How to determine if a bacterial cell is alive

[kaymicro]

I've been having some issues with this question because bacteria can remain dormant so you wouldnt be able to tell, then i read this in the book:
Each cell will undergo multiple rounds of cell divisons to produce separate colonies on the plate, so each cell is a colony forming unit. After incubation the number of colonies will reflect the number of CFUs originally present. This test gives the viable count (living cells only) compared to a microscopic count or dry weight test that gives the total cell count (living and dead cells).

Do you think thats a good answer? Should i add anything else?
Thanks so much

[mith]

The answer that is given is correct but it seems to answer a different question i.e. you won't know which cell is alive but that a live cell once lived there. Are there any live dead assays?

[kaymicro]

But doesnt the viable count only determine living bacteria?
I'm not sure what you mean by live dead, sorry. Do you have any suggesions what i should look under or maybe something online i could read?
thanks

[JackBean]

I think, that what you wrote is actually, what you do not want, because if the cell was dormant, than it probably won't grow
Maybe some staining? There is some staining, which stains only the death cells, but maybe it's only for plants cells, as they have the cell wall (but maybe it could work for bacteria as well)

[canalon]

Yes propidium iodide can be used for live/dead counting, and it relies on cell wall integrity, so dormant cells are not stained.
And there are a few other techniques, like PCR inhibitors that binds to free DNA and can enter dean cells (to be used before cell lysis obviously) which coupled with qPCR is supposed to be able to give a live count only.

But the viable/live/dead bacteria is a problem that has no definitive answer yet and culture is giving a count of Colony Forming Units (bacteria), so of bacteria that can form colonies in the given conditions. With appropriate reviving treatment the number of cfu can be changed. So it all depends on the limits you put to your experiments and what you want to observe.

[mith]

by live dead I mean something like trypan blue which I've used on mammalian cells, it detects broken cell membranes which can mean dead cells.