The Evolution of the Superbugs

In August 2016, a woman in her late 20s arrived in a hospital in Reno, Nevada, carrying a particularly deadly strain of the bacteria Klebsiella pneumoniae. The woman, who recently had traveled to India, and while there was admitted to several hospitals over complications caused by a thighbone fracture, proved to be resistant to all 26 types of antibiotics by the time she was hospitalized in the United States—including carbapenem, often considered the “last resort” antibiotic, because it is used when all other antibiotics fail.

What is a Superbug?

The strain responsible for the woman’s infection,Klebsiella pneumoniae carbapenemase, or KPC, is one of several types of bacteria that have become known as “superbugs”. At least 18 of these diseases and infections have been labeled by the CDC, and three in particular have been classified as “urgent” drug-resistant threats: Neisseria gonorrhoeae, which causes the STD gonorrhea, Clostridium difficil (CDIFF), which causes life-threatening diarrhea, and a class of bacteria known as Carbapenem-resistant Enterobacteriaceae (CREs), which includes KPC.

Of these, CREs are the most worrisome for scientists and doctors. Though no less deadly than other types of drug-resistant diseases, CRE drug resistance is found within genes that lie in plasmids, pieces of DNA that can easily move between bacterial species of the same family. Enterobacteriaceae (The “E” in CREs), a particularly large group of related bacteria that include species such as Salmonella, E. coli, and Shigella, are particularly susceptible to the spread of plasmid-based genes between bacterium. Although all of these diseases are easily treatable with antibiotics, they can quickly prove to be deadly without proper medication.

CREs are particularly prevalent in China and South Asia, but are becoming increasingly more common in the United States as well: the CDC estimates that this year alone, at least 175 cases have been reported in hospitals. Luckily, most CREs can still be cured with a few antibiotics that are used only in extreme cases, but even these may be effective for only so long.

Colistin and the MCR1 Gene

In China, a new variant of a gene, called MCR-1, has been found in cases of Klebsiella pneumoniae and E. coli. Like CREs, Mcr-1 easily moves from one bacterium to another via plasmids, but unlike CREs, this variant of MCR-1 allows bacteria to be resistant to the absolute last resort antibiotic, colistin. The reason is not due to an overuse of the drug in treating illnesses, but because  because China has historically used colistin as an animal growth hormone in livestock feed. As humans consume colistin-fed beef, pork, or chicken, the bacteria in our bodies in turn become used to the presence of the antibiotic, and over time adapt to be able to resist it.

CDC graphic

While China has since made it illegal to use colistin in animal feed as of April of this year, it has also since approved the use of the drug in hospitals in order to tackle a growing number of CRE cases, themselves likely caused by the overuse of carbapenems in agriculture. And as colistin is used more and more, so too will it become more likely for bacteria to evolve a resistance for it in humans, paving the way for a string of superbugs incurable by modern science.

The Threat of SuperBug Evolution

It’s a textbook case of organisms adapting to respond to their environments that has been ignored for decades, with people concerned only with the short-term benefits of overusing antibiotics without looking at the long-term consequences. It’s a problem that Alexander Fleming, the creator of penicillin, warned of it his Nobel Prize acceptance speech, saying, “There is the danger that the ignorant man may easily underdose himself, and by exposing his microbes to non-lethal quantities of the drug make them resistant.”

Without the creation of new forms of antibiotics that can be used to fight future CREs and colistin-resistant superbugs, scientists predict that antibiotic-resistant diseases could kill up to 10 million people a year, mostly from common infections that today are easily treated. The unfortunate reality is that scientists had warned of this scenario since the creation of the first antibiotics, and by not heeding their advice, we have set ourselves up for a future of superbugs that may not be able to be cured by modern science.


For More Information:


  •  Klebsiella pneumoniae: By NIAID (Klebsiella pneumoniae Bacterium) [CC BY 2.0 (], via Wikimedia Commons
  • CRE and antibiotic resistance graphics – courtesy of the CDC.

Article by Devin Windelspecht. Devin is a junior at Northeastern University in Boston MA where he majors in international relations.  Devin is responsible for background work on many of the articles on the site, as well as some science writing.


%d bloggers like this: