Manure from dairy cows, which is commonly used as a farm soil fertilizer, contains a surprising number of newly identified antibiotic resistance genes from the cows' gut bacteria.
The findings, reported in mBio® the online open-access journal of the American Society for Microbiology, hints that cow manure is a potential source of new types of antibiotic resistance genes that transfer to bacteria in the soils where food is grown.
Thousands of antibiotic resistance (AR) genes have already been identified, but the vast majority of them don't pose a problem when found in harmless bacteria. The real worry is when these genes appear in the types of pathogenic bacteria that cause food-borne illnesses or hospital infections.
"Since there is a connection between AR genes found in environmental bacteria and bacteria in hospitals, we wanted to know what kind of bacteria are released into the environment via this route," of manure fertilization, says Fabienne Wichmann, lead study author and former postdoctoral researcher at Yale University in New Haven, Connecticut.
Farmers use raw or composted cow manure on some vegetable crops, which could lead to a scenario where residual manure bacteria might cling to produce and they or their genes might move to the human ecosystem. "Is this a route for movement of these genes from the barn to the table?" asks Jo Handelsman, senior study author and microbiologist at Yale.
The first step toward an answer was surveying which AR genes are present in cow manure. Handelsman's team used a powerful screening-plus-sequencing approach to identify 80 unique and functional AR genes. The genes made a laboratory strain of Escherichia coli bacteria resistant to one of four types of antibiotics—beta-lactams (like penicillin), aminoglycosides (like kanamycin), tetracycline, or chloramphenicol.
Roughly 75% of the 80 AR genes had sequences that were only distantly related to AR genes already discovered. The team also found an entire new family of AR genes that confer resistance to chloramphenicol antibiotics, which are commonly used to treat respiratory infections in livestock.
"The diversity of genes we found is remarkable in itself considering the small set of five manure samples," says Handelsman, who is also a Howard Hughes Medical Institute Professor. "But also, these are evolutionarily distant from the genes we already have in the genetic databases, which largely represent AR genes we see in the clinic."
That might signal good news that AR genes from cow gut bacteria are not currently causing problems for human patients. But, Wichmann points out, another possibility is that "cow manure harbors an unprecedented reservoir of AR genes" that could be next to move into humans.
"This is just the first in a sequence of studies—starting in the barn, moving to the soil and food on the table and then ending up in the clinic—to find out whether these genes have the potential to move in that direction," says Handelsman.
AR genes can enter the human ecosystem by two routes—either the bacteria that contain them colonize humans, or the genes are transferred through a process called horizontal gene transfer to other bacteria that colonize humans. Research has already shown that bacteria are transferred from farm animals to their human caretakers. Gene transfer enables genes to jump between microorganisms that are not related, and it occurs in most environments that host bacteria.
Some manure bacteria might be pathogenic to humans, so if they acquire antibiotic resistance, they could pose a problem. Alternatively, benign bacteria in manure might transfer resistance genes to pathogens at any point along the path—in manure, soil, food, or humans.
"We're hoping this study will open up a larger field of surveillance, to start looking at new types of resistance before they show up in the clinic," says Handelsman.
The study was funded by the Swiss National Science Foundation and the US National Institutes of Health.
mBio® is an open access online journal published by the American Society for Microbiology to make microbiology research broadly accessible. The focus of the journal is on rapid publication of cutting-edge research spanning the entire spectrum of microbiology and related fields. It can be found online at http://mbio.asm.org.
The American Society for Microbiology is the largest single life science society, composed of over 39,000 scientists and health professionals. ASM's mission is to advance the microbiological sciences as a vehicle for understanding life processes and to apply and communicate this knowledge for the improvement of health and environmental and economic well-being worldwide.
Jim Sliwa | Eurek Alert!
Two decades of training students and experts in tracking infectious disease
27.11.2015 | Hochschule für Angewandte Wissenschaften Hamburg
Increased carbon dioxide enhances plankton growth, opposite of what was expected
27.11.2015 | Bigelow Laboratory for Ocean Sciences
Planet Earth experienced a global climate shift in the late 1980s on an unprecedented scale, fuelled by anthropogenic warming and a volcanic eruption, according to new research published this week.
Scientists say that a major step change, or ‘regime shift’, in the Earth’s biophysical systems, from the upper atmosphere to the depths of the ocean and from...
The Fraunhofer Institute for Solar Energy Systems ISE has installed 70 photovoltaic modules on the outer façade of one of its lab buildings. The modules were...
Nerve cells cover their high energy demand with glucose and lactate. Scientists of the University of Zurich now provide new support for this. They show for the first time in the intact mouse brain evidence for an exchange of lactate between different brain cells. With this study they were able to confirm a 20-year old hypothesis.
In comparison to other organs, the human brain has the highest energy requirements. The supply of energy for nerve cells and the particular role of lactic acid...
In laser material processing, the simulation of processes has made great strides over the past few years. Today, the software can predict relatively well what will happen on the workpiece. Unfortunately, it is also highly complex and requires a lot of computing time. Thanks to clever simplification, experts from Fraunhofer ILT are now able to offer the first-ever simulation software that calculates processes in real time and also runs on tablet computers and smartphones. The fast software enables users to do without expensive experiments and to find optimum process parameters even more effectively.
Before now, the reliable simulation of laser processes was a job for experts. Armed with sophisticated software packages and after many hours on computer...
Researchers at Heidelberg University have devised a new way to study the phenomenon of magnetism. Using ultracold atoms at near absolute zero, they prepared a...
25.11.2015 | Event News
17.11.2015 | Event News
21.10.2015 | Event News
27.11.2015 | Press release
27.11.2015 | Life Sciences
27.11.2015 | Materials Sciences