Pig farms contributing to antibiotic resistance.
For decades, health experts have been warning that widespread use of antibiotics in animal agriculture selects for the evolution of antibiotic resistant bacteria. Antibiotic-resistant intestinal bacteria may then be excreted in animal manure and enter the environment. Active traces of the drugs may also be excreted in animal waste, thereby entering the environment and producing more drug-resistant "superbugs" there. When animal manure is deliberately spread on agricultural fields, the problem is even worse. "In China and elsewhere, large amounts of antibiotics are used in the animal industry to promote growth," said researcher Yong-Guan Zhu. "If pathogens in the environment are exposed to these antibiotics and develop resistance, this is clearly a health threat to the general public." In the current study, researchers used mass spectrometry and liquid chromatography to test the soil from farms near nine different pig feedlots near Beijing, Jiaxing and Tianjin, China. Unlike previous similar studies, which looked only for signs of antibiotics, the researchers tested for the antibiotic tetracycline and 10 of its metabolites, which are produced as it is broken down in a pig's body. The researchers also tested bacteria in the soil for genes linked to tetracycline resistance. They detected 15 such genes, and found that their prevalence was directly correlated with the concentration of tetracycline and its metabolites in the soil. The study shows that soils contaminated with agricultural manure "are major reservoirs of antibiotic-resistance genes in the environment," said Xiangdong Li of The Hong Kong Polytechnic University.
