serial Dilutions

Tim Chance tim.chance at tesco.net
Mon Mar 26 17:18:43 EST 2001


Serial dilutions can really be any volume you want, as long as the
proportions are correct. For a logarithmic dilution series
(1/10,1/100,1/1000 etc) you want a series of tubes or microtitre wells the
first of which contains one volume of your solution or supension which is
to be diluted, the remaining tubes contain 9 tenths of this volume. Take
one tenth out of the first tube and transfer to tube 2, mix well and
transfer one tenth from tube 2 to tube 3 and so on discarding 0.1ml from
the final tube. If tube 1 contains 1ml then the remaining tubes will each
contain 0.9ml and you will transfer 0.1ml. When you have finished you
should have 0.9ml in every tube. Tube 1 will contain the original
concentration of analyte, tube 2 will contain 1 tenth the concentration,
tube 3 1 hundredth and so on. The actual volume you are using in the
experiments you are doing will probably have been decided by your lecturers
but in practice will depend upon what apparatus you are using (test tubes
or microtitre wells for instance), the cost of the reagents (if you are
testing an expensive antibiotic it's best to make small volumes) and what
has been found to work best previously. A logarithmic series of dilutions
will quickly dilute a substance to infinity and the steps between each
dilution become very large so in many cases a doubling dilution is used
instead to give 1/2, 1/4, 1/8 etc. Look up methods of MIC testing, broth
dilution and broth microdilution for more details.
Hope this helps.

Ndnassu <ndnassu at aol.com> wrote in article
<20010325174343.08674.00000834 at ng-me1.aol.com>...
> Hi,
> 
> I am some what of a novel microbiologist (1st year ) who is having
difficulty
> with serial dilutions.  In particular, how does one know to use 9.9ml or
9.0ml
> (diluent) or the .1ml or 1ml (inoculum) to reach desired dilution.  I am
aware
> that the total should = 10ml, but I am having difficulty manipulating the
> amounts for the desired dilutions.  I know, it is most likely very
simple, but
> I am just not seeing it
> 
> Thanks in advance,
> Yo
> 




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