I was reading last week (may have been on New Scientist - I don't recall) that a new theory for the high incidence of MRSA in British hospitals is excessive hygiene - rather than poor hygiene.
The suggestion was that doctors shouldn't use alcohol gels before visiting patients. Rather, they should immerse their hands in live yoghurt. This would have the effect of coating their hands with lots of "good" bacteria and so provide far less opportunity for other opportunistic bacteria to take hold... they would have to compete with the existing ones for resource, space, etc.
My idea is that there probably exists an opportunity for somebody to start selling "pro-biotic" handwashes and kitchen cleaners for households.
Remember, folks, you saw it here first...