Typical Klett users utilize an erlenmeyer flask with a side arm, which is nice
because one does not have to open the seal on the flask. Klettsters frequently
(as a matter of convenience) does not do a dilution of the culture in such a case
to see the true absorbance/transmittance/klett. Errors as culture reaches
stationary phase may be as high as 50%. Spectrometer users typically take an
aliquot from the culture flask and then may or may not dilute dense samples to
avoid deviance from linearity.
The growth curve itself: we are interested in the period of lag, the rate of
exponential growth or the slope of the curve, and the time of entry into
stationary phases (and perhaps slight density increases in early stationary phase
and density declines in deep stationary phases).
Does the practice of not diluting dense cultures significantly affect
your determination of entry into stationary phase, the exponential rate
of growth?
What is the purpose of making a dry weight vs. OD curve, besides busy work?
(revealing that he does not make such curves, unless requested by the PI).
We could substitute CFUs or bacterial dried weight for the
concentration in A=ebc. Which is more useful? Most folks just give an
absorbance versus time curve.
-Andrew Heath
Research Associate
University of Michigan
Infectious Diseases
R. I. Mateles <rmateles at candida.com> wrote:
: Klett's are old, but they are (were) quite useful. They do not function at
: a narrow wavelength, but they give perfectly valid curves of reading vs. dry
: weight after you calibrate them for the particular suspension you are
: measuring. If you use a spectrophotometer, you still need to prepare a dry
: weight vs. OD curve for each type of suspension, it's all more "modern", but
: the results are about as good or bad as with a Klett! In both cases you get
: a mixture of scattering and absorption. and in both cases you have a more or
: less linear part of the curve and a part which is non-linear (at higher
: densities).
: Rich Mateles
