Antibiotics are supposed to kill bacteria, not feed them. Yet Harvard University researchers have discovered hundreds of germs in soil that literally gobble up antibiotics, able to thrive with the potent drugs as their sole source of nutrition.
These bacteria outwit antibiotics in a disturbingly novel way, and now the race is on to figure out just how they do it — in case more dangerous germs that sicken people could develop the same ability.
On the other hand, the work explains why the soil does not harbor big antibiotic buildups despite use of the drugs in livestock plus human disposal and, well, excretion, too.
"Thank goodness we have those bacteria to eat at least some of the antibiotics," said bacteriologist Jo Handelsman of the University of Wisconsin-Madison, who was not involved in the study. "Nature's pretty effective."
The discovery, published in Friday's edition of the journal Science, came about almost by accident.
A team led by Harvard Medical School geneticist George Church has a Department of Energy grant to develop ways to create biofuels from agriculture waste. Plants are full of natural toxins, so the goal was to find microorganisms in soil capable of breaking down certain of those chemicals. To winnow down the strongest candidates, they tried exposing these bacteria to what should have been far more toxic substances, antibiotics.
That bacteria can eat weird things is the basis for the field of bioremediation. Some bugs help break down oil spills, for example.
Nor is it a surprise that soil bacteria can withstand some antibiotics; some had already been found. After all, a number of antibiotics are natural — think penicillin. Some antibiotics have been derived from soil.
Instead, the surprise was how many bacteria did not just survive but flourished when fed 18 different antibiotics, natural and manmade ones — including such staples as gentamicin, vancomycin and Cipro — that represent the major classes used in treating people and animals.
Church's team gathered soil from 11 spots in the states of Massachusetts, Minnesota and Pennsylvania, from city parks to pristine forest to a cornfield fertilized with antibiotic-containing manure.
Bacteria prefer to eat sugars, like rotting fruit. Put in laboratory dishes to subsist only on antibiotics, the germs grew a little more slowly but the researchers found every drug tested could support growth of some bacteria.
More disturbing, a number of bacteria could withstand levels of antibiotics that were 50 to 100 times higher than would be given to a patient.
"They were not only resistant, they were super-resistant," Church said.
"I guess we weren't really thinking about it as something that bacteria would just eat for breakfast," he added. "They are capable of living on this stuff for a long, long time."
The finding comes amid increasing concern that many infections could soon become untreatable, as more bacteria become immune to today's antibiotics even as few new drugs are being discovered.
But the medical impact of the new work isn't yet clear. Germs in soil aren't big human threats, and no human pathogen has been spotted with the same ability. Still, many of the soil bacteria tested are relatives of human pathogens, including a notorious E. coli strain.
So the next step, under way now in Church's lab, is to identify the actual genes that let these bacteria devour and degrade antibiotics. Then the question becomes whether that genetic mechanism is something soil bacteria might be able to transfer to human pathogens, thus making them more drug-resistant.
Wisconsin's Handelsman says gene pathways involved in metabolism are far larger and more complex than the type of single-gene resistance often seen in human pathogens. "It's not really as bleak as that."
And Church agrees his work is "not entirely all bad news. ... It gives us some time to get ahead of it and figure out if it really poses a threat."