I'm with Andy on this one. Stop at Best Buy or Microcenter and get a new keyboard. You should probably have a backup around anyway.
That keyboard is probably in an environment like an auto repair shop where the workers are required to input or lookup data. If that filth is body oil accumulation, I would not be working on it. I refuse to work in homes that are that filthy. But then, I own the company and can choose who I will or will not work for. For those who need each and every job that comes along, there are always vinyl gloves to wear as a barrier. I buy them in 100 pair packs all the time, especially for working in bathrooms, kitchens and any type of exposed plumbing.
And YES, we do need to be exposed to bacteria to build immunity.