You would like to determine the cell density in a freshly prepared culture of E. coli. The culture was prepared as follows: Tryptone broth (99.5 ml) was inoculated with 0.5 ml of an older E. coli culture. A serial dilution of the freshly prepared culture was performed as follows: A volume of 0.1 ml is withdrawn from the culture and diluted into 9.9 ml of saline. The diluted sample is vortexed and 0.2 ml are withdrawn and transferred into 9.8 ml of saline. The second diluted sample is vortexed to ensure proper mixing. A volume of 100 µl is withdrawn and spread onto an agar plate. Following overnight incubation, 280 colonies are counted. How many total viable cells are present in the entire 100 ml of the freshly prepared culture? State only the answer (a number) with the correct units.
Added by Sara N.
Step 1
The dilution factor for the second dilution is 1/5000. Therefore, the total dilution factor is 1/100 * 1/5000 = 1/500000. Show more…
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You would like to determine the cell density in a freshly prepared culture of E. coli. The culture was prepared as follows: Tryptone broth (95.5 ml) was inoculated with 0.5 ml of an older E. coli culture. A serial dilution of the freshly prepared culture was performed as follows: A volume of 0.1 ml is withdrawn from the culture and diluted into 9.9 ml of saline. The diluted sample is vortexed and 0.2 ml are withdrawn and transferred into 9.8 ml of saline. The second diluted sample is vortexed to ensure proper mixing. A volume of 100 µl is withdrawn and spread onto an agar plate. Following overnight incubation, 280 colonies are counted. What is the concentration (CFU/ml) of viable cells in the freshly prepared culture? State the answer with the correct units.
Farhan A.
You would like to determine the cell density in a freshly prepared culture of E. coli. The culture was prepared as follows: Tryptone broth (95.5 ml) was inoculated with 0.5 ml of an older E. coli culture. A serial dilution of the freshly prepared culture was performed as follows: A volume of 0.1 ml is withdrawn from the culture and diluted into 9.9 ml of saline. The diluted sample is vortexed and 0.2 ml are withdrawn and transferred into 9.8 ml of saline. The second diluted sample is vortexed to ensure proper mixing. A volume of 100 µl is withdrawn and spread onto an agar plate. Following overnight incubation, 280 colonies are counted. What was the concentration of cells (in CFU/ml) in the older E. coli culture from which the 0.5 ml were withdrawn and used for inoculating 100 ml of growth medium? State only the answer (a number) with the correct units. Note: Similar questions are posted, however in the last 3 sentences its asking for something else.
Andrew M.
We made a simple estimate of the mass of an $E$. coll cell by assuming that such cells have the same density of water. However, a more reasonable estimate is that the density of the macromolecules of the cell is 1.3 times that of water $(\mathrm{BNID} 101502,104272) .$ As a result, the estimate of the mass of an $E$ coli cell is off by a bit. Using that two-thirds of the mass is water and that the remaining one-third is macromolecular, compute the percentage error made by treating the macromolecular density as the same as that of water.
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