Pigs in a large Chinese plant. Credit: Image courtesy of San'an Never
Read out More and more often it happens that common antibiotics even against everyday infections no longer work. For the pathogens have become resistant to these hitherto most effective weapons of medicine. Researchers in China have identified a source for these resistances as well as an acute threat to medicine worldwide: In dung from large pig farms, they found almost 150 bacterial resistance genes in large quantities. These, they warn, are highly mobile and make pathogenic germs immune to almost all known antibiotics. The rapid development of antibiotic resistance in recent decades is illustrated by Yong-Guan Zhu from the Chinese Academy of Sciences and his colleagues using an example, the bacterium Acinetobacter baumannii. This germ can cause pneumonia and even lethal meningitis. "Within 30 years, this bacterium has evolved from an easily treatable germ that is highly sensitive to antibiotics into a multidrug-resistant pathogen, " the researchers emphasize. In the meantime, the genetic material of this bacterium contains up to 45 different resistance genes that make it immune to many antidotes.

Bacteria fight back with pumps and blockages

Where Acinetobacter and other pathogens have their resistance, is now relatively clear: Above all, the extreme use of antibiotics in animal breeding and animal fattening, but also in medicine, has over time brought more and more residues of these drugs in the environment, such as Researchers report. However, when bacteria, whether pathogenic or harmless, are constantly confronted with these harmful substances, over time they develop countermeasures: they form pumps that remove the antibiotics from their cells, deactivate the drugs by means of special blocking substances, or shield them Cells against penetration of the substances. Once the genes for these resistance mechanisms have been developed, they are easily passed on to other bacterial species by gene replacement. And this is happening right now at an alarming rate worldwide.

The role played by the unrestricted entry of antibiotic residues into many countries, and what makes such genes particularly mobile, has now been explored in China. "In 2007 alone, 210 million kilograms of antibiotics were produced here, of which almost half were used in animal production, " explain Zhu and his colleagues. For their study they searched with the help of modern genetic engineering specifically in the soil and manure of three large pig fattening plants for resistance genes against antibiotics. display

149 highly mobile resistance genes

With alarming results: In the samples were found up to 30, 000 times increased concentrations of a total of 149 different resistance genes, as the scientists report. These genes make bacteria immune to all common antibiotic classes - and help them to all three previously known defense mechanisms against the drugs. And one more thing the researchers noticed: Although the pigs in the individual plants were always given only certain antibiotics, found in the dung and soil always defensive genes against other, not used there species. This shows that these genes are highly mobile and have been intensively exchanged among the bacteria of different areas, say Zhu and his colleagues. The genetic material of the bacteria contained in the samples contain a particularly large number of DNA segments, which facilitate the transfer of the resistance genes.

Further analysis also provided an indication of what could have made these genes so particularly mobile: the pigs in these farms not only had received antibiotics, but also feed supplements containing heavy metals such as zinc, copper and arsenic. These chemicals are said to actually accelerate fattening, but apparently act on the bacteria they come in contact with, according to the researchers. Contact with the heavy metals probably further enhances resistance and gene transfer.

"The variety and frequency of resistance genes we found in this study is alarming, " the researchers emphasize. This clearly shows that the unrestrained use of antibiotics and heavy metals in pig fattening contributes significantly to increasing the risk of resistant germs.

Yong-Guan Zhu (Chinese Academy of Sciences, Beijing) et al .: Proceedings of the National Academy of Sciences (PNAS), doi: 10.1073 / pnas.1222743110 © science.de - === Nadja Podbregar

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