Tuesday, September 13, 2011

Preparation of Culture Media?

1.From what source do bacteria obtain their mineral elements like, Ca, Mg, Fe, etc. in nutrient broth? (agar is used as the medium)

2.How can one remedy the effect of pH change due to sterilization?

3. What is the difference between the sterilized and unsterilized media?

4. Is there any effect of the pH to the keeping of unsterilized media?Preparation of Culture Media?
1.

There are two types of media.

';Synthetic'; and ';Complete';



If synthetic

Would have to add all the components using pure chemical stocks.



If complete.

Can use yeast extract which contains alot of compounds, minerals, vitamins, organics etc.

A hydrolysate (bacto-peptone), often from milk.

Also a good source of nutrients, amino acids



2.

The pH of the media should be adjusted to an optimal or near-optimal pH for the particular bacteria species.

Bacteria such as E. coli grow best at a pH 7.2+/-0.4

Lactobaccillus is on the acidic side.



Yes, the pH of media will change typically by 0.3.

If it is important to have an exact critical final pH.

You can make an adjustment before autoclaving.

Also don't autoclave anything longer than needed.

Just long enough to kill any microbes and melt the agar.

Can get undesirable chemical reactions.

Esp. if it is acidic. Might hydrolyse sugars and the agar.



If liquid medium, alternative is to filter sterilize.



Sometimes pH buffers are added to the medium.

Can be autoclaved separately and added to flask containing the medium.



3.

Sterilized vs. un- or nonsterilized medium.

Sterilized will have less contaminating wild bacteria, yeasts and mold growing on it.



4.

Non-sterilized medium will eventually show obvious signs of mold etc. growing in it.

If stored in the refrigerator, the cooler temperature will delay the growth of contaminants.

Some contaminates grow better or suppressed at certain pH.
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