FRIDAY, April 23, 2004 (HealthDayNews) -- Waste left by chickens raised in industrial chicken houses contains a wealth of bacteria that have antibiotic multi-resistance genes, a new study has found.
Since the development of antibiotics, bacteria have been able to mutate and become resistant to them. In this new study, researchers show how bacteria are able to become resistant to many antibiotics at one time by pasting together genes that are resistant to many antibiotics.
"A genetic element, called integrons, that's involved in pasting together multiple-antibiotic resistance genes has been found in much greater abundance than was ever anticipated," said lead researcher Anne O. Summers, a professor of microbiology at the University of Georgia.
These integrons were found in bacteria where they haven't been found before, she added.
Previously, integrons have been studied only in so called gram-negative bacteria that include the food-borne pathogens such as salmonella, Escherichia coli and other bacteria that can make you sick and even kill you.
But in this new study, which looked at resistant bacteria in the real world, researchers found most of these integrons live in harmless gram-positive bacteria, which are normally found in humans and other animals and do not cause disease. Yet somehow, these integrons are transferred to gram-negative bacteria.
In their study, Summers' team collected samples of poultry litter from several farms over 13 weeks and examined it for resistant bacteria, according to their report in this week's issue of the Proceedings of the National Academy of Sciences.
There are more bacteria that become multi-antibiotic resistant than scientists thought, Summers said.
Of the thousands of bacteria that live in all animal systems, experts now know that genes that make them resistant to many different kinds of antibiotics can be created quickly, as the integrons in both gram-negative and gram-positive bacteria paste together many types of antibiotic resistance genes in each bacteria, she explained.
The problem is that these strings of antibiotic-resistant genes make each type of bacteria safe from many different antibiotics, Summers said.
Summers believes that they will find the same antibiotic resistance mechanism in humans. They are now screening bacteria from humans to see if these samples carry integrons.
"For a long time, antibiotic resistance has been studied one antibiotic at a time, one bug at a time, but looking beyond that we can now see why resistance spreads so fast and why it's so hard to manage it," Summers said.
"We are going to have think about antibiotic resistance in a radically new way if we are going to overcome this problem in a way that leads to health benefits for people to diminish the risk of developing serious infections that are untreatable," she said.
"We are going to have to do some really new thinking," Summers said, "because the bugs are built to respond very cleverly to anything we throw at them." It takes 20 years to develop a new antibiotic, but only two years for bacteria to become resistant to it, she added.
Dr. Stuart B. Levy, president of the Alliance for the Prudent Use of Antibiotics and a professor of medicine at Tufts University, said what's striking is that, up until this finding, integrons were thought to be only in gram-negative bacteria.
"But now we find that they are actually also in gram-positive bacteria," he said. This discovery says that most of these integrons are in gram-positive bacteria, but how they get from there to the gram-negative bacteria is not known, he added.
"In humans this means that maybe some of the bacteria that people normally carry, which are gram-positive, could be housing antibiotic resistance, and we haven't looked at that," Levy said.
To combat the problem of antibiotic resistance, we need to use antibiotics more appropriately, he said.
"We also need to look at ways to prevent the spread of these resistant integrons. And the study also raises questions about whether the use of animal antibiotics has not created the farm as a factory for creating antibiotic resistant bacteria," Levy said.
More information
The Alliance for the Prudent Use of Antibiotics can tell you about antibiotic resistance, and the National Institute of Allergy and Infectious Diseases can tell you more about the antibiotic problem.
