Antibiotic resistance has been blamed for at least 2 million illnesses and 23,000 deaths in the US. Researchers are especially concerned about the widespread use of antibiotics in raising cattle, pigs, and other animals for food production. The drugs help the animals bulk up, which boosts their value, but experts warn that they can also promote antibiotic resistance. I’ve asked two guest authors, Josh Bloom and Dr. David Shlaes of the American Council on Science and Health, to share their insights on this issue. They warn that more needs to be done to curb the use of antibiotics in food-producing animals.
By Josh Bloom and Dr. David Shlaes
The recent discovery in China of a new gene found in bacteria in both pigs and humans should both infuriate and terrify the public health community. The gene is called mcr-1, and it is responsible for a new, specific type of bacterial antibiotic resistance — precisely the last thing that the world needs at a time when many antibiotics, which once easily cured infections, have stopped working.
Yet, it would be wrong to lay all of the blame on China since they are not alone in adding antibiotics to feed, a long-used practice, including in the US despite the considerable body of scientific evidence that tells us that this is a very bad idea. Adding antibiotics to animal feed makes the animals grow faster but the practice has also clearly paved the way for the formation of mcr-1.
Bacteria have many tricks up their sleeves. One is the ability to transfer genetic information via plasmids — small circular pieces of DNA that are separate from the normal DNA of the bug — which easily carry genes from one bacterium to another, even if the two are unrelated.
In 2008, a scary superbug called NDM-1, short for New Delhi Metallo-beta-lactamase-1, was discovered in New Delhi (hence the name) that was resistant to almost every antibiotic. The one drug we have left that still works against such strains is called polymyxin, an antibiotic that is toxic and so rarely used that many physicians don’t even know how to administer it correctly.
But, sometimes it is the only choice, since it is the last remaining weapon in the antibacterial arsenal.
One strain of NDM-1 bacteria is carbapenem-resistant Enterobacteriaceae (CRE), which is so lethal that roughly half of infected hospital patients will die — an alarmingly high mortality rate.
A scenario in which both of these genes are operating in the same germ is chilling. For example, if a CRE strain also acquires the mcr-1 polymyxin gene, it becomes virtually untreatable. Although such strains are still uncommon, they are spreading. The polymyxin resistance gene is now found in bacteria collected from 15 percent of samples of all raw meat, 21 percent of pigs, and 1 percent of samples from hospital patients with infections. The gene has already been found outside of China, as well.
It is no coincidence that polymyxin resistance is rapidly developing in China, or that it’s occurring primarily in pigs, since the Chinese commonly use low doses of polymyxin as growth-promoting agents.
In microbiology, it’s a given that exposure of bacteria to subclinical doses of any antibiotic will generate bacteria that are resistant to that drug. But, worse still, sometimes this can result in resistance to multiple, unrelated antibiotics simultaneously.
This happens when a different group of bacterial genes creates a nonspecific pumping defense mechanism that enables the bacteria to expel antibiotics that might otherwise kill them. This means that bacteria that have never even been exposed to a given antibiotic can still acquire resistance to it.
Unless we clean up our own act, we have no business lecturing the Chinese about anything. By any measure, we are losing the war against bacteria. Since 2012, the FDA has approved only four new antibiotics, and research in this area is now a fraction of what it was only 20 years ago. Resistance is a relentless, global problem that can only get worse — unless dealt with effectively, and soon.
Studies in Europe have shown that bringing animals to market, without the use of growth-promoting antibiotics, is no costlier than doing so with them, so using these drugs actually provides little benefit, but much risk.
The practice of speeding up antibiotic resistance, just for the sake of producing larger livestock, must stop immediately, here and around the world.