September 30, 2023

Yes, flesh-eating bacteria can hitch a ride on seaweed and plastic (no, don’t cancel your summer vacation)

Disease-causing bacteria, including the type behind flesh-eating infections, can colonize rafts of seaweed and plastic pollution in the ocean, raising concerns about the risks to humans if they wash up on beaches. But experts say there’s no need to cancel your beach vacation just yet.

A recent study, published last month in the journal Water Research, analyzed the genomes of vibration bacteria — of which there are more than 100 species, including a dozen that can cause human disease — found on plastic marine debris and giant blooms of seaweed called sargassum in the North Atlantic. That’s what the scientists thought vibration bacteria found in the open ocean have similar genetic characteristics to vibration species known to be “pathogenic,” meaning they can cause disease in humans.

The findings fueled fears that flesh-eating bacteria are invading beaches in Florida, the Caribbean and elsewhere in the Gulf of Mexico, where thick mats of sargassum have washed up.

Linda Amaral-Zettler, a marine microbiologist at the Royal Netherlands Institute for Sea Research and one of the authors of the recent study, said that while they may share some genetic ingredients, not all vibration bacteria are pathogens.

“I don’t think everyone should run from sargassum like it’s going to kill them,” she said. “That’s just not the case. But I think we need to think responsibly about the potential risks.”

People can become infected by vibration species from eating raw or undercooked shellfish, or through open wounds. The most dangerous species Vibrio vulnificuscauses carnivorous disease, but these infections are considered rare.

A separate study, published in March in the journal Scientific Reports, found that infections caused by Vibrio vulnificus along the U.S. East Coast could increase significantly in the coming decades as climate change and warmer sea surface temperatures allow the flesh-eating bacteria to thrive in waters farther north than ever before. Scientists have been sounding the alarm over a prolonged heat wave in the ocean in recent months, as sea surface temperatures have reached record-breaking highs and could become warmer.

Both research papers highlight the tangled relationships between humans, microbes and marine ecosystems – and the potential risks to public health that could increase with shifts in the marine environment.

Massive mounds of sargassum have already caused headaches in parts of Mexico and South Florida this year. The thick mats of algae can destroy coral habitats and reduce water and air quality if they wash up and rot on beaches.

“All of these things are very important and could shape how we determine whether our beaches are safe in the future,” said Amaral-Zettler.

Rachel Diner, a marine biologist who was not involved in any of the recent studies, said the number is deadly vibration infections are still relatively low, cases are likely to increase due to climate change. As a postdoctoral researcher at the University of California, San Diego, Diner studied how coastal microbes are affected by changes in their environment.

Vibrios like hot water, so infections through Vibrios have increased in recent decades and so has the vibration concentrations themselves,” she said. “It’s pretty reasonable to expect to see more infections and more of these pathogenic species in the future.”

Diner, who will become an assistant professor in the Department of Biological Sciences at the University of Memphis later this summer, said it’s not entirely surprising to discover vibration bacteria hitch a ride on seaweed blooms and plastic pollution in the ocean.

“They attach to things and live on different surfaces,” she said. “It’s not entirely clear how common that is or how dangerous that is, but that’s sort of an active area of ​​research right now.”

For Amaral-Zettler, the findings are a reminder of how much humans have changed the marine environment, even in remote places far from land.

“We were in the middle of nowhere in the Atlantic and saw huge rafts of sargassum with visible debris in the middle of it,” she said. “That’s hard to look at and realize that in the middle of what we think is a pristine ocean, we’re having an impact and it shows.”

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