After colony 25012/13/2023 Step 4: Indicate if you want the chart as a new sheet or as an object in present chart. Step 3: Add appropriate title, X and Y units. If data graphed are not correct, click series and enter the correct X and Y values. Step 2: Data range should include your selected data cells ($A$1:$B$5). With the mouse choose ( click) the icon at the top of your screen called “Chart Wizard.”Į. Your data cells (and only your data cells) should be highlighted.ĭ. With the mouse, start in cell A1 and drag the mouse to B5. At this point you would have data in cells A1 to A5 and B1 to B5 (if using the data from Figure 2). For example, enter the exponent 5.1 x 10 7 by typing 5.1 E7 the display will show 5.1E +07.Ĭ. When entering average CFUs/ml that include exponents, they are entered as X EY. Enter the time points in descending order in column A and corresponding colony counts (or average CFU/ml) in column B. Directions are for Microsoft Office 2000.ī. To graph these data, start the spreadsheet software package Microsoft Excel. time, using the following instructions:Ī. These numbers would then be entered into an Microsoft Excel spreadsheet and the log of the average cell count (CFU/ml) graphed vs. The results of a growth curve of Escherichia coli grown at 37 oC on nutrient broth (one ml plated).ĪAmounts that are significant are in bold type. How many CFUs were in the original sample?Įxample 2: After plating 0.2 ml of a 10 -5 dilution, 183 colonies grew. Then 4 serial 10-fold dilutions are made. transferred + diluent volume Total VolumeĮxample #1: 1 ml of culture was transferred to 99 ml of diluent.Īnswer: Dilution = 1 ml = 1 ml = 1 or 10 -2Įxample #2: 1 ml of a bacterial culture is transferred to 9.0 ml of diluent. 1.5 x 10 8 (Remember: 1 x 10 a = 10 a).ĭilution = _Volume transferred_ = Volume transferred Answers should be written with two significant figures in proper scientific notation, i.e. Because dilutions are large when counting bacteria, exponents are used. The most common dilutions are 1/10 and 1/100, but any dilution can be made. In order to make the calculation of the number of cells/ml in the original samples less formidable, dilutions are designed to be easy to handle mathematically. If more than one plate is countable, average the counts together. In this way you will have at least 1-2 plates within the countable range (25-250) to use in your calculations. When the approximate number of bacteria is unknown, plate a wide range of dilutions. Plates with less than 25 colonies do not have a statistically significant number of colonies. Counts above 250 are considered Too Numerous To Count (TNTC) because it is impossible to tell whether colonies are separated. Ideally only plates with 25-250 colonies are used. For this reason results are reported as colony forming units (CFU)/ml of bacterial culture. Not all bacterial cells produce colonies, as some bacteria tend to clump or aggregate, and some are nonviable. It is imperative that you utilize your best aseptic technique. If you perform a viable count to determine the number of bacteria in a culture, plate aliquots of the dilutions onto agar with sterile pipettes, spread with glass hockey sticks, incubate at 37☌ and count the number of colonies. Tips for handling specific types of data:
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