Test Tube # 13 Lab Report

The following tests according to the lab manual were performed: gram stain, fermentation tubes, methyl red, vogues proskauer, sulfur, indole, motility and growing it up on MacConkey agar. The gram stain was performed incorrectly the first time. This is because the decolorizer was not on the bacterium slide for long enough, giving a false outcome.

The purpose of this lab was to identify an unknown bacteria culture using differential tests. The identification of the unknown culture was accomplished by identifying the bacteria based on its specific metabolic characteristics and morphology. It is suggested that culture 11 is a sample of Enterobacter aerogenes.

6. The disks in the 0.00% solution were transferred to an agar plate held next to the blue flame using the sterilized tweezers. Excess disinfectant was removed from the disks by wiping on the side of the well of the spotting tile. When the 5 disks were positioned (refer to Figure 1 below) the lid was replaced and sticky taped down. A label was added indicating the concentration of disinfectant.

The Gram stain was used to determine if the bacteria was gram positive or negative. A negative test shows a pink color and a positive test is a purple color. When a bacterium is negative it is because it has an outer membrane and a thin layer of peptidoglycan that is much harder to stain. A positive bacterium has a thick layer of peptidoglycan and no outer membrane that can be penetrated by crystal violet.

Next I performed a KOH test to further confirm that my organism was a Gram-negative species. For the KOH test, I added 3 drops of 10% potassium hydroxide (KOH) to a small drop of distilled water onto a clean microscope slide, transferred a visible clump of organism to the KOH solution using my inoculating loop. I than mixed the cells into the solution using small, circular motions for 60 seconds and then lifted up the loop to look for what appears to be a “stringing” affect which means it’s confirmed that it is gram- negative species. Next, I created a streak plate using nutrient agar so that I could see pure culture of my organism. I aseptically obtained a loop full of my organism and gently inoculated one quarter of the nutrient agar plate by running the loop back and forth across the surface. I then flame sterilized the inoculating loop, allowing it to cool for 10 seconds, and then streaked the organism from quadrant I into quadrant II using a zigzag motion technique. I repeated those steps streaking from quadrant II to quadrant III and then streaking from quadrant III to quadrant IV. Once completed, I put the streak plate in the incubator at 37° for 24-48 hours. 48 hours later, I check my streak plate and it had a lot of growth on it. I was able to determine that the organism was definitely an off white color, opaque. The IV quadrant was the quadrant that best

There are many reasons for knowing the identity of microorganisms. The reasons range from knowing the causative agent of a disease in a patient, so as to know how it can be treated, to knowing the correct microorganism to be used for making certain foods or antibiotics. This study was done by applying all of the methods that I have been learned so far in the microbiology laboratory class for the identification of an unknown bacterium.

2) Record the shape of the bacteria, the arrangement of the bacteria, and the gram staining characteristics.

Many tests were completed on the unknown such as gram staining and inspection under microscopes to find whether the bacterium is gram positive or gram negative. Chemical resistance tests were also performed to see if certain chemicals affected the unknown growth or if it didn’t affect the bacteria at all. Each biochemical test

This test is for only gram positive bacteria; unknown species B. Using a starch agar plate inoculate gram positive bacteria onto it. Make any kind of design on the starch agar. Label the plate starch agar and unknown species B. Incubate the starch agar for at least 48 hours at the 25C. After incubation open the agar plate and cover the entire surface with iodine and allow it to soak into the agar for 5 to 10 minutes. If there is a clear zone around the growth pattern or halo this means, there is no starch present and the bacteria have consumed the starch. Having a clear zone or halo means the test is

For tube B, I could have stopped at the first test conducted since my obtained result was unique to one bacteria. However, I wanted to perform a confirmatory test just to be certain of my assumption. In conclusion, my obtained results for both test tubes were identical to the expected results of the bacteria, so there were no inconsistencies. I was able to identify my unknown in tube 30A as E. faecalis due to a negative catalase test. The test indicates that E. faecalis was not able to produce catalase. Although S. epidermidis and M. luteus showed a negative result in the DAase test, as did E. faecalis, these two bacteria would yield a positive result in a catalase test. I was able to identify my unknown in tube 29B as E. coli due to a negative result in the citrate test. This means that E. coli was not able to utilize citrate as its sole source of carbon. Although P. vulgaris also yields a negative result in the citrate test, I was able to rule it out because it did not produce the intense, metallic green sheen on the EMB plate. I was able to rule out C. freundii as a bacteria because although it does produce a somewhat green sheen on the EMB plate, it would produce a positive result in the citrate test, which is not the result I

The bases of this experiment was to discover the identify of the unknown from three possible specimens: Klebsiella pneumonia, Escherichia coli, and Enterobacter aerogenes. Utilizaing the T streak technique, the bacteria was isolated into pure colonies for further study. The Gram Stain method was used to identity the morhphology of the bacteria such as the shape and whether the bacteria was Gram positive or Gram negative. Biochemical test were also used to help identify the unknown bacteria. The biochemical test used was the Triple Sugar Iron Agar, Sulfur Indole Motility test, Methyl Red test, Voges-Proskauer test, Citrate test, Urease test, and the Gelatin test. After observing the morphology of the bacteria using the Gram Stain method and utilizing all the possible biochemical test, the bacteria was identified to be Enterobacter aerogenes.

We examined the growth on each plate, which helped us determine whether our bacteria were Gram-positive or Gram-negative. Once we figured this out, we performed more testing to further differentiate our specific bacteria. The first test we performed was the Catalase test, which tests for the enzyme catalase. The substrate of catalase is hydrogen peroxide and when it is broken down water and oxygen are released. To test for this enzyme, we added one drop of 3% hydrogen peroxide to a microscope slide with a sample of our bacteria.

First, take the prepared slide of bacterial smear and examined it under the microscope in order to become familiar with the morphological types of bacteria. Once familiarized, initialed a microscope slide with a grease pencil. Then, place a drop of tap water on the center of the slide. Next, pick up a very small amount of

The initial test that I had performed was the Gram staining test. I conducted this test a total of three times for final results. The Gram staining test is performed to differentiate between the two major categories of bacteria: Gram positive and Gram negative. In other words, the procedure enables bacteria to retain color of the stains which is based on the physical and chemical properties of the cells wall. The basic four step process of gram staining are: Application of the primary Crystal Violet stain onto a bacterial culture that had initially been heat fixed. The positive CV ions interact with the negatively charged bacterial components and happen to stain the bacterial cells purple. After rinsing the slide off with a gentle pressure of water, addition of Iodine on

To prepare a wet mount slide you begin with the substance at hand. The specimens studied in the laboratory using this type of slide were a hay infusion, a yeast suspension, and the mold specimen. For the hay infusion you begin with placing two drops of the suspension in the center of a clean microscope slide using a transfer pipet. The specimen must be immediately covered with a cover glass completing the wet mount slide. The yeast suspension is transferred from the tube to the slide using a flame sterilized inoculating loop. Immediately cover the specimen with a cover glass. The stained yeast suspension is prepared the same way except that the suspension is mixed with a drop of lactophenol cotton blue placed on the slide prior to transferring the yeast. The mold must be cut from the petri plate and placed on top of the drop of lactophenol cotton blue already placed on the microscope slide. After it is covered it may be studied under the microscope.