lmackey at isat.com (Larry Mackey) wrote:
>My 13 year old daughter wants to do an experiment looking for
>different types of bateria, etc.
>>If I remember correctly the medium used in the peitre dishes is agar.
>I am at a loss where to start looking for suppliers that might carry
>this or if there is a way of making up suitable medium from commercial
>(household) materials.
>>any pointers would be greatly appreciated.
>
Dear friend,
I teach microbiology in Thailand.
We often use the ready made soup stock (you can get
it from the supermarket) for medium. Agar is
also available in the supermarket - otherwise you
could use jello - it will work.
One thing that you must have is a pressure cooker!
Let me explain.....
Bacteria and most other microorganisms will eat like
us. They need proteins, sugars, fat etc. To grow them
you can use the beef extract, the soup stock, or you
could boil up some chicken and use the chicken soup.
In fact, most microbiological media that are use in
the laboratory are made this way (by the big company
like DIFCO and they ship to us in the powder form).
These liquid medium are call "broth". When the
bacteria grow in it, the liquid becomes turbid.
Turbidity is the sign of bacterial growth.
Sometimes, we want to grow the bacteria on a
solid surface - to see the characteristics of
the bacteria. We put AGAR into the soup stock.
Agar has no nutritional value, it is just a
solidifying agent. We usually use 15 grams of
agar per liter of medium. You have to boil the
agar to melt and mix it. In the old days, we
also use gelatin for this purpose.
My guess is, if you put some sugar and chicken stock
into Jello - it will also work!
Now comes a difficult point, there are bacteria
everywhere!!!! I mean everywhere! On your hands,
on the table, in the air, in the pots and pans...etc
When you make medium (chicken soup or chicken agar)
for this experiment. You must kill all the
bacteria, otherwise your medium will not keep very
long before the experiment. To kill all the bugs,
you need a pressure cooker. Simple boiling will not
kill all the bacteria. We use this pressure cooker
all the time in our laboratory. The scientific name
is the AUTOCLAVE.
However, if your kid's experiment is just to cultivate
any bacteria, you may not need the pressure cooker,
because you will be welcoming all the bacteria anyway.
Hope my 2 cents helps
Umnarj.
