I’m nowhere near as well educated on the subject, but it’s my understanding that human saliva ( as well as tears and mucous) contains an enzyme called Lysozyme, which literally dissolves the bacteria. It’s common in most animals, which is why animals lick their wounds. I’m probably oversimplifying (had some pathology and microbiology classes over 25 years ago) so please forgive if I’m inaccurate. Also, please be gentle, I’m having a bad day.