It Took Just Three Weeks for Superbug to Resist Last-Resort Drug, Doctors Say

A 3D illustration of the gram-negative bacteria Pseudomonas aeruginosa
Illustration: James Archer (CDC)

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.

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That was the case with this patient, whose rare liver disease required them to get two liver transplants, the first at age three. Following the second surgery, the patient developed several life-threatening infections, including one caused by P. aeruginosa in March 2016.

Initially, the bug seemed completely vulnerable to the last-resort drug ceftolozane-tazobactam, a combination therapy of two potent antibiotics. But 22 days into treatment, the doctors found a strain of the bacteria in their patient that had evolved resistance to the drug. Other scientists have found that P. aeruginosa can develop resistance to ceftolozane-tazobactam in the lab, but according to the authors, it’s rarely been documented in real-life patients, much less over such a short time.

The treatment was still enough to beat the initial infection, as well as two other infections caused by P. aeruginosa over the next two and a half years. But the case gave the doctors a chance to study up close how it had evolved. So they sequenced and compared the genomes of dozens of samples collected from their patient.

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During that time period, they found, the superbug evolved resistance to the last-resort drug at least three times. These events seemed to happen independently of one another, rather than a population surviving and returning with a vengeance. But they all happened in the same way, caused by one single mutation in the bacteria.

Interestingly, while the mutation did make the bacteria better at fighting the last-resort drug, it also appeared to restore its weakness to some drugs it had previously resisted. That could mean, the authors wrote, that even scary cases like this could be treated by a “potential alternative therapy” that relies on older drugs. The discovery may even help doctors in the future find a way to prevent this particular kind of resistance from showing up in the first place, they added.

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Still, like many a horror-movie monster that won’t stay dead, superbugs have come up with all sorts of tricks that allow them to evade death. And it’s more than possible, if not inevitable, that a strain of P. aeruginosa or another bacteria could someday combine the right mix of mutations that lets it resist last-resort drugs as well as keep its existing invulnerabilities. Just another fun possibility to think about late at night!

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About the author

Ed Cara

Science writer at Gizmodo and pug aficionado elsewhere