This article originally appeared on Tonic.
The discovery of penicillin is one of the great stories in science history: Scottish researcher Alexander Fleming discovered that the bacteria wouldn't grow near a mold that had appeared in an open petri dish. That mold turned out to be penicillium, and it was later developed into the first antibiotic that allowed us to save countless lives from infections.
Shortly after that discovery, however, bacteria began to fight back. In the decades since antibiotics came into widespread use, many strains of bacteria have developed resistance to penicillin and the other antibiotics that were developed in its wake. The problem has grown so dire that the World Health Organization has warned, "We are heading for a post-antibiotic era, in which common infections and minor injuries can once again kill."
This past Saturday, the WHO released—for the first time—a list of the 12 bacteria they've determined to have the most urgent need for new antibiotic treatments. The list was topped by three bacteria deemed "critical" priority, followed by six more at high priority, and another three at medium priority. Beginning last July, 70 experts in infectious diseases and public health weighed the relative danger of these bacteria, including how prevalent antibiotic resistance is within these strains, how contagious they are, how treatable the infection is, and whether there are any potential new drugs to fight them in the pipeline.
The three most critical bacteria, if you're collecting their trading cards, are Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacteriaceae (which includes bugs you've probably heard of like Salmonella and E. coli). All three are resistant to powerful carbapenem antibiotics, which are considered the last line of treatment to stop an infection. The Enterobacteriaceaeare also resistant to the newest generation of cephalosporin antibiotics.
"Those top three bacteria cause infections that are particularly hard to treat in hospitals, in nursing homes, and in patients who are on things like ventilators," says Suzanne Hill, director of the Department of Essential Medicines and Health Products at the WHO. It's not clear whether these antibiotic-resistant bacteria spring out of hospitals and clinics, or if they're already in the population and prey on the most vulnerable among us. It's possible that you even carry one of these antibiotic resistant bacteria around with you right now, and it only unleashes its destruction when your immune system can no longer keep it down—like if you're undergoing chemotherapy for cancer.
The WHO's list is meant to guide pharmaceutical companies, academic institutions, and government research centers to direct and coordinate their efforts to attack these infections. So far, the pace of new antibiotics hasn't kept up with resistant strains of pathogens, and it's not hard to understand why. The general thinking among scientists is that overuse of antibiotics has helped bacteria become resistant. So while new drugs are essential, anything that's developed would need to be deployed only in the most severe circumstances. "What you want here is a company to develop a drug, and only use it from time to time, which is not the way the pharmaceutical market usually works," Hill says.
Beyond developing stronger antibiotics, what may finally solve the problem of super bacteria is an entirely new approach to the way we fight microbial infections. That could include better vaccines or improved methods to sterilize environments and prevent pathogens from spreading. Or scientists could find another avenue to attack bacteria at the cellular level—one that probably won't be stumbled upon when someone leaves their petri dish open.
"The challenge for the basic scientist is, are there other things that we could could think of now, knowing more about the way cell biochemistry works when we first discovered antibiotics?" Hill says. "That would give us new mechanisms and new ways of targeting these bacteria that are more effective than what we have now."