Essay about Micro Lab Project

757 Words May 5th, 2015 4 Pages
Quantitative & Semi-quantitative Viable Plate Counts
Molly Wright, Jenny Cano, Rosa Ramirez
BIOL 2420 Lab M/W
Professor Rotibi

ABSTRACT: Accurate evaluation of bacterial colonization as a predictive index for alfalfa sprouts has relied on a quantitative culture technique that provides exact colony counts per gram of tissue by culture of five serial dilutions of the alfalfa water. In this study 1 package of alfalfa sprouts were cultured by a semi-quantitative technique that enumerated the number of gram-negative enteric organism in 1 ml of alfalfa water. Exact colony counts from the experiment were available only from cultures 10-2 and 10-3 CFUs. Other colony counts were reported as less than 10-3 or greater than
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Preparing serial dilutions of the alfalfa water will ensure an accurate count. The plates are incubated until you see visible colonies, usually 18-24 hours. The colonies you see growing on the plate are considered to have started from one viable bacterial unit but because bacteria are usually not found as individuals, the colony you see may have started from a single cell or a group of cells. The results are reported as colony forming units (CFU’s).
-1 pkg. of alfalfa sprouts purchased at a local grocery store or farmer’s market, submerged in 100 ml of sterile, distilled water. (Any other food or beverage item may be substituted for alfalfa sprouts)
-Graduated pipettes (sterile)
-5 tubes containing 9 ml of sterile water
-5 MacConkey Agar plates
-Glass hockey stick
-Jar of alcohol
-Bunsen burner
-Flint striker
-Microscope slide & Glass coverslips
1. Make a wet mount (Ex 12) of a small sample of the alfalfa water. Examine at 1000X total magnification using high contrast. This will illustrate how many organisms, both motile and non-motile, are present in the sample.
2. Make 10-old dilutions according to the diagram (Fig. 16.2).
3. Use a sterile pipette to transfer 0.1 ml of each dilution on to a MacConkey agar plate.
4. Wet a glass hockey stick in alcohol and pass through a flame to ignite. Wait approximately 30 seconds for the glass to cool.
5. Spread the 0.1 ml sample out with the glass hockey stick
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