The team found three bacteriophages that could be useful (including one from a rotting eggplant) and modified them to maximize their ability to target and wipe out the bacteria strain. Once this was ready, they gave the teen twice-daily infusions as well as surface treatments on the skin lesions resulting from the infection.

The treatment didn’t amount to a cure, but it did have dramatic (and likely life-saving) results. The infection has nearly vanished, according to NPR, and the teen is now healthy enough to resume a mostly normal life — really, the main goal. There also weren’t side effects.

It could be a long while before you see this kind of treatment happening on a regular basis. There’s still more work to be done determining the efficacy of bacteriophages (gene-modified or otherwise) and whether or not they’re truly safe to use. However, this hints that gene tweaking could one day tackle a variety of stubborn infections, providing a second chance for people who’d otherwise be resigned to a grim fate.

FDA Commissioner Scott Gottlieb stressed that the genetic changes had been deemed safe for the animal, safe to eat and wouldn’t have a “significant” impact on the environment. AquaBounty’s modifications use DNA from other fish to grow salmon at a faster rate, raising concerns about contamination. However, they’re also bred to be female and sterile, theoretically eliminating he possibility that they’ll breed with wild salmon.

The salmon will take a while to reach the market if everything goes according to plan. Aquabounty chief Sylvia Wulf told the AP she expected certification for an Indiana growing facility in “weeks” and could receive eggs soon afterward, but it would take about 18 months for the salmon to reach their target weight.

Whether or not that happens still isn’t completely certain. An alliance of public interest, environmental and pro-fishing groups is in the midst of suing the FDA to overturn the approval on safety grounds. Groups like the Center for Food Safety have argued that regulators haven’t properly assessed the ecological and health risks of the salmon, and have pointed to problems with AquaBounty’s environmental record. If those objections hold in court, the FDA and AquaBounty could go back to square one.