the Nutrient Agar plate. The different colonies were then both isolated onto two different Nutrient Agar plates and placed into the incubator at the same temperature for another two days. After taken out of incubation both of the plates were labeled. One was labeled unknown streak A and the other was labeled unknown streak B. Then a gram stain was done to both unknown streak A and B. A microscope was then used to identify whether unknown streak B was a gram negative or gram positive. Unknown steak B had purple circles which was gram positive. Unknown streak A showed evidence of contamination during the gram staining process. A gram negative tube was given by the instructor and another gram stain had been done. Unknown streak A was red and had rods, therefore it was a gram negative. These tests were done and followed by the help of the McDonald lab manual.


Tabel 1 lists the test, purpose, reagents and results of Unknown streak A

All of the following tests were performed on this unknown

1)     Urea test

2)     Mannitol test


Table 2 list the test, purpose, reagents and results of Unknown streak B

All of the following tests were performed on this unknown

1)     Mannitol test

2)     Urea test

3)     Nitrate test


GRAM STAINTo determine the gram reaction of the bacteriumCrystal violet, iodine, decolorize, safraninRed/pink rodsGram negative rods 
UREADetects the enzyme ureaseUrea broth tubeColor changed to pinkPositive for Urea test 
MANNITOLTo determine if it produces acidMannitol broth tubeColor changed to a pinkNegative for producing acid 







Table 1: Unknown A


Table 2: Unknown B


GRAM STAINTo determine the gram reaction of the bacteriumCrystal violet, Iodine, decolorize, SafraninPurple circlesGram positive results
UREADetects for the enzyme ureaseUrea broth tubeColor changed to a red/orangeResults were negative
MANNITOLTo determine if it produces acidMannitol broth tubeBroth turned yellowPositive for producing acid
NITRATEBroth tube that tests for nitrate reductasesNitrate broth tube, Reagents A&B, zincNo results when reagents A&B were added, once zinc  was added broth changed to color redNegative results, zinc reduced any nitrate remaining in the tube.



Unknown A or also known as Proteus vulgaris was difficult to find. To start this process an isolation streak had to be done. Once the isolation streak had been done, several gram stains had been attempted, but since there were some contaminations in this process it made the bacteria a bit more difficult to find. After many contaminated gram stains the gram negative was given by the instructor in a test tube.  Finally a clear gram negative with rods has appeared on the slide. Using a sterile inoculating loop a few drops of Proteus vulgaris was taken placed in an Urea broth tube as well as a Mannitol broth tube. These tubes were incubated at 37 degrees for two days. After the incubation was completed the tubes were thoroughly examined. The mannitol test came out negative, because it failed in producing acid. The outcome of the Urea test was positive, because the color of the broth changed to pink. This is considered a positive reaction.

Unknown B or also known as Enterococcus faecalis was much easier to find than Unknown A. As the McDonald lab says the first step is an isolation streak. Once the isolation streak had been completed the next step would be a gram stain. The first try at this gram stain went perfectly, but just to be safe another gram stain was performed. The second gram stain came out much more clear and had better result. The results that were seen on the slide were a clear purple positive with circles as well as noticeable colonies. The next step was to use a sterilized inoculating loop that took a bit of Enterococcus faecalis and was dipped into a Urea broth tube, Mannitol broth tube and as well as a Nitrate broth tube. These test tubes were then placed in the incubator at 37 degrees for two days. The Urea test came back negative with no color change to the broth. The Mannitiol test had produced acid , which is considered a positive reaction. When the reagent A and B were placed into the Nitrate tube there was no change. Once a pinch zinc was added to the tube it immediately turned red which means it produced acid and that is a negative reaction. . All techniques and instructions done as laid out in the LAB MANUAL BIO 203 by MCDONLD.

Proteus vulgaris is found in human intestinal tract, soil, water and plants. These organisms usually do not grow well in the intestinal tract but can act as possible pathogens that cause infant diarrhea and 29% of all urinary tract infections. This bacterium has been connected with wound infections due to direct contact. This bacterium has also been linked to food spoilages, such as fresh meat, poultry, and seafood. This bacterium is actively motile and swarming behavior. In order to treat this bacterium you will need ampicillin and aminoglycosides. (Tortora, Gerard J. pg 311)


1)     Tortora, Gerard. J. Microbiology An Introduction eleventh edition. Glenview, IL, 2013, 2010, 2007. Print

2)     McDonald, Virginia. Lab Manual for General Microbiology. St. Louis Community college at Meramec. April 2011.



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