Bacteria shares antibiotic resistance with genetic partners

When one antibiotic is used, resistance to many antibiotics can increase

Michigan State University researchers have uncovered a troubling trend towards multiple antibiotic resistance in concentrated animal feeding operations.

A research team led by James Tiedje, distinguished professor of microbiology found that in large swine farms where antibiotics are used continuously in feed for growth promotion and disease prevention, multidrug-resistant bacteria are likely the norm rather than the exception.

In studying large-scale swine farms in China and one population of pigs in the U.S., the researchers confirmed the presence of many partner genes — resistance genes and mobile genetic elements found together.

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When one gene increased or decreased in abundance, partner genes increased or decreased in nearly identical fashion.

Some of these partner genes can make bacteria resistant to antibiotics that were not even fed to the animals. So when one antibiotic is used, resistance to many antibiotics can increase, the scientists report in a study published in mBio.

“In the fight against the rise of antibiotic resistance, we need to understand that the use of one antibiotic or, in some cases, antibacterial disinfectants may increase the abundance of multidrug-resistant bacteria,” he said.

“Tracking the source of antibiotic resistance is quite complicated because antibiotic use, which increases the occurrence of resistance, is widespread, and antibiotic resistance can spread between bacteria.”

The Chinese farms are quite close to large cities. So controlling antibiotic resistance in pigs and farms is important to minimizing human risk, he said.

“This is a global issue rather than one that’s simply isolated in China; multidrug resistance is just a plane ride away,” Tiedje added. “This is why our work in China is definitely as relevant as in the United States.”

They also found that at the Chinese farms, there were up to 14 partner genes, all occurring together in farms that are thousands of miles apart, said Tim Johnson, lead author with MSU’s Center for Microbial Ecology. “These genes confer resistance to up to six kinds of antibiotics, and some allow bacteria to reshuffle the order of their genes.”

In Chinese soils that received manure-based fertilizer, the same resistance genes were found in manure and in high abundance. However, the kinds of bacteria present in soil were quite different. This indicates that on the Chinese farms, the potential for resistance gene transfer among environmental bacteria is likely, said Yongguan Zhu, co-author from the Chinese Academy of Science.

Additional MSU researchers contributing to this study included Robert Stedtfeld, Qiong Wang, James Cole and Syed Hashsham.

Torey Looft, with the USDA’s National Animal Disease Center, and Yong-Guan Zhu, of the Chinese Academy of Sciences’ Institute of Urban Environment and Research Center for Eco-environmental Sciences, also contributed to this study.

The research was funded by the United States Department of Agriculture and Natural Science Foundation of China.

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