Research in Florida finds 88% of samples have pathogen that resists at least one antibiotic

Antibiotic resistance is rising in dolphins, researchers have said, mirroring the trend seen in humans.

Scientists examined disease-causing organisms, or pathogens, found in samples from the blowholes, gastric fluid and faeces of bottlenose dolphins from the Indian River Lagoon in Florida. The samples were collected between 2003 and 2015.

The area has a large human population on the coast and significant environmental problems. “They include septic tanks, runoff from the land, freshwater discharge from canals, to name a few,” said Adam Schaefer of Florida Atlantic University, the study’s lead author.

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Of the 733 samples from 171 dolphins analysed, 88% contained a pathogen resistant to at least one antibiotic. The antibiotic to which the pathogens were most commonly resistant was erythromycin, which is commonly used to treat chest infections, acne and sexually transmitted infections including chlamydia and syphilis.

Resistance to the antibiotic ciprofloxacin among E coli pathogens more than doubled over the period studied, mirroring trends in human infections.

“Antibiotic resistance is one of the most significant risks to public health,” said Gregory Bossart, the chief veterinary officer at Georgia Aquarium and a co-author of the study. “As resistance increases, the probability of successfully treating infections caused by common pathogens decreases.” At least 2 million people get an antibiotic-resistant infection in the US each year, and at least 23,000 people die as a result.

“In 2009, we reported a high prevalence of antibiotic resistance in wild dolphins, which was unexpected,” Schaefer said. “Since then, we have been tracking changes over time and have found a significant increase in antibiotic resistance in isolates from these animals.

“This trend mirrors reports from human healthcare settings. Based on our findings, it is likely that these isolates from dolphins originated from a source where antibiotics were regularly used.”

Schaefer said the resistant bacteria enter the lagoon from terrestrial sources including sewage discharge. “Once in the lagoon, the antibiotics create selective pressure on the normal bacteria that are present.

“The bacteria that are not resistant die, and resistant bacteria remain and proliferate, essentially creating a population of resistant pathogens that dolphins are exposed to.”

The study was published in the journal Aquatic Mammals.