Although the saliva on dogs' tongues offers some antibacterial protections, calling a dog's tongue antiseptic is a stretch because antibacterial compounds are not the only things to be found in a dog's mouth. Harmful bacteria that are resistant to the antibacterial compounds live alongside them quite comfortably.
The main antibacterial component found in dog saliva is lysozyme, an enzyme specialized for attacking bacteria by breaking up carbohydrates found within the bacterial cell's membrane. This enzyme is found in heightened amounts on dog tongues as compared to human tongues, but is otherwise unremarkable. The enzyme is found in many other animals and in other parts of the body as well.
Dog saliva also contains other antimicrobial measures; for example, it is alkali, which discourages bacterial growth. Nevertheless, dog mouths still contain numerous bacteria and having a wound licked by a dog's tongue has led to septicemia, a dangerous bacterial infection of the blood.