According to this article, not all germs are bad:
Also, many bacteria have co-evolved with humans to form a simbiotic relationship with our bodies (think of the mitochrondria in every cell that aids in aerobic metabolic processes and the bacteria that line our GI tract that help digestion).
Here is an easy-to-follow decision tree about when to eat food after you've dropped it on the ground:
Scientists have actually shown that ingesting more germs can help your immune system ward off infections. This knowledge is the basis for all vaccinations and flu shots. If you didn't know, these are harmless doses of the virus that will allow your body to develop the defense mechanisms needed in the potential future.