The Mayo Clinic just published Ten Things You Should Know About Antibiotic Resistance. The interesting thing about the article is that all ten things actually refer to just one thing: the mcr-1 gene.
Mcr-1 has become the gene of interest in antibiotic circles because (1) it has already conferred resistance on colistin, an antibiotic of last resort and (2) it’s promiscuous: it easily goes from one bacterium to the next leaving “superbugs” in its wake. The upshot, warns the CDC, is that this gypsy gene could turn all species of bacteria into superbugs thereby rendering our antibiotics useless.
To really appreciate what’s happening here we turn to Columbia School of Medicine oncologist, and Pulitzer prize-winning author, Siddhartha Mukherjee MD, and his new and important book, The Gene: An Intimate History. He explains how genes “travel”:
Throughout the biological world genes generally travel vertically — i.e., from parents to children … the gene never leaves the living organism or cell [the body].
Rarely, though, genetic material can cross from one organism to another — not between parent and child, but between two unrelated strangers. This horizontal exchange of genes is called transformation. Even the word signals our astonishment: humans are accustomed to transmitting genetic information only through reproduction — but during transformation, one organism seems to metamorphose into another.
Transformation almost never occurs in mammals. But bacteria, which live on the rough edges of the biological world, can exchange genes horizontally. To fathom the strangeness of the event, imagine two friends, one blue eyed and one brown eyed, who go out for an evening stroll — and return with altered eye colors having exchanged genes.
In fact, it’s even stranger than that. Since bacteria exchange genes between different species, it would be as if, to continue Mukherjee’s analogy, we took our dog out for an evening stroll, and returned with altered eye colors having exchanged genes. Bacteria, writes Mukherjee, are “capable of trading genetic material like gossip, with scarcely an afterthought; free trade in genes [is] a hallmark of the biological world.”
So why are bacteria able to trade genes like gossip while we humans can only do it so cumbersomely through reproduction? For reasons of self-defense and species survival, says MIT-Harvard professor of medical biology, Eric Lander, PhD.
Bacteria have been around for some 3 billion years Lander reminds us. And for that whole time they have been at war with each other as well as with viruses. And what is a bacteria’s weapon of choice? Antibiotics: It is bacteria and other microorganisms that invented them (penicillin from mold, for example); we humans merely discovered their existence. And to defend against these antibiotics — to stay alive — bacteria have had to evolve various mechanisms to defeat them: what we call antibiotic resistance.
And not only have bacteria been perfecting and evolving these resistance mechanisms for 3 billion years, they turn over new generations — new genetic variants — every 20 – 25 minutes.
That’s why, Lander says, when it comes to genetic engineering we sit at the feet of bacteria — they are the experts. You see it in the contrast with us mortals: Our current version, H. sapien, has been around a mere 100,000 or so years. It takes a relative eternity, 20 – 25 years or so, to produce a new generation (of genetic variants), and we have zero ability to trade genes horizontally, i.e., between one person and another.
So back to mcr-1, an antibiotic weapon that has evolved in bacteria. What if it “escapes”? So far it has been found in E. coli in the gut of hospital patients and has defeated colistin, a “last resort” antibiotic.
But what if E. coli engages in genetic “free trade” and hands over its mcr-1 gene to one of our biggest threats, the common hospital and nursing home bug, MRSA, conferring even further antibiotic resistance on this superbug?
(Dr. Lander’s comments are available online at: https://www.edx.org/course/introduction-biology-secret-life-mitx-7-00x-3, Lecture 15: Cloning: Purifying a Gene.)