Study finds bacteria have multiple defenses against multiple enemies
Pluck a microbe out of the ground, and it’s likely to be resistant to most antibiotics, a new Canadian study finds.
Researchers at McMaster University screened 480 strains of bacteria they took from soil and tested them against 21 different antibiotics. Every bacterium was resistant to a number of antibiotics, an average of seven or more, according to the report in the Jan. 20 issue of Science.
“The density of resistance is surprising,” said Gerard D. Wright, chairman of biochemistry and biomedical sciences at the university’s Michael G. DeGroote School of Medicine. “Old compounds, new compounds, it doesn’t seem to matter. They have all sorts of ways to get around these things.”
That resistance doesn’t come from exposure to antibiotics used in medical treatment, Wright noted. It’s just the bacteria’s way of surviving in a world full of perils, he explained, since they are surrounded by competing organisms that produce their own natural antibiotics.
“This is giving us a glimpse into very complex organisms that have been living for millions of years,” Wright said. “They have evolved a really complicated set of strategies that allow them to deal with all sorts of threats, old threats and new threats.”
While overuse or just plain use of medical antibiotics is known to increase the incidence of resistance, this study suggests that natural resistance happens without exposure to those drugs, he said.
“We got bacteria from a number of sources — urban environments, agricultural environments, the woods in northern Ontario that has not seen any use of human antibiotics — and the level of resistance was the same,” Wright said.
Most of the genetic mechanisms of resistance seen in the study were already known, but a few new ones showed up, he said. The researchers now are doing more detailed research into the mechanisms by which bacterial alter their genetic function to fight antibiotics.
The study has two practical applications, Wright said. “One is to alert clinicians and medical biologists to new methods of resistance than can emerge in the clinic,” he said. “And for people who make antibiotics, this should give them a heads-up about methods of resistance they may not see in the clinic today, but may see tomorrow. Clever chemistry might delay resistance being a problem,”
But there is no way to prevent antibiotic resistance occurring, because the strategies built up over millennia can’t be dodged completely, Wright said. He noted the researchers found bacteria resistant to telithromycin, one of the newest antibiotics on the market.
“This will just help delay and inform about resistance,” Wright said. “It gives people more ammunition to fight it.”
The finding could also help refine strategies for finding new antibiotics, said Dr. Stuart B. Levy, a professor of medicine at Tufts University Medical School, and president of the Alliance for the Prudent Use of Antibiotics.
A close look at the study shows that many microbes defend themselves by producing enzymes that break down antibiotics, said Levy, who is also the author of The Antibiotic Paradox.
“We may not be finding new antibiotics when we go to the soil to look for them because we don’t take into account that they are being destroyed,” he said. “We may need new techniques to isolate new antibiotics. Maybe we can do a better job finding them by knowing this.”
More information
Antibiotic resistance is explained by the Alliance for the Prudent Use of Antibiotics.
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