Tuesday, 12 February 2013

Antibiotic resistance in China promoted by farm animal feeding practices

Widespread and unregulated use of antibiotics in animal feed in China is causing the emergence and release of antibiotic resistance genes  to the environment, according to a study that found 'diverse, abundant, and potentially mobile antibiotic resistance genes in Chinese pig farm.
Writing in the Proceeds of the National Academy of Sciences, Chinese and US researchers say that antibiotic resistance genes  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. They say that despite the volume of antibiotics used in China, little information is available regarding the corresponding antibiotic resistance genes associated with animal farms.
Therefore, they assessed type and concentrations of  antibiotic resistance genes 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  antibiotic resistance genes being enriched 192-fold up to 28,000-foldcompared 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 between  antibiotic resistance genes and transposase abundance. In addition, abundance of  antibiotic resistance genes correlated directly with antibiotic and metal concentrations, indicating their importance in selection of resistance genes.
Source: PNAS

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