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Pseudomonas aeruginosa strains resistant to antibiotics can cause severe infections in people with weakened immune systems.

Janice Haney Carr, CDC/Flickr (CC BY-NC-SA 2.0)

Meet WHO’s dirty dozen: The 12 bacteria for which new drugs are most urgently needed

You may never have heard of Acinetobacter baumannii, Pseudomonas aeruginosa, or the Enterobacteriaceae—but these three killers top a new list, drawn up by the World Health Organization (WHO) in Geneva, Switzerland, of bacteria for which new drugs are desperately needed. Unveiled today, the list contains 12 bacteria and bacterial families, with the top three making up the category “critical.”

The list “is not meant to scare people about new superbugs, but to signal to researchers and pharmaceutical companies what their priorities should be,” Marie-Paule Kieny, WHO’s assistant director-general for health systems and innovation, told a press conference today. The crucial drugs are unlikely to be big moneymakers for companies that develop them, she notes, so governments and health agencies need to cooperate to boost the chances that they will be developed in time.

Doctors, researchers, and health officials have been sounding the alarm for years about the rise of antibiotic resistance. The list, developed by researchers at the University of Tübingen in Germany, took into account the level of resistance each class of pathogen has already acquired, how deadly it can be, how widespread, and the burden it causes to health systems.

The top three are all gram-negative bacteria that are resistant to multiple drugs. They aren’t widespread yet, but they do cause severe, frequently deadly infections in hospitals, especially in people who are already immune compromised—including transplant recipients, chemotherapy patients, and elderly people. Just last month, for instance, a woman in Nevada died of an infection with a so-called CRE, or carbapenem-resistant Enterobacteriaceae. These bacteria can cause deadly infections if they take up residence in the respiratory system or bloodstream. The most dangerous strains have recently acquired resistance to a class of antibiotics called carbapenems, the only group that still killed them effectively.

Nine more pathogens round out the agency’s dirty dozen: Six are listed as high priority, including drug-resistant strains of Neisseria gonorrhoeae, which causes gonorrhea, and food-borne agents like Salmonella and Campylobacter. Bacteria in this category cause infections that are less deadly than those caused by the three critical-level bugs, but they are much more widespread. Three “medium” priority organisms all are susceptible to some drugs, but are increasingly becoming resistant.

The list “sets priorities in the right direction,” says Petra Gastmeier, head of the Institute for Hygiene and Environmental Medicine at Charité University of Medicine Berlin, who wasn’t involved in the development of the list. 

In the current market, antibiotics aren’t an attractive investment, Kieny says. When used properly, the drugs are taken only for a short time, so they don’t bring in the high returns that drugs for chronic diseases do. “And rather than trying to maximize sales, we need to restrict usage,” Kieny says, to delay the inevitable emergence of resistance. Part of the solution will be finding new ways to reward companies for developing antibiotics, Kieny says. One idea is to agree to pay companies a big up-front fee, or “prize” as soon as a new drug comes on the market, with guidelines in place so that it would be used sparingly. But governments or other donors would have to agree to pay for the prize money. 

One drug-resistant bacterial pathogen is notably absent from the list: Mycobacterium tuberculosis. The problem of drug-resistant tuberculosis (TB) is "already a globally established priority," the report says; the goal was to increase attention to threats not yet widely recognized. But the TB Alliance, a nonprofit research and advocacy group based in New York City, calls on WHO to reconsider. "The absence of TB from this list is shocking,” the alliance's President and CEO Mel Spigelman said in a statement yesterday. "Every global effort to address the burgeoning AMR [antimicrobial resistance] emergency must include TB." In a response , WHO Director-General Margaret Chan emphasized that "[a]ddressing drug-resistant TB research is a top priority for WHO and for the world." 

WHO released its list ahead of a meeting of G20 health experts this week in Berlin, where the topic of antibiotic resistance is high on the agenda. The focus is appropriate, Gastmeier says. “This is not a problem that we can solve at a national level, and it is one in which low- and middle-income countries are linked to high-income ones.” A prime example: The woman who died in Nevada had spent time in India, where she most likely acquired the resistant strain.

*Update, 1 March, 10:35 a.m.: This item has been updated to include a statement from the TB Alliance and additional comments from WHO.