When we had this problem it kept coming back despite different antisceptics and antibiotics. The vet eventually recommended Manuka Honey in conjunction with any treatment, which worked well for us using hospital human grade antibiotics to clear the infection before lip fold surgery, then after the surgery until the stitches were gone. A complete success with no further occurrence.
Its been 3 years now since we lost him to unrelated problems, missed every day, only just had the heart to look in on here again.