This is pointless. You think pvt parts are clean? O.k if a woman rubbed a apple on her leg, tummy or even the top of her feet, would you eat it? Most certainly would. Now If a man rubbed his balls on a apple, would you eat it? or if a woman rubbed herself with the apple on her vagina, still eat it? most will not.
so what ? kissing transfers thousands of bacteria cells, same as sex. sure its not as clean as water but its not killing anyone. Your logic is completely false. Either something is dirty (in case all sex is and it should be banned) or its all good as long as you are careful.