There are studies in the works which test whether dog saliva can be helpful to our health. It is beginning to look as though the saliva from a dog lick could contain good probiotics and, "Researchers have found positive news that introducing healthy bacteria in the gastrointestinal system seems to help other inflammatory gastrointestinal diseases such as Crohn's disease but that the research on bacteria's influence on our immune system is new." Dogs lick things and lick people and "it could help explain what is happening with bacteria when [people are] living with an animal."
One report stated that it looks like dog saliva has more probiotics than yogurt.
So don't be so quick to be repulsed when a dog wants to give you a big lick.