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Microbes becoming resistant to pharmaceutical pollution

Pharmaceutical pollution in urban streams can cause aquatic microbial communities to become resistant to drugs, according to a new study. The researchers set out to determine what this means for water quality and ecological function.

Emma Rosi is an aquatic ecologist at the Cary Institute of Ecosystem Studies and lead author of the study.

“Wastewater treatment facilities are not equipped to remove many pharmaceutical compounds,” said Rosi. “We were interested in how stream microorganisms – which perform key ecosystem services like removing nutrients and breaking down leaf litter – respond to pharmaceutical pollution.”

The research team selected four streams in Baltimore, Maryland, which ranged from urban to suburban. They tested for the presence of painkillers, stimulants, antihistamines, and antibiotics.

Microorganisms like bacteria and algae are key in maintaining freshwater health. They break down contaminants, promote nutrient cycling, and form the base of the stream’s food web.

“Different types of microbes can withstand different types and concentrations of synthetic chemicals,” said Rosi. “When we expose streams to pharmaceutical pollution, we are unwittingly altering their microbial communities.”

The study revealed that urban streams had a higher number of drugs present in higher concentrations compared to suburban streams.

The researchers also developed a test which singled out the drugs and examined how microbial communities responded to each in terms of survival and function.

“Stream microbial communities are sensitive to pharmaceuticals, which can suppress both respiration and primary production,” said co-author John J. Kelly. “We used respiration as a proxy to assess microbes’ ability to maintain biological function in the presence of pharmaceuticals.”

Caffeine, cimetidine, and ciprofloxacin were found to cause a reduction in microbial respiration across all sites, while diphenhydramine was found to have a marginal effect. The antibiotic ciprofloxacin had a negative effect on respiration rates, but only in suburban streams.

The experts noted that the type and density of microbial species were different at urban and suburban sites after drug exposure. In urban streams, microbial communities transformed in composition and were better able to maintain respiration rates, suggesting that these streams harbor resistant microbes that manage to thrive where non-resistant species cannot survive.

“We suspect that since urban streams have received frequent pharmaceutical inputs over long timescales, pockets of drug-resistant microbes have developed in these streams,” said Rosi. “They are ready to colonize substrates, even when drugs are present. When faced with pharmaceutical exposure, these resistant microbes can maintain ecological function, even when other species have been eliminated.”

The study is published in the journal Ecosphere.

By Chrissy Sexton, Staff Writer

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