Is it bad to eat?

We had Subway for lunch yesterday and well a toasted footlong is too much for little me to eat at once. I put the rest in the fridge ready to eat today and then I thought...if I put this in the microwave or oven it'll heat up the mayo, which isn't that supposed to be really bad to ingest due to it being a breeding ground for bacteria??? So, I'm sitting here hungry for my sandwich but questioning if I should go for it because I don't want to die from a food-borne illness. Well, I'm being really overdramatic but you know what I mean... uh I'm tired of worrying about it, into the trash it goes. I'm not going to chance it but I'd still like to know for future reference though to save me time and hunger haha