News / Health

    Gene-Swapping Soil Bacteria Harbor Antibiotic Resistance

    Scanning electron micrograph of the Pseudomonas bacteria, one of several harmless bacteria found to harbor resistance genes identical to those found in disease-causing bacteria, undated (Research Center for Auditory and Vestibular Studies at Washington Un
    Scanning electron micrograph of the Pseudomonas bacteria, one of several harmless bacteria found to harbor resistance genes identical to those found in disease-causing bacteria, undated (Research Center for Auditory and Vestibular Studies at Washington Un
    As drug-resistant infections become an increasingly serious threat worldwide, new research show the problem may be spreading right under our feet.
     
    A new study in the journal Science shows that disease-causing germs and harmless bacteria in the soil are exchanging genes that make them resistant to antibiotics — a finding that may have implications for the widespread use of antibiotics in livestock.
     
    Antibiotic resistance among pathogenic bacteria — the kind that make people sick — is one of the most serious problems in medicine today.
     
    “It’s scary the number of pathogens now for which there are either very few or no drugs available to treat them,” says Gautam Dantas, study co-author and Washington University immunologist.
     
    Swapping genes
     
    The bacteria that cause tuberculosis, skin infections, food poisoning and other diseases become resistant to antibiotics either through mutations in their genetic material or by swapping genes with other bacteria.
     
    According to Dontas, even completely different species can swap gene-carrying DNA.
     
    “Bacteria as different as, say, you and I are to a plant, are still able to exchange DNA,” he says.

    Identical genes

    While researchers have long known that dirt is teeming with both harmless and deadly bacteria ready to exchange genes, they didn't know for sure what was happening.
     
    But after analyzing 11 different soil samples, Dontas and his colleagues found about 100 different antibiotic resistance genes.
     
    “Out of those 100 or so genes, seven of them had exactly the same DNA sequence as antibiotic-resistance genes that have been found in a whole bunch of pretty deadly pathogens from around the world," says Dontas, explaining that they cannot yet tell whether the genes came from the pathogens first and jumped to the soil bacteria or vice versa.

    “But I think either scenario is plausible and either scenario, as far as we’re concerned, is scary,” he adds.

    Food animals

    Dontas says doctors know that over-using antibiotics for patients is helping to increase antibiotic resistance.
     
    “What this work says is that we need to now also consider what happens when we dump antibiotics into food animals,” he says.
     
    On many farms worldwide, antibiotics are routinely given to cows, pigs and chickens to prevent disease and help them grow. According to some figures, more antibiotics are used for healthy animals than for sick people, and the drugs often end up in the soil through the animals’ manure. Dontas says the new study shows soil has the potential to spawn or harbor resistance that can jump to human pathogens.
     
    “This is not a distinct habitat," he says. "These transfers can occur, so practices in one environment are going to impact the other environment.”
     
    Limited risk
     
    The Animal Health Institute, which represents livestock drug makers, says antibiotics break down quickly in manure and in soil, and that regulators consider that risk before they approve the drugs. The industry group also notes that antibiotic resistance occurs naturally, so assessing whether its use in livestock has any additional impact would require further study.
     
    While drug makers support regulatory efforts to eliminate the role of antibiotics in the growth of healthy animals, industry-wide eradication of antibiotics, they say, would have worse implications for public health, as it would only increase the number of sick animals in the food supply.

    Steve Baragona

    Steve Baragona is an award-winning multimedia journalist covering science, environment and health.

    He spent eight years in molecular biology and infectious disease research before deciding that writing about science was more fun than doing it. He graduated from the University of North Carolina at Chapel Hill with a master’s degree in journalism in 2002.

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    Comment Sorting
    Comments
         
    by: Factitious from: Planet earth
    September 03, 2012 9:07 PM
    It's absurd to overly-discouraging "abuse" of antibiotics in humans, ostensibly to prevent resistance, while inviting it by feeding the stuff to livestock by the ton, not for actual disease, but for prophylaxis, or just speed weight gain. The situation is just reckless. They even treat turf grasses on golf courses with antibiotics.

