Culturing antibiotic resistant bacteria on regular media?

[MC]

I have a very basic question as a beginning bio student: What would happen if you sub-cultured something like E. coli with a ampicillin resistant plasmid that's currently growing on amp LB onto plain LB?

My hypothesis based on my limited experience is that assuming no contamination, it will grow but so will E. coli lacking the amp resistance. But why? Do mutations occur in asexual reproduction for the sake of genetic diversity?

[Dennis Oleksyuk]

The ampicillin resistant bacteria will grow on a media without ampicillin. It will just express the resistance protein but it will not be used for anything.

Over time the bacteria will lose its resistance because of mutations introduced during DNA replication and evolutionary pressure to save energy otherwise spent on producing ampicillin digesting proteins. 

On Tue, Apr 4, 2017 at 12:12 PM MC <marky...@gmail.com> wrote:

I have a very basic question as a beginning bio student: What would happen if you sub-cultured something like E. coli with a ampicillin resistant plasmid that's currently growing on amp LB onto plain LB?

My hypothesis based on my limited experience is that assuming no contamination, it will grow but so will E. coli lacking the amp resistance. But why? Do mutations occur in asexual reproduction for the sake of genetic diversity?

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[Mega [Andreas Stuermer]]

Imagine there were no amplification errors and no radiation mutations. Then the world would still be settled with the first viable organism ;) 

With E coli you are definitely right. In theory there could be a bacterium that can only grow hen Amp is present, if all the other metabolic enzymes have mutated and only ampicillin could be used as energy source. Some bacteria can't be cultivated in a dish because they live in communities in nature. 

Stay curious ;) 

[Nathan McCorkle]

Unfortunately the original reference link is dead, but this says at
incubator temperatures (37 C) ampicillin only lasts 3 days:
http://www.openwetware.org/wiki/Ampicillin#Stability

Just something I came across recently that was interesting to think
about. I sub-cultured some cells and put them in the fridge the next
day for storage, thinking I could get a few weeks of fridge storage
that way, before having to re-culture.

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[Matt Champion]

In general with a single passage and only ~1 colony selected for sub-work the plasmid will almost always be present; depending on its copy number. However it will lose the AmpR phenotype but not due to mutation.  Without the selective pressure of the antibiotic, the bacteria will not maintain the plasmid as it is at a competitive disadvantage in laboratory conditions. Dennis's answer is mostly correct, but the loss of plasmid is driven by random partitioning not by mutation. For a high copy number origin, like pUC, this loss is very slow since the odds of a segregant are low.

[Abizar Lakdawalla]

Why grow the bacteria without the Antibiotic? Sorry lost the purpose of the original question. Is it because you don't have Antibiotic plates? Easy way around is to pipette Antibiotic solution directly on the plate and spread it around (sterile swab, hockey stick) and let it dry ...

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[MC]

Thanks for all the replies! I originally had the question because I didn't have antibiotic plates but I've since acquired some, but still it got me thinking about the "what if" situation. Reading about Plasmid Partitioning now!