Could a microwave oven kill bacteria and viruses?

Not necessarily. Which is why some people get into trouble (get sick) when they microwave raw chicken- the microwaves may not penetrate evenly (unlike heat from an oven), and some germs which are always there are allowed to survive. Microwaves should only be used for warming up food, not for cooking - since they cannot be trusted. Better to use an oven, fire or grill -something that we know kills those germs.