I believe OD correlates with mass concentration, not with numbers of cells.
Of course, if the cell size does not change as a function of growth
conditions, the correlation works for both. If you truly want cell number,
you need to go to light scattering measurements, not OD.
The correlation between mass concentration and OD needs to be established
for a particular organism, but for rough purposes literature values can be
used. Also, for measuring growth rate, you don't need a mass Vs. OD
correlation--OD by itself is good enough.
Frank Bartels wrote in message <35CA2E62.C77 at gbf.de>...
>Franco Pagotto wrote:
>>>> Hi all,
>>>> Is anyone aware of an equation which takes into account an OD reading
>> and gives or estimates the CFU's/ml of a bacterial growth?
>>The relation between cfu's and OD depends not only on the physiological
>state of the culture. In addition the type of microorganism has to be
>taken into account (e.g. the size of E. coli is different from
>Bacillus). The best way is to count the cells to have the relation
>between OD and cell number/ml. This should be constant. If every cell
>forms a colony is a different question.