bacterial growth

J. McGrath !!jmcg at frontiernet.net
Wed Aug 20 20:27:32 EST 1997


rick schuman wrote:

> Does anyone have a method (or reference) for preparing bacterial
> growth
> curves?  We need a procedure for accurately determining the number of
> organisms in a suspension before use.
>
> Please reply to r1623 at erols.com.
>
> Thanks in advance,
>
> Rick Schuman

rick schuman wrote:

> Does anyone have a method (or reference) for preparing bacterial
> growth
> curves?  We need a procedure for accurately determining the number of
> organisms in a suspension before use.
>
> Please reply to r1623 at erols.com.
>
> Thanks in advance,
>
> Rick Schuman

   You should be able to derive your own curves empirically using
visible light spectrophotometry.  This can be accomplished by growing
cultures of each organism of interest in nutrient broth, then making
several dilutions in isotonic buffer (and plate for quantitation).  Take
EACH dilution and place in spectrophotometer (not sure of wavelength but
if curve is linear and repeatable you should be able to use it).  Plot
Absorbance vs. CFU/ml for each dilution tube.  Now in the future your
cultures that are grown under similar conditions as the curve organisms
will have a absorbance and concentration relationship.  If you feel like
getting fancy a linear regression may be used to convert the curve to a
mathematical formula that will allow rapid conversion from absorbance to
CFU/ml.  I would revalidate the curve at least yearly, when strain of
test organism changes or when changes to growth parameters occur.  Not
sure of exact references I performed similar analyses long ago (10
years) but the concept here is correct.  Chemists use a similar
relationship of concentration vs absorbance which I fondly remember as
Beer's Law (my spelling).  Hope this helps.  Try a literature search on
medline or others using both "organism" "quantitation" and
"spectrophotometry".  Some real references should pop up.  Seeeeee
yaaaaaa.

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