A recent study unearthed a threat that could add to the growing concern about antibiotic resistance in today's modern medicine. It turns out that a seemingly innocuous mound of cow manure is harboring a number of newly identified genes that can beef up any pathogen's resistance to antibiotics.
The findings published in mBio, the online open-access journal of the American Society for Microbiology, revealed that the genes, which originated from bacteria present in the cows' gut, could latch onto the microbes in the soil where crops are cultivated and might seep into the human ecosystem.
In an experiment that employed a "powerful screening-plus-sequencing approach," scientists at Yale University discovered 80 unique antibiotic resistance (AR) genes after sampling manure from cows at a farm in Connecticut.
The genes were then tested to a strain of Escherichia coli (E. coli) bacteria, which presented surprising results. The E. coli became immune to antibiotics such as penicillin, aminoglycosides, tetracycline and chloramphenicol. E. coli carried in food can cause bloody diarrhea and can sometimes cause kidney failure and death.
"The diversity of genes we found is remarkable in itself considering the small set of five manure samples," said senior study author and Yale microbiologist Jo Handelsman in a press release. "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."
Over a thousand known AR genes proved risk-free if they appeared in harmless bacteria. In the study, 75 percent of the 80 AR genes were found to be distantly related to AR genes already discovered. But what if these genes get into the ones that cause food-borne illnesses or hospital infections? That's where the problem begins.
Scientists are considering the possibility that food produced from soils fertilized with cow manure could transport bacteria with the genes from the farm to humans through human consumption.
"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," Handelsman said.
According to an article by the Alliance for the Prudent Use of Antibiotics, bacteria's resistance to antibiotics can be triggered by genetic mutation or by acquiring resistance from another bacterium.
"The increasing prevalence of antibiotic resistance among bacteria is one of the most intractable challenges in 21st-century public health," former Yale postdoctoral researcher Fabienne Wichmann, lead author of the study, concluded.
The study was funded by the Swiss National Science Foundation and the National Institutes of Health in the United States.
