Just in time for Halloween, doctors in France say they witnessed a real-life horror tale involving an antibiotic-resistant superbug. In less than a month, their patient’s infection evolved resistance to the last-resort drug they had used to treat it. Thankfully, the doctors were still able to defeat the microscopic threat—and the case may have uncovered a peculiar weakness in the germ.

According to the report, published in the journal Antimicrobial Agents and Chemotherapy, a young child had been dealing with recurrent infections of the bacteria Pseudomonas aeruginosa for over two years. P. aeruginosa is an opportunistic infection that sickens tens of thousands of already weakened people in hospitals and other health-care settings in the U.S. a year. In these people, it can cause serious infections.