Aeromonis, or Aeromonas?
Aeromonas is a zoonotic disease, you could have caught it if you slipped on hygiene. I recommend finding a reptile experienced veterinarian, he should have warned you of the danger.
A vet who gives antibiotics to put in water is not worth his weight in salt.
He perscribed an antibiotic that is touch and go, might as well have thrown penicillin at it. Not all aero spp. are susceptible to what he prescribed. 100 percent of all a. caviae are susceptible to trimethoprim-sulfamethoxazole, he should have given you this prepared for sub QT. With such rapid loss of fluids, saline injections should have been administered.
If he claimed the aero was the culprit for an RI, he was wrong. Entrobacter was to blame for the pulmonary distress, aero for the weight loss. Aero was the main threat to the animals well being, this is what finished off your snake.
Sidenote, this knowledge comes from taking nine credit hours of microbiology.