Last week was World Antibiotics Awareness Week, and a new study in The Lancet Infectious Diseases showed just how dire the antibiotics situation has gotten. Authors from the South China Agricultural University, the China Agricultural University, and other institutions identified a gene that confers resistance to a last-resort antibiotic, and then found that gene in E. coli isolates from 15% of raw meat samples, 21% of pigs about to be slaughtered, and 16% of hospital patients with infections. (The study is behind a paywall, but there’s a helpful summary here.)
The authors warn that given these findings, “progression of Enterobacteriaceae from extensive drug resistance to pan-drug resistance is inevitable and will ultimately become global.” Enterobacteriaceae is a family of bacteria that includes E. coli, Salmonella, and Shigella – bacteria often involved in foodborne illness outbreaks. A strain of multidrug resistant E. coli (ST131) associated with urinary tract and bloodstream infections has already spread around the world. This isn’t the strain in which researchers found MCR-1, but the concern is that strains of bacteria already resistant to multiple drugs could acquire MCR-1 and leave few options for treating infections. As more bacteria acquire resistance to more drugs, we’ll keep getting closer to a “post-antibiotics future” in which cuts, common diseases like pneumonia, and common medical procedures like dialysis and surgeries can easily kill.
The gene in question is called MCR-1, and the antibiotic to which it confers resistance is colistin. Mike the Mad Biologist provides some background on colistin and explains why this gene is such bad news:
First, some background: polymyxins, including polymyxin E also known as colistin, are the last line of defense against antibiotic-resistant Gram-negative bacteria, such as E. coli, Klebsiella, and others. For regular readers, you might remember that I’ve referred to carbapenem antibiotics as the last line. That’s because the efficacy of colistin is debatable: some studies show a very good cure rate, others do not. It doesn’t help that colistin can have severe side effects such as kidney failure. Nonetheless, as carbapenem-resistance enterobacteriaceae (E. coli and pals, often referred to as ‘CRE’) increase, colistin is what we have.
Bacterial resistance to colistin has been seen, but its saving grace, such as it is, is that this resistance is not very transmissible. In other words, a colistin-resistant bacterial strain can spread, but it won’t transfer that resistance into another strain.
Until this paper.
As always on issues of antimicrobial resistance, Maryn McKenna provides helpful analysis:
A thing about colistin, which no one seems to have connected the dots on: Because it is an old drug, it is cheap. And because it is cheap, it is an affordable addition to animal feed for all the uses I’ve talked about before: to make animals put on muscle mass faster, and protect them from the conditions of intensive farming.
Which, apparently, is how it is being used in China—but not only in China.
… There are two problems here. First, that thousands to millions of animals are getting the drug, which exponentially expands the opportunities that favor resistance. And second, that projects such as the Chinese one that allowed the new gene to be discovered are rare—so colistin resistance could begin moving, from animals and into people, without being noticed.
I was also interested to see that this study resulted from “a routine surveillance project on antimicrobial resistance in commensal Escherichia coli from food animals in China.” In the US, we have the National Antimicrobial Resistance Monitoring System (NARMS), a collaborative program of the FDA, CDC, and USDA that gathers data from retail meat and human clinical samples. In August, FDA made NARMS data available online so researchers from outside these agencies can participate in the important effort.
It’s good to know that researchers have tools to identify new or increasingly prevalent strains of antibiotic-resistant bacteria. However, we already have extensive evidence of links between heavy use antibiotics in livestock, development of antibiotic-resistant bacteria, and human infections. What we most need is swift action to stop the routine use of antibiotics in livestock.