Micro Lab Unknown Organism Report 3m1i59

Microbiology 2325L Identification of Unknown Bacteria Unknown Code: C14 Abstract: The unknown organism given was in a petri dish labeled C14. Experiments performed on the organism in the Microbiology laboratory along with research regarding the results, led to the identification of the organism. Following identification, research began, which illustrated diseases caused by the organism and treatments to fight those diseases. Background: Table 1: Testing results for Serratia marcescens Test

Gram Stain

Urease Test

Purpose of test

Reagents/Media

Observations

Results

The purpose of the Gram stain test was to determine the Gram stain reaction of the bacterium.

Crystal violet, Gram’s Iodine, 95% ethanol, and Safranin were used in the Gram stain test.

The organism appeared bacillusshaped, stained purple in color and could either be arranged in chains or clusters.

Gram negative

The purpose of the urease test is to determine if the organism is positive for the urease enzyme

Nutrient broth deeps, pH indicator, phenol red.

The broth was yellow in color.

Negative for the urease enzyme

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and therefore belongs to the Genus Proteus. After receiving the unknown organism in plate C14, careful observations were made regarding the appearance of the bacterium on the plate. The bacterium initially appeared to be raised and light pink in color. After observing the organism on the same plate a week later, it still appeared raised, but the color changed from light pink to a darker brick color. The first experiment performed to determine the identity of the organism was a Gram stain. The Gram stain is used to differentiate between cells by differences in the cell wall structure. Gram positive organisms have a thicker peptidoglycan layer in their cell wall than Gram negative organisms, which drastically helps in differentiating between the two. During this procedure a sterile inoculating loop was used to prepare a bacterial smear on a slide, which was then heat fixed. After heat fixing, the primary stain, Crystal Violet was used to flood the smear, coloring all cells on the slide purple. A mordant, Gram’s Iodine, was then used to bind to the Crystal Violet and the cell wall. Next, a decolorizer, 95% Ethanol was used to selectively remove dye from cells based on certain characteristics of the cell wall. Gram positive organisms remain the color of the primary stain due to their thick peptidoglycan layer, while Gram negative organisms are colorless after the 95% ethanol is used. The final reagent in the Gram stain experiment was the counterstain, Safranin, which binds to colorless Gram negative organisms causing them to appear pink in color. Unknown organism, C 14 appeared pink in color following the Gram stain experiment, proving it is a Gram negative bacterium. This finding helped to eliminate the Gram positive organisms on the list of possible unknown organisms.

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While looking at the organism more closely, under a microscope, it was noticed that the appearance of the unknown organism was bacillus and the arrangement of the bacterium was either in chains or clusters, but it was hard to tell. There were no visible spores. A second experiment was performed to assist in the identification of the unknown organism. This test was the urease test, which was used to test the organism for the urease enzyme, which hydrolyzes urea, a nitrogenous compound found in urine. Organisms from the Genus, Proteus, are positive for the urease enzyme. Ammonia and hydroxyl ions resulting from the breakdown of urea cause an increase in the pH of organisms positive for the urease enzyme. A pH indicator, phenol red, changes from yellow to red, due to the increase in pH in organisms positive for the urease enzyme. After performing the urease test on unknown organism C 14, the media remained yellow in color, disproving the production of the urease enzyme. The results of this test were helpful in eliminating Proteus mirabilis from the list of possible unknown organisms. Unknown Organism: The unknown organism labeled C 14 is Serratia marcescens. Serratia marcescens is a Gram negative, bacillus organism with short rods, which presents itself as pink or red at room temperature. S. marcescens belongs in the Enterobacteriaceae family and occurs naturally in soil, water, and in the intestines. It is a human pathogen and is involved in nosocomial infections, including wound infections and urinary tract infections. Researching this bacterium was a little difficult, because most of the articles were very similar or not from reputable sources.

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S. marcescens

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