Hi. You correctly did it, but if you are meticulous :) and want to use intact bacterial medium for each OD measurement you can make 60ml medium for each bacterial sample/treatment and divide it into 6 bottles (10ml in each bottle) and for each measurement at each 12 hrs use one of them.

Assuming that you are shaking the bottle so that the culture is well mixed, you can just take the OD of a representative sample, such as your 2ml. But don't forget that if you are at high cell densities an OD reading is not very accurate when you go above 1.0

I agree with and recommend what Mohsen and Micheal said.

1. Make sure you shake the bottle properly (before you take the sample for measuring OD) so that the culture is as homogenously suspended as possible.

2. If your total culture is 10 ml, removing 2 ml each time is going to rapidly deplete the volume- not only limiting how many measurements you can take, but also affecting the growth over time. So, have separate bottles for each measurement.

With these precautions, you can use the OD of the 2 ml as representative of the 10 ml.

Finally, if the OD increases to the limits of the instrument (often ~1.0), then you can dilute the sample before measuring, and then extrapolate the measurement to get the actual OD.

Good luck!

Hi Armstrong,

The OD600 reading from different time points will eventually reach a 'plateau' (see attached example). In this attached example, after 5 hours the OD600 reading reaches plateau (OD600 readings are all similar after that point). 

You can use the OD600 reading from the 2-mL sample to represent the 10-mL culture when the bacterial growth is in the 'log phase' (see attached pic). But, as Michael suggested, higher readings even before the plateau may be less accurate.

I also attached this paper for your reference. Fig 5 and Fig 6 in the paper explain 'bacterial growth rate' experiment. Hopefully it helpful.

Best,

thanks very much for your contributions