The fossil record tells us what types, kinds, and numbers of organisms may have lived in the past, as well as what they ate, what age they lived in,.
Handwashing is one of the most important (and easiest) practices used to prevent transmission of bloodborne pathogens. Hands or other exposed skin should be thoroughly washed as soon as possible following an exposure incident. Use soft, antibacterial soap, if possible.
It's not just the blood-vessels in the mouth that the F. nucleatum can get into, it can also bypass a lot of other cellular barriers such as the blood-brain barrier that keeps bacteria out of your brain, and the placental barrier that guards the passage of substances between a pregnant mother and the foetus.