A dangerous new form of antibiotic resistance has spread to the United States, according to a report published Thursday. Researchers at the Department of Defense announced that a Pennsylvania woman developed a urinary tract infection (UTI) with bacteria that fought off an antibiotic of last resort called colistin, and had 15 genes for resistance to other antibiotics. Until now, many bacteria have been vulnerable to colistin, even if they have been able to survive other medications. Since this type of resistance can easily spread between bacteria, the findings have sounded alarm bells among scientists over fears that common infections will soon be untreatable.
Bacteria have exhibited colistin resistance in the past, but this time it is different: Previous forms of the resistance weakened the microbes, and the resistance genes were located on DNA that was not easily shared among bacteria. But in November 2015, Chinese and British researchers discovered that mcr-1, a new gene for colistin resistance, was circulating among animals and people in China and was housed on a circular piece of bacteria DNA called a plasmid. Bacteria carrying this plasmid can share copies of it with other bacteria when they come into contact, which allows the colistin resistance to spread widely and rapidly. Because colistin is commonly used in food animals in China, but not in people, “the emergence of mcr-1 likely occurred because of extensive use of colistin in food animal production—which is yet another example of how injudicious use of antimicrobials comes back to hurt us,” explains James Johnson, an infectious disease specialist at the University of Minnesota.
Soon after the Chinese study was published, researchers in Europe and Canada announced that they had found mcr-1-mediated colistin resistance, too. And now, thanks to newly launched Department of Defense surveillance efforts, it has been discovered here in the U.S. as well. In May researchers at the Walter Reed Army Institute of Research and the Walter Reed National Military Medical Center began testing drug-resistant Escherichia coli bacteria isolated from U.S. patients who had been treated at various institutions. That is when they identified the first instance of mcr-1-mediated colistin resistance in bacteria, collected from a woman treated for a UTI in late April at an outpatient military medical center. It also seems to have reached America’s livestock: In a blog post published on Thursday, the U.S. Department of Agriculture and the Department of Health and Human Services announced that they had discovered colistin-resistant bacteria in a sample taken from the intestine of an American pig.
People may pick up these bacteria in various ways, including from their food. Although the types of E. coli that cause UTIs are found within the urinary tract, they typically end up there because they have migrated from the gut. Research suggests that these types of E. coli often contaminate raw meat; in 2010 the National Antimicrobial Resistance Monitoring System, a collaborative governmental project, reported that more than 75 percent of retail chicken and turkey meat was contaminated with E. coli and that many of these bacteria were resistant to multiple antibiotics. A separate 2011 study based on this data reported that more than one-fifth of E. coli found on poultry meat were of the type that can—if ingested when food is not cooked properly—migrate from the gut and cause serious infections such as UTIs.
Ultimately, the big fear is that the newly discovered mcr-1 gene will end up being picked up by other multi-drug-resistant bacteria--particularly a kind known as Carbapenem-resistant Enterobacteriaceae, or CRE. These microbes are resistant to a class of drugs called carbapenems, which are reserved to treat certain resistant infections. Infections with CRE are “becoming more and more common,” says Lance Price, a microbiologist who directs the Antibiotic Resistance Action Center at George Washington University’s Milken Institute School of Public Health—and right now, colistin is among the only drugs that can cure them. If CRE end up intermingling with bacteria containing the mcr-1 gene inside a person or animal’s gut, or even on a piece of meat—and this could already be happening unbeknownst to anyone—the world could suddenly be faced with pan-drug-resistant bacteria. “Then it’s a royal flush—the infection has an unbeatable hand,” Price says. “It’s untreatable."