Why are Florida’s dolphins becoming resistant to antibiotics?

Drug resistance is spreading to marine wildlife, and the dangers to both animals and humans are real

January 24, 2020
An image of some bottlenose dolphins with some artificial construction in the background
Overuse of antibiotics has put bottlenose dolphins at risk. [Alexandre Roux, flickr | Creative Commons]

When Adam Schaefer’s team began examining bottlenose dolphins in the Indian River Lagoon on Florida’s Atlantic Coast over a decade ago, they weren’t searching for any particular health problem. But the more blowholes they swabbed, and the more stomachs and feces they tested, Schaefer’s team slowly stumbled upon something alarming: a pattern of antibiotic-resistant bacteria.

“We certainly became a lot more interested [in antibiotic resistance] after the first few years,” says Schaefer, who studies animal diseases at the Harbor Branch Oceanographic Institute of Florida Atlantic University.

A startling 88% of the swab samples Schaefer’s team collected from those dolphins between 2003 and 2015 were resistant to at least one antibiotic. Even more alarming to Schaefer, his team found that the rates of resistance to two of the most common bacteria –– P. aeruginosa, which can fatally infect organs, and V. alginolyticus, which can cause ear, eye and wound infections –– were drastically higher in 2010-2015 than in 2003-2007.

The rise leaves dolphins vulnerable to the same risks from antibiotic-resistant “superbugs” that are increasingly threatening many kinds of organisms, including humans. Over two million people catch antibiotic-resistant infections annually in just the United States, causing at least 23,000 deaths every year, according to U.S. Centers for Disease Control and Prevention estimates.

What’s affecting the Indian River Lagoon’s dolphins “is the same pattern you see in hospitals,” says Schaefer. His team published their findings in September in the journal Aquatic Mammals. 

“The findings reported here are unfortunately becoming more commonplace,” says Ben Swift, an antimicrobial resistance researcher at the Royal Veterinary College in London. Swift wasn’t involved in Schaefer’s study.

It’s a recurring story in place after place around the globe, from seals and porpoises in the Pacific Northwest to iguanas in the Galápagos to sea lions in Australia to birds, rodents, and bats in Kenya.

Antibiotic resistance originates in nature. Most antibiotics are derived in the first place from microorganisms, who evolved them as a leg up over competing species. Penicillin, for instance, originated in certain species of mold as a way to block the growth of bacteria and give those molds an edge when it came to food sources. In turn, antibiotic resistance evolved naturally as a counter-defense. But nature doesn’t account for the sheer amount of antibiotics that humans –– and Floridians –– use.

In the United States alone providers wrote over 270 million antibiotic prescriptions in 2015, one in three of which were inappropriate or unnecessary. Some antibiotic-resistant pathogens in dolphins may come from direct human contact. But the more likely source is antibiotics, often flushed down toilets, which wind up in sewers and septic tanks –– and eventually into rivers and seas, since conventional wastewater treatment doesn’t catch them.

Another major culprit is agriculture, which heavily uses antibiotics in the name of protecting crops and livestock from disease. In 2016, over 18 million pounds of antibiotics were sold for use in American agriculture. Florida is one of the largest contributors; it has nearly 10 million acres of farmland, according to the U.S. Department of Agriculture, and earlier this year, the U.S. Environmental Protection Agency approved the large-scale spraying of antibiotics in Florida to help combat citrus greening, a fast-spreading bacterial disease that devastates orange groves. These antibiotics, too, can end up in the water.

The Indian River Lagoon, along Florida’s east coast, is especially vulnerable since it’s the drainage basin for both artificial canals and natural bodies of water as far inland as Lake Okeechobee. That means wastewater can flow into the lagoon from across a wide swath of Florida.

When all those antibiotics enter a bacterial environment, they begin attacking non-resistant bacteria en masse, suddenly putting antibiotic-resistant “superbugs” at an advantage. “You are putting on a strong ‘driver’ which is selective for more resistance,” says Swift. These “superbugs” can then multiply and spread quickly and spread through their environment.

Both Swift and Schaefer agree that antibiotic resistance is a global threat that imminently needs to be addressed. That means, to start, reducing wastewater, only using antibiotics when necessary, and disposing of antibiotics properly in a sealed container or by returning it to a pharmacy –– not flushing them down the toilet.

What’s happening to Indian River Lagoon’s dolphins, adds Schaefer, “is ultimately a reflection of the health of the ecosystem.”

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