Genetically engineered phages — viruses that kill bacteria — have been used for the first time to treat a patient struggling with a dangerous, persistent superbug infection.

The 15-year-old female patient had been infected with Mycobacterium abscessus, which is in the same genus as the bacterium that causes tuberculosis.

Researchers screened a database of more than 10,000 phages to find those active against the bacterium. They engineered three phages to make them more lethal.

The patient improved after treatment with the phage “cocktail,” according to a study published Wednesday in Nature Medicine.

It is “plausible” that the modified phages were responsible, the study said. But making a firm conclusion wasn’t possible, because only one patient was treated.

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