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Agrobacterium on ampi or carbenicillin - (Jan/05/2007 )

Hi guys,

We're having a stange thing going on in the lab. We're trying to grow Agrobacterium rhizogenes K599 which should be ampicillin suseptible. It doesn't grow on carbenicillin 50ug/ml (which should be a more stable equivalent of ampicillin as far as I know) but does grow on ampicillin )either 50ug/ml or 100ug/ml). To check our ampicillin media and stock solution we used E.coli DH5a as a quick control: no growth on either ampicillin (50ug/ml and 100ug/ml) or carbeniccillin (50ug/ml). so to me the mpicillin stock and media are ok.

Can someone explain why Agro is growing on ampi and not on carb?

Thanks a lot!

-Dr T.-

I'd suggest doing an antibiotic sensitivity analysis for E. coli and Agrobacter with both your ampicillin stock and your carbenicillin stock. This is easy to do by infecting plain medium, adding it to a sterile 96 well plate, and then doing serial dilution of the antibiotic stock across the plate. If you start with 1 mg/ml antibiotic and do 2x serial dilutions, you'll hit about .25 ug/ml after 12 wells, and will get an excellent view of the antibiotic sensitivity of your organisms to the two antibiotics. I'd guess that they are substantially different, or that your antibiotic stocks are substantially different. This is an easy experiment, and should pin down the situation.