Practical Molecular Biology - home page.
 > Calculations > Bacteria growth.

Help for bacteria growth.


Suppose, that it is necessary to obtain bacterial culture with the OD=0.500. If the first measurement was at 9:20 (OD1=0.050), the second - at 14:45 (OD2=0.270) then if you write these data in a form as shown below and push on "Calculate", you will obtain that bacteria reach 0.5 density at 16:43 (or, after 1h58min since the second measurement).

Suppose, that the culture is slow growing, and the first (9:20) measurement was yesterday. In this case it is necessary to add "1" (or "-1", does not matter) in the upper field. Result will be: 1d = next day, at 1:29; or 10h44min since the second measurement.


The first measurement was days before at:
   h* min* => OD1 = *
The second measurement was today at:
   h* min* => OD2 = *

Bacterial culture reach the indicated density

after days at:
          =>ODf = *  

   Or, after   since the second measurement.

 

Return to the "0" in the upper field and recalculate again. Let's estimate the precision. If the precision of optical density ±0.001 and time - ±7 min it will be ±4min.


Evaluation the precision of the prognosis.

only after evaluation of the growth time
  Precision of the spectrophotometer: ±OD
  Precision of the time measurement: ±t[min]
  Precision of the evaluation: ±t[min]
 
± *
± *
± 

 
For bacteria in the logarithmic stage of growth:
OD1 = A * exp{k(t1 - t0)}
OD2 = A * exp{k(t2 - t0)}
ODf = A * exp{k(tf - t0)}
Solution of these equations:

tf = t2 + (t2 - t1) * ln(ODf/OD2) / ln(OD2/OD1)

For the precision:

± tf = (tf - t2) * {(d_t)2/(t2 - t1)2 + (d_d)2(1 / OD12 + 2 / OD22)}1/2



"Practical Molecular Biology" http://molbiol.edu.ru;
e-mail: pmb@molbiol.edu.ru


Rambler's Top100