Help!

I noticed yesterday that my Axolotl had skin irritation on his back. So I looked up what was wrong and apparently my axolotls has a disease called Aeromonas hydrophila I think.
Is this contagious?
What do I do to save him?? He wont eat either.

First - it is hard to diagnose some problems from pictures, so what you have diagnosed may not be what is actually the problem. Your best bet is to take him to a qualified amphibian vet. If there isn't one available, if you decide that medicating is necessary, see Axolotls - Health & Diseases for some medications that are axolotl safe - you can probably get them at a fish store if there is one near you. But medicating has risks, so don't rush to it without getting as much info as you can. If you are correct about Aeromonas hydrophila, Wikipedia says it is gram negative, so you would want an antibiotic that is good against gram negative bacteria.

Second - Regardless of what the "problem" is, most axolotl problems are directly or indirectly related to poor water quality. So

===> What are your water parameters? Ammonia, nitrite, nitrate, pH and temperature?

===> What are you feeding him?

===> How long has he not been eating?

===> Have there been any "tank" problems? (like, filter died, long power outage, went-on-vacation-and-someone-overfeed, etc.)