1. How many bacteria are in 10ml of a broth, which is diluted 10 7 fold gives an
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Question
1. How many bacteria are in 10ml of a broth, which is diluted 107 fold gives an average of 40 CFUs/ml?
2. You need 10ml of a suspension containing 105 cells/ml. You have cells at a density of 2 x 106 cells/ml. What volume of cells and what volume of diluent would you use to prepare the desired suspension?
3. A commercial antibody has a concentration of 1 mg/ml. The directions say it should be diluted 1:10,000 for use in ELISA reactions. You are doing an ELISA test and will need 100ml of the solution. Describe how you would dilute the antibody. What will be the final concentration of antibody in your working solution?
Explanation / Answer
1. 40 CFUs/ml diluted 10^7 fold would be 4.0x10^8 CFUS/ml undiluted. Because we have 10ml of broth, then we would have 4.0x10^9 CFUs total.
2. C1V1=C2V2. We know C2V2 as (10^5 cells/ml)(10ml)=10^6, and we know C1 as 2x10^6 cells/ml. So substituting would give (2x10^6)V1=10^6. Thus V1=0.5ml or in other words, we use 0.5ml of the initial cell suspension and 9.5ml of the diluent.
3. 100ml/10,000=0.01ml. So, use 0.01ml or 10ul of the antibody into 100ml diluent (technically 99.99ml, but measuring out that accurately in a true lab setting that would be really dumb.) Your final concentration would be 1/10,000 of what you started with, so 0.0001mg/ml or 100ng/ml.
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