Too early to say.
Most bacteria and viruses that we encounter have co-evolved with us. They rely on our particular body parts and cellular chemistry in order to do their thing.
While its pretty unlikely that you'd be able to find something nutritious to eat on a random planet, it's not at all certain that their particular bugs would do for us.
As for toxic chemicals, well, you're not going to be able to stand on somewhere like Io. But there may be plenty of relatively harmless planets around.
Biting the hand that feeds IT
