Two questions about microwave cooking.
- Why does bread take on that particular texture when you over microwave it?
- Does cooking in a microwave kill food born bacteria better than a conventional oven?
Bread and cakes cooked in a microwave get that close-grained texture because it takes time for the bubbles produced by either the yeast or the baking powder to develop properly, and a microwave tends to cook the dough or batter before the bubbles have had a chance to establish themselves and lighten the dough.
As far as killing bacteria, it doesn’t matter what your heat source is, whether it’s a microwave or a gas burner or a campfire. The trick is, though, if you’re trying to make water safe to drink, it has to boil for 20 minutes straight, and it’s hard to do this with a microwave. What kind of bacterial situation are you talking about? Just warming up a plateful of leftovers? Or cooking an entire scalloped potato casserole from scratch?
Don’t cook any food. If you get food poisoning, just put yourself in the oven or microwave for twenty minutes. 
The OP isn’t so much about baking bread in the microwave, as reheating it for too long (if I’m reading it right). I’ve noticed the problem too, but I don’t have an explanation. Reaheating bread ten or twenty seconds refreshes it wonderfully, but do it longer and it turns to leather. Microwave Gourmet by Barbara Kafka has
She doesn’t say exactly what it is about gluten that causes the problem in the microwave.
I don’t know about bread, per se, but microwave-reheated pizza can get soggy. Two solutions I’ve found are to nuke it at lower power for a longer time, or (better, but slower) to microwave as normal, then stick it in the broiler for about 30 seconds.
Yes, I was asking about reheating bread in the microwave, not baking it from scratch. The bread becomes very chewy while it is still warm but becomes brick like once it has cooled off again. Over microwaving other foods does not seem to change the basic texture of the food as drasticly as what happens to white bread.( The timer on my micro doesen’t work. Sometimes I forget the thing is on.)
As for bacteria I was thinking about reheating leftovers. My therory is that a microwave would kill bacteria more efectively at lower tempratures because of the way microwaves heat food. They exite the water molocules in the cells of whatever you are nuking. Wouldn’t this kill bacteria cells not only by heating them but also be bursting the cell walls with steam?
Once it got to the point where the protoplasm started boiling in every cell, I’d imagine the food would’ve already exploded.