Down the Food Chain: Humans Passing Antibiotic Resistance to Protected Animals

It appears humans’ love affair with antibiotics is contributing to a larger trickle-down effect on the food chain than once thought.

Scientists know that antibiotic-resistant bacteria—a major concern for human health—can be transmitted from animals to humans, mainly through consumption of livestock treated with antibiotics, but new research from Virginia Tech shows even protected wildlife aren’t immune from humans’ influence on the evolution of deadly bacteria.

After studying the levels of E. coli in banded mongooses in Botswana, researchers discovered humans are passing down antibiotic resistance to wildlife, including in protected areas with limited human contact. The study also found that the mongooses and humans are regularly exchanging microorganisms that increase the potential for transmitting diseases. 

“With few new antibiotics on the horizon, wide-scale antibiotic resistance in wildlife across the environment presents a critical threat to human and animal health,” Virginia Tech associate professor Kathleen Alexander, said in a press release. “As humans and animals exchange microorganisms, the threat of emerging disease also increases.”

Studying Mongoose and Human Interaction Through Poop

Part of a long-term ecological study, the Virginia Tech researchers studied six different troops on mongoose—three in a protected habitat and three living in villages. The animals foraged through garbage for food, as well as searching for insects in human fecal waste, exposing them to the same strains of bacteria as humans. 

Focusing on E. coli, researchers testing fecal samples from humans and mongoose and found that 57 percent of the mongooses had a branch of the bacteria that was resistant to the common antibiotic treatments doxycyline, tetracycline, and streptomycin.

However, researchers were most shocked at the prevalence of multi-drug resistance but not what they expected. 

One troop outside the protected area had the lowest level of multi-drug resistance while a troop from the protected area living near an ecotourism facility had the highest levels. Researchers attributed this to mongoose living in drain fields from septic tanks and ate raw scraps of commercially-produced chicken, a common source of antibiotics that creates resistance.

As mongoose and other animals are part of a delicate ecosystem, the transmission of antibiotic-resistant bacteria in one animal population can affect others, ultimately affecting everyone in the food chain, including the humans at the top, researchers said. 

“These findings reinforce the significance of human impacts to natural environments, even when human numbers are low,” Alexander said. “As we change our natural environments, these modifications can in turn impact our own health.”

Their research was published in the latest issue of the journal EcoHealth.

Antibiotic Resistance: From Animals to Humans and Useless Treatments

Antibiotic resistance is a major concern in humans. Currently, the best antibiotics are useless against some of the evolving strands of bacteria appearing in U.S. hospitals.

Last week, a study published in PLOS Biology stated that in lab experiments aggressive antibiotic treatment actually makes bacteria’s defenses against treatment stronger and bacteria could defend against the most aggressive treatments in as little as one day.

Earlier this year, a study in Demark linked antibiotic use in livestock to a specific strain of methicillin-resistant Staphylococcus aureus (MRSA), a potentially-lethal bacteria that can begin as small as a skin infection, in humans.

Rep. Louise Slaughter (D-N.Y.) said the Denmark study “ends any debate” that antibiotic overuse through prescription and use in livestock. She used the study as fuel to push a bill that would limit the use of antibiotics in humans and farming. The bill, “Preservation of Antibiotics for Medical Treatment Act” (PAMTA), has been sitting before the House Energy & Commerce Committee since it was introduced in March.

The hope for antibiotic treatments could lie in pitting nature against itself by using viruses to combat bacteria. At Rockefeller University labs, researchers identified a weak point in bacterial armor that allows phages, a type of virus, to enter the bacterial cell and kill it without harming tissue around it. The broad-spectrum antibiotic, Epimerox, has been shown to kill MRSA, the bacteria that causes anthrax, and other gram-positive bacteria. The developers hope to begin human trials within two years.

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