When bread begins to smell sour it usually means that the bread is bad or going bad and should really be thrown out.
Bread should not have a sour smell to it when it's good and fresh so any bad or sour smell to the bread means that it has gone bad and shouldn't be eaten.
If you do happen to eat sour smelling bread or bread that smells like vinegar then you likely will just get a stomach ache and maybe diarrhea, vomiting, bloating etc.
You may feel really bad after eating the sour smelling bread but it's unlikely to make you deathly ill.
Still if the bread smells sour I would not want to eat it and it probably would not taste good at all.
Best thing to do is eat the bread while it still smells good and if it smells sour or has any mold on the bread then throw it out.
It's not worth getting sick for.
Bread usually lasts around 7 days before it goes bad but it can sometimes last a bit longer depending on the humidity and temperature in the home where the bread is stored.