    Rules that make sense, instead of rules that benefit the drug and food industries at the expense of human health, are long overdue.

    by: Dr Edo McGowan from: Carpinteria CA
    September 01, 2012 2:05 AM
    Here is something that warrants much more discussion, i.e., the diminution of viable drugs because of growing resistance. The pharmaceutical industry is disinclined to venture into new antibiotics while medicine (both human and animal) is running out of existing drugs because the bugs are gaining increased resistance. I have a great respect for those in veterinary medicine and was married to one of the faculty in the vet school at UC Davis. But a considerable load of antibiotics goes into feed and not necessarily for treatment of infections. But that is not my main point of this comment. One of the principal mechanisms augmenting the spread of resistance comes from the nation's inadequately designed sewer plants and the inadequate water quality standards. Thus these sewer plants are spewing out industrial volumes of these resistant organisms. Sewer plants actually generate these bugs. The Wastewater Research Division, Municipal Environmental Research Laboratory, U.S. Environmental Protection Agency, Cincinnati, Ohio back in the late 1970s did a fairly robust study demonstrating this, see: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC241834/pdf/aem00183-0119.pdf. At the same time the US/EPA was promoting the land application of sewage sludge onto America's farmland as a beneficial and benign enterprise. The study discussing the fact that sewer plants generated antibiotic resistance was removed from the Agency's data base, evidently for political reasons. It would not look good for a "benign" practice to be shown to actually be spreading resistant organisms across the nation's farmland. That study, however, documented that wastewater, treated or untreated, was and is a primary contributor of bacteria to the aquatic ecosystem, hence sewer sludge applied to land would follow. The removed EPA study did note, however, that several prior studies had been conducted which demonstrated that significant numbers of multiple drug-resistant coliforms were released to rivers, bays, bathing beaches, and coastal canals by effluent from sewer plants. Such waters were contaminated by bacteria capable of transferring drug resistance. Later studies working with antibiotic resistant genes would demonstrate that these genes were now found in the nation's drinking water. The issue was of great concern since there was the potential to transfer of antibiotic resistance to a pathogenic species and thence to humans. One must remember that of the longer rivers in the U.S, one city's sewage becomes the next down-river city's drinking water. There was nothing wrong with the 1970s study except it was a an inconvenient truth. It started as a doctoral dissertation and thus needed to pass through doctoral committee clearance, it was proposed to be released in a peer reviewed journal and thus had to be cleared internally by scientific committees within the EPA, and it had to pass peer review for the journal. It passed all these checks and thus there was nothing wrong with the study, yet you will not find any trace of it within the entire US/EPA data base.

    Well, that said, we are losing the contest with antibiotic resistant pathogens and contamination of our water supply is one of the principal issues but it is an issue that is fraught with political bumbling, sleight of hand, and political coverup. Those who sell bottled water, may however see this as a boon.

    by: Veterinarian from: Iowa
    August 31, 2012 1:11 PM
    This is another case of a researcher making claims that are not supported by the data in his study. He couldn't get the claims about antibiotic use in animals through the peer review process - they don't show up in his paper - so he tries to make a splash in the lay press. Antibiotics are not dumped into animals, in fact as a veterinarian I have the luxury of being able to do microbiological testing and epidemiology to determine which antibiotics to use and the best strategy for use to protect both animal health and public health.

    by: Mike from: California
    August 30, 2012 9:16 PM
    It should not surprise anyone that an industry trade groups would deny any connection between the overuse of inappropriate drugs on healthy farm animals and drug-resistant pathogens. Contrary to the industry mouth-piece, scientists report drug compounds in California's coastal waters EVEN AFTER passing through waste-water treatment plants. Many drugs are quite stable and persist in the environment. That's the science.

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