Question

What dilution of Staphylococcus is required if the initial concentration of the broth culture is 5.8*10^8 cells/ml and your goal is to have a spread plate with 98 colonies when 0.1ml is plated?

Answer 1

It can be calculate with the help of formula:

`\frac{\text{Number of CFU}}{\text{Volume plated (ml) x total dilution used}} = \text{Number of CFU per mL}`

where, number of CFU is given as 98,

Volume plated = 0.1mL

Number of CFU per mL =
`5.8\text{ x }10^(8)\text{ cells per mL}`

Hence,
`\frac{98}{0.1 \text{ x total dilution used}} = 5.8 \text{ x } 10^8`

⇒total dilution used =
`\frac{98}{0.1 \text{ x }5.8\text{ x } 10^(8)}`

⇒total dilution used =
`(98)/(58)` x
`10^(-6)`

⇒total dilution used =
`1.69\text{ x }10^(-6)`