Several strains of bacteria in the soil can make a meal of the world's most potent antibiotics, researchers said on Thursday, in a startling finding that illustrates the extent to which these germ-fighting drugs are losing the war against superbugs.
A study of soil microbes taken from 11 sites uncovered bacteria that could withstand antibiotics 50 times stronger than the standard for bacterial resistance.
"It certainly was very surprising to us," said George Church, a geneticist at Harvard Medical School in Boston, whose research appears in the journal Science.
"Many bacteria in many different soil isolates can not only tolerate antibiotics, they can actually live on them as their sole source of nutrition," Church said in an audio interview on the journal's Web site.
Other researchers have found antibiotic-eating strains of bacteria, but Church's study is among the most systematic. It offers more clues about why bacteria quickly develop resistance to antibiotics, and why drug companies must constantly develop new antibiotics to defeat them.
Church's team initially set out to find organisms in the soil that remove toxins from cellulose, the material that gives plants structure. They took samples from a variety of sites, including a cornfield fertilized by manure from cows that were fed antibiotics.
Microbes taken from these soil samples could easily defeat toxins from cellulose, which they expected. Then the researchers tested the microbes against antibiotics, something they thought would be toxic.
"We were expecting them to grow on cellulose and we weren't expecting them to grow on antibiotics," Church said.
Surprised by how easily the microbes devoured the antibiotics, Church and colleagues did a broader test, exposing hundreds of microbes to 18 antibiotics representing most of the major classes of naturally occurring and synthetic antibiotics, including penicillin and the widely prescribed antibiotic ciprofloxacin.
"We could find ... bacteria that could grow on almost all of them," depending on the bacteria and the source of the soil, Church said.
The bacteria were not known to attack humans, but some were close relatives, such as members of the Burkholderia cepacia complex, a group of bacteria that infect people with cystic fibrosis, and Serratia marcescens, which can cause blood infections in people with compromised immune systems.
Church said the finding underscores the extent to which bacteria have developed resistance to antibiotics, a process that started almost as soon as penicillin was introduced in the 1940s. Overuse and misuse of antibiotics have since fueled the rise of drug-resistant superbugs.
"This is yet another way of looking at resistance," Church said of the study. He said the microbes he found may be using a new way to disarm the antibiotics, but it may take some time to figure that out.
One antibiotic resistant infection, caused by a strain known as methicillin-resistant Staphylococcus aureus, or MRSA, is blamed for killing 19,000 people in the United States in 2005.