Because bacteria can exchange genes with each other, there is a danger that antibiotics will increasingly lose their effectiveness in treating infectious diseases in humans as well, researchers write in the "proceedings" of the U.S. National academy of sciences.
According to the authors around yong-guan zhu from the chinese academy of sciences, china is the world’s largest producer and consumer of antibiotics. The use of the drugs was not controlled in animal husbandry. This often led to the use of coarse amounts for the treatment of illnesses, but also for growth requirements. Residues were then also found in the manure and entered the soil through it.
To investigate the exact consequences of antibiotic use, zhu and his colleagues took manure, compost and soil samples from three large-scale pig farms in three areas of china. In total, they found 149 different resistance genes that can, in principle, make bacteria insensitive to all major classes of antibiotics. Concentrations of the 63 most prevalent resistance genes averaged 192-fold above control samples, such as virgin forest soil or antibiotic-free manure. In some cases, the concentration was 28,000-fold higher, the scientists report.
In further investigations, they found that the amount of so-called transposases in their samples was also increased. These are enzymes that play a role in the transfer of resistance genes. Simultaneous accumulation of resistance and transposase genes increases the risk of transferring resistance genes from livestock to bacteria that can cause disease in humans, researchers write.
"The resistance genes can reach the general population through food, drinking water or contact with farm workers," explains james tiedje from michigan state university, who led the research team. "Because of this undesired spread, the resistance genes pose a potential threat to human health worldwide. They should therefore be classified as pollutants."
In this context, the german friedrich loeffler institute points out that the detection of such transposase genes alone says nothing about the actual transmission of resistance genes.
In europe, antibiotics may only be administered in animal husbandry for the treatment of diseases. The use for performance enhancement or growth demand is basically forbidden.