bacterial dilutions for spectrophotometer measurements

[Silvia_84]

Hi all,

 

I am encountering difficulties trying to figure out some calculations I have to do in order to diluite (or concentrate) my 2 bacterial solutions for a MIC test. I should adjust the density of my overnight cultures with water to equal that of the 0.5 McFarland Standard, which is roughly equivalent to OD600 0.08-0.1 (10⁷-10⁸ cfu/ml). I diluted my original overnight cultures like this: 1900 ul of water and 100 ul of overnight culture (total: 2 ml) and I take 1 ml of this solution for the measurements at the spectrophotometer. One culture has an OD of 1.10, so I have to diluite it and the other 0.06 so I should concentrate it. My question is : how do I diluite the first ? and viceversa..for the second..how do I concentrate it? which calculation should I do?

 

Any suggestion would be really appreciated.

 

Thank you in advance.

 

Silvia