Gut and vag flora are largely similar since one is colonized by the other. Therefore, eating ass is a feasible conduit of transmission, however that assumes the hosts gut flora is healthy and that the balance has not been disturbed by things like antibiotics or poor diet. The much more strictly controlled environment of the vag ensures that flora are less prone to the imbalances that can plague the gut.
Pen on the other hand is covered with fungus, which behaves antagonistically toward gut bacteria and can also cause thrush. Pen juice is sterile though and actually slightly basic, which is why it burns your throat or god forbid your eye if you get it there. As a base, it neutralize the acidity of the vag creating harsh conditions for the resident flora.
So while eating as is an okay way to subsidize struggling gut colonies, sucking dick will have no effect at best and at worst it would be mildly counter productive while giving you a sore throat.
i hope this helps.
