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AFD - PNAS: Abundant Antibiotic Resistance Genes In Chinese Swine Farms

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  • AFD - PNAS: Abundant Antibiotic Resistance Genes In Chinese Swine Farms

    hat tip Michael Coston

    PNAS: Abundant Antibiotic Resistance Genes In Chinese Swine Farms

    Inoculated MacConkey agar culture plate cultivated colonial growth of Gram-negative, small rod-shaped and facultatively anaerobic Klebsiella pneumoniae bacteria. ? CDC PHIL.

    # 6928

    We?ve discussed the emergence of antibiotic resistant bacteria often in this blog (see here, here, and here for a few examples), and it has been a mainstay of Maryn McKenna?s always excellent Superbug Blog.
    The reckless and unrestricted use of antibiotics threatens to render our antibiotic arsenal useless, and many warn that in a few years we could be thrown back into a `pre-antibiotic era?, where even simple infections are once again deadly.
    Today, a study appears in PNAS that illustrates just how damaging the unrestricted use of antibiotic used in agriculture can be, with an examination of the staggering number of antibiotic resistant genes (ARGs) found in swine manure in three locations in China.

    First, the press release from the Michigan State University, then a link to the PNAS article, followed by comments from Professor Peter Collignon, an infectious diseases expert from the Australian National University.
    Published: Feb. 11, 2013
    Unchecked antibiotic use in animals may affect global human health

    Contact(s): Layne Cameron , James Tiedje
    The increasing production and use of antibiotics, about half of which is used in animal production, is mirrored by the growing number of antibiotic resistance genes, or ARGs, effectively reducing antibiotics? ability to fend off diseases ? in animals and humans.

    A study in the current issue of the Proceedings of the National Academy of Sciences shows that China ? the world?s largest producer and consumer of antibiotics ? and many other countries don?t monitor the powerful medicine?s usage or impact on the environment.

    On Chinese commercial pig farms, researchers found 149 unique ARGs, some at levels 192 to 28,000 times higher than the control samples, said James Tiedje, Michigan State University Distinguished Professor of microbiology and molecular genetics and of plant, soil and microbial sciences, and one of the co-authors.

    ?Our research took place in China, but it reflects what?s happening in many places around the world,? said Tiedje, part of the research team led by Yong-Guan Zhu of the Chinese Academy of Sciences. ?The World Organization for Animal Health and the U.S. Food and Drug Administration have been advocating for improved regulation of veterinary antibiotic use because those genes don?t stay local.?

    Antibiotics in China are weakly regulated, and the country uses four times more antibiotics for veterinary use than in the United States. Since the medicine is poorly absorbed by animals, much of it ends up in manure ? an estimated 700 million tons annually from China alone. This is traditionally spread as fertilizer, sold as compost or ends up downstream in rivers or groundwater, taking ARGs with them. Along with hitching rides in fertilizer, ARGs also are spread via international trade, immigration and recreational travel.
    (Continue . . . )

    The Abstract from PNAS (the entire article is available).

    Diverse and abundant antibiotic resistance genes in Chinese swine farms

    Yong-Guan Zhu, Timothy A. Johnson, Jian-Qiang Su, Min Qiao, Guang-Xia Guo, Robert D. Stedtfeld, Syed A. Hashsham, and James M. Tiedje

    Antibiotic resistance genes (ARGs) are emerging contaminants posing a potential worldwide human health risk. Intensive animal husbandry is believed to be a major contributor to the increased environmental burden of ARGs. Despite the volume of antibiotics used in China, little information is available regarding the corresponding ARGs associated with animal farms.

    We assessed type and concentrations of ARGs at three stages of manure processing to land disposal at three large-scale (10,000 animals per year) commercial swine farms in China. In-feed or therapeutic antibiotics used on these farms include all major classes of antibiotics except vancomycins. High-capacity quantitative PCR arrays detected 149 unique resistance genes among all of the farm samples, the top 63 ARGs being enriched 192-fold (median) up to 28,000-fold (maximum) compared with their respective antibiotic-free manure or soil controls.

    Antibiotics and heavy metals used as feed supplements were elevated in the manures, suggesting the potential for coselection of resistance traits. The potential for horizontal transfer of ARGs because of transposon-specific ARGs is implicated by the enrichment of transposases?the top six alleles being enriched 189-fold (median) up to 90,000-fold in manure?as well as the high correlation (r<sup>2</sup> = 0.96) between ARG and transposase abundance. In addition, abundance of ARGs correlated directly with antibiotic and metal concentrations, indicating their importance in selection of resistance genes.

    Diverse, abundant, and potentially mobile ARGs in farm samples suggest that unmonitored use of antibiotics and metals is causing the emergence and release of ARGs to the environment.

    And lastly, a radio interview with Professor Peter Collignon, on Australia?s ABC Radio Network, where he states that this study provided, `bigger and larger numbers than even I would have expected and it just shows how we really have to take better stock of what we do.?

    Follow the link for the transcript and audio file.