filter sterilization of antibiotic stock solutions - Is it necessary? (May/10/2010 )

Hello,
When preparing antibiotic atocks like ampicillin, kanamycin etc, is it necessary to filter them? What will happen If it is used without sterilization? It is an antibiotic, so how will contamination occur in it?

Think about the mode of action of antibiotics: some kill gram positive, some gram negative... so why would you filter?

lotus on May 10 2010, 05:30 PM said:

I end up making quite a few strains of E. coli that carry plasmids with antibiotic resistance to kan, amp, chlor, tet, etc. Those can contaminate just as well as any other organism.

Of course, I usually don't filter sterilize antibiotics myself, and have never had much of a problem with contamination. I would imagine our stock solutions of antibiotics (in the mg/ml range) are a little harder to overcome than the ug/ml concentrations we use for culture.

During my PhD we had a saying "if it can grow in concentrated Amp/Kan at -20 then it deserves to live"

We didn't filter our antibiotics.

You should always think of good lab practice! Saving time in the lab by cutting short the preparation time of media usually does not pay, but will go back on you as you will have to repeat the exp.

Even if contaminations caused by the added antibiotic stock solution are rare, you should always keep in mind that the minimal effort it takes to filter sterilise can prevent you from strange results and repeating your experiment.