10 replies to this topic

[subha]

Hello all,
I did a stupid mistake, and realized it later. We usually store Ampicillin and Kanamycin antibiotic solutions (50mg/ml) at 20 degree C. But somehow after using those antibiotics , I left them at room temperature(25/26 degree C) for 2/3 days . After realizing the mistake I quickly put them back in -20 degreeC. Will they be fine , or I have to prepare new ones?

[lotus]

toss them and prepare new ones. They might still retain some antibiotic activity, but you can't tell how much.

[GeorgeWolff]

agree with lotus - for 2 reasons.  One, it's sloppy science and two they may be contaminaed.

[molgen]

I agree with lotus andGeorgeWolff - for one more reson: They're not that expensive that it pays to take the chance to go one working with them.

[bob1]

I wouldn't trust the amp, but the Kan is stable for 5 days at 37 deg C and for long term storage at 2-8 deg C, according to the product sheet.

[GeorgeWolff]

Wouldn't consider kanamycin or any antibiotic "stable" in context of a nonsterile solution.

[bob1]

OP says nothing about contaminated, just says that they left the antibiotics on the bench overnight.  I was assuming standard sterile practice.

[perneseblue]

Personally, unless this antibiotic is being used for titration purposes, I would still use the antibiotic.
Certainly there is some degradation. But does it matter in this situation? The amount of ampicilin used in a selection plate for cloning purposes varies from 100ug/ml to 25ug/ml. My lab uses 25ug/ml but I have seen labs  use 100ug/ml

So, if you assume degradation of the antibiotic I would use 50ug/ml or 100ug/ml which would give me more than enough antibiotic for selection.

I feel it is such a waste to dump a vial of antibiotic stock solution, when the finally concentration of the antibiotic isn't important.

[Paraboxa]

I think I'd still use the antibiotics. Note down in your lab book what happened and obviously you'll record which batch of antibiotic you use so that you can trace dodgy results.

Do you run a test plate when you make up your antibiotics? You could run a plate to test the efficiency of your experimental dose. (Not that I ever did a test plate on each antibiotic batch I made up. Does anyone else?).

[GeorgeWolff]

At minimum, make sure the solution  has not become contaminated.

[HomeBrew]

If contamination is a suspected issue, push the solution through a 0.22 um syringe top filter.

I personally would toss the antibiotic and make a fresh stock because most of the time, the antibiotic comes into play after I've performed many laborious steps leading up to selection, and I'd rather waste some antibiotic then all that labor.