Determining Unknown in Microbiology Lab Essay

1142 Words Jan 17th, 2012 5 Pages
Determining an Unknown Through
Deferential Stains and Biochemical Tests

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 have been learned so far in the microbiology laboratory class for the identification of unknown bacteria. The identification process can be completed with a series of deferential stains and biochemical tests. Creating a dichotomous key helps to limit the amount of biochemical tests done on an unknown organism and by observation
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If the cell is gram positive, the ethanol acts as a protein dehydrating agent causing the pores to close up and lock in the primary stain so the cell is purple. Viewing these stained samples under a high power microscope lens enables the shape and gram stain to be determined. Streaking the gram negative bacteria on an EMB plate will help finalize the conclusion of the bacteria. Biochemical tests make use of enzymatic activities to differentiate among bacteria by products of biochemical reactions causing changes to the medium that have inoculated the organism with. This means that they identify whether specific reactions are occurring in the cell by testing for the presence or absence of enzymes or products. Tests that show the presence of these enzymes or products are considered positive tests and the tests that show a lack of these enzymes or products are negative. The lactose fermentation test contains one of the following carbohydrates (sucrose, maltose, and lactose) and a pH indicator to detect acid formation. The broth tubes containing phenol red start as bright red by inoculating the medium with the gram positive colony it should indicate whether the bacteria is positive or negative. If fermentation is occurring and acid is being produced, the broth will change to a yellow color. If no color change occurs, the result is a negative test. These broth tubes also contain a durham tube. This durham tube detects the presence of gas production from the

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