Determining Unknown in Microbiology Lab

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.

For many years the identification of microorganisms has been important in the world of medicine. It is essential or correct disease diagnosis in patients and for proper treatment. Knowing the correct identity and characteristics of microorganism is crucial when disease outbreaks occur in populations, also knowing how humans can benefit from microorganisms is important; many can be used in making certain foods or antibiotics.

Using the information found in the Gram Negative Enteric Baccilli and Gram Positive Cocci Reference books,

I began by running the starch test, which tests for the presence of starch hydrolyzing enzymes. After doing a one-line inoculation of the organism, the plate had to be incubated. Once I received an appropriate amount of growth I added the reagent iodine. The iodine turned the plate purple, formed no clear zone, and lifted the organism off of the plate, which revealed that the starch was not degraded and the enzyme was not present. The organism being lifted off the plate is unique to the bacteria Corynebacterium xerosis indicating that it was my gram positive rod. For reassurance, I ran the Phenol Red Glucose test, which tests if the organism contains various enzymes that determine if the bacteria can ferment glucose. After incubation, the broth turned orange, but this did not provide a clear positive or negative result so I ran the Nitrate Broth Reduction test. The Nitrate Broth Reduction test detects if the organism utilizes nitrate. After incubation for forty-eight hours I added Nitrate A and Nitrate B indicators. However, there was no color change indicating that the test was inconclusive. Since the test was inconclusive, I proceeded to the following step, which included adding a small amount of zinc to the broth, and this turned the broth a red color. The red color indicated that

Often scientists work with bacteria that do not come in a labeled test tube— for example, bacterial samples taken from infected human tissue or from the soil—and the scientist must then identify the unknown microorganism in order to understand what behavior to expect from the organism, for example, a certain type of infection or antibiotic resistance. However, because of the relatively few forms of bacteria compared to animals and because of the lack of bacterial fossil records due to their asexually reproductive nature, the taxonomy used to classify animals cannot be applied to bacteria (Brown 275). In order to classify unknown bacteria, a variety of physiological and metabolic tests are available to narrow a sample down from the fathomless number of possibilities into a more manageable range. Once these tests have been performed, the researcher can consult Bergey’s Manual of Determinative Bacteriology, a systematically arranged and continually updated collection of all known bacteria based on their structure, metabolism, and other attributes.

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.

|EMB Agar | |Distinguishes bacteria that ferment |Dark blue colonies with|E. coli and P. |

For the Urease test, I incoluated my Urea test tube with my unkown bacteria from a TSA plate using and inoculating loop. The Urea tube was then incubated at 37 degrees Celsius for 8 days to observe for a color change. The Urea tests for the ability of a bacteria grown in urea broth produces urease. This medium contains the pH indicator phenol red. If urease is produced the pH of the media will raise thus causing the phenol red to change from yellow to a pink color.

The identification of unknown organisms carries important ramifications that can be applied to many real world scenarios. In keeping with quality assurance beverages, food, cosmetics, and other products are frequently inspected for contaminants resulting from a presence of pathogenic bacteria. In medicine, a physician’s diagnosis and consequent treatment is largely determined from samples collected from infection sites that have been analyzed using microbial tests.

This lab and its procedures are all about finding out the unknown identification of a given bacteria. The lab consists of specific techniques, tests, chemicals, and vocabulary that are necessary for the finding of the bacterial identity. A bacterium is randomly assigned and it is a group effort to find the bacteria name through many of its specialties and characteristics. An example of classifying it would be to determine whether the bacteria is catalase negative or positive, or if the species is gram negative or positive. This lab is of huge significance because of its medical microbiology connections. Scientists Gurtler and Stanisich explained the connections more eloquently. They stated, in their medical article, that, “Medical microbiology

In category IV, agar plates were used containing differential and selective aspects to determine the unknown bacterium. The first media test was the EMB. EMB separates fecal coliforms that are produced through carbohydrates that are fermentable, such as sucrose and lactose. The different fecal coliforms represent the differential factor of this test, while the selective factor selects against gram positive organisms. Lactose fermenters appear purple, pink, blue, and black colonies, while non-lactose fermenters appear clear to light orange. This occurs because Eosin Y and methylene indicators react at low pH forming the purple precipitate. On the other hand, vigorous fermenters appear metallic green indicate either coliform production or lactose

The unknown bacteria #9 produced negative results for H2S in the SIM test tube. The medium stayed semi-clear and did not turn black.

Another purpose of this experiment is to stress the importance of knowing the identity of a microorganism. Knowing the species of microorganism present in a sample provides a

Correct identification of a microorganism allows for proper investigation of a particular species, and prevention or treatment of a disease if necessary. During lab, students were instructed to choose a test tube inoculated with an unknown organism and then prompted to initiate a series of appropriate lab tests to correctly identify the organism.