Question

When answering the following questions, assume all dilutions are in even power of 10, unless told otherwise, and that 0.1 mL (100uL) or 1.0 mL (1,000 uL) volumes were plated. Also, cell density and cell concentration are used interchangeably, as are CFU and colonies, depending on how the term is being used.

Please answer the question using the formula V₁D₁ = V₂D₂.....Please show details

1. Suppose your professor handed you a test tube with 2.0 mL of an E.coli broth culture in it and told you to make a 10^-1 dilution of the entire culture. Explain how you would do this. Show your calculations.

Answer 1

Consider you have 2.0 mL of an E.coli broth culture whose concentration is 10X now you want 1 ml of 1X concentrated E.coli broth culture. To get 1X you should do 10^-1 dilution (10 times dilution) of original 2 ml of 10X stock.

Stock E.coli broth culture concentration                                =10X

Required E.coli broth culture concentration                           =1X

Required final volume = 1 ml

V1D1   (Concentrated)   =     V2D2 (Diluted)

10X     *          xul       =          1X*1 ml

xul      = 1X* 1 ml /10X

=          0.1 ml

Take 0.1 ml of stock and add 0.9 ml of media you will get 1 ml of 1X working stock. Here the original stock is diluted 10 times/ 10^-1 dilution  

For 1ml            0.1 ml of stock and add 0.9 ml of media                    10^-1 dilution/10 times dilution

10 ml               1 ml of stock and add 9 ml of media                          10^-1 dilution/10 times dilution    

100ml              10 ml of stock and add 90 ml of media                      10^-1 dilution/10 times dilution