Given the massive amounts of antibiotics coursing through the bodies of our livestock—not to mention its use and misuse by humans—one would think soil would be teeming with the drugs. But this isn’t the case, and now scientists may know why: They’re being devoured by bacteria.
Harvard researchers stumbled upon this finding while trying to find microbes that could convert agricultural waste into biofuels. The scientists wanted to make sure they had a good control—a group of bacteria that didn’t grow at all—so they bathed some of the bacteria in antibiotics. But there was a problem: The bacteria didn’t just survive in the antibiotics, they consumed them. The researchers then gathered soil from 11 sites with varying degrees of exposure to human-made antibiotics (from manure-filled cornfields to an immaculate forest) and found that every site contained bacteria, including relatives of Shigella and the notorious E. coli that could survive solely on antibiotics. And these weren’t just piddling doses—the bacteria could tolerate levels of antibiotics that were up to 100 times higher than would be given to a patient, and 50 times higher than what would qualify a bacterium as resistant.
Concern about antibiotic-resistant bugs has been ramping up lately, but this in-your-face blow brings it to new heights. According to one of the authors, “almost all the drugs that we consider as our mainline defense against bacterial infections are at risk from bacteria that not only resist the drugs but eat them for breakfast.” Moreover, bacteria frequently swap genes with each other, so pathogenic bacteria could develop a palate for antibiotics (if they haven’t already). But bacteriologist Jo Handelsman of the University of Wisconsin, Madison thinks this is unlikely, as “there are much yummier and easier things to eat in the human body.”