Both have a certain quantity and different strains of healthy bacteria (flora) that is necessary for our guts...one, the probiotic, is there to replace the good bacteria after a run of antibiotics, the other is supposed to 'prepare' your guts for when you start a run of antibiotics...not being a professional, I suppose that they are different strains in different quantities.

Here in France, traditionally, they give you brewer's yeast along with any antibiotic treatment and encourage you to eat yogurt before, during and after your treatments.

We also eat a lot of cheeses that are made from non-pasteurized milk...(something that is not usually possible in the States)...

We also drink a lot of bacteria-rich drinks... 

There are other natural ways to encourage the 'happy' bacteria in your guts like using the cooking water from vegetables that you allow to sit for 24hrs (not more) before drinking it...

I have learned that if you take any pro or prebiotics while taking antibiotics that you should take it 4hrs after the antibiotics in order to not destroy their effectiveness. 

Sharon