Antibiotic resistance is one of the biggest public health challenges in the world today as many common bacterial infections are developing resistance to drugs once used to treat them and new antibiotics have not been developed fast enough to combat the problem.
Once limited mainly to health facilities, these resistant strains of bacteria are now commonly found in other places, particularly marine environments. To date, few studies have examined the long-term trends of antibiotic resistance in pathogens isolated from wild animal populations.
Researchers at the Harbor Branch Oceanographic Institute of Florida Atlantic University in collaboration with Georgia Aquarium, Medical University of South Carolina and Colorado State University, conducted a unique long-term study (2003-2015) on antibiotic resistance among isolated pathogens from the bottlenose dolphins (Tursiops truncatus) in the Indian lagoon of the Florida river. This lagoon has a large human coastal population and significant environmental impacts.
"In 2009, we reported a high prevalence of antibiotic resistance in wild dolphins, which was unexpected," said Adam M. Schaefer, MPH, lead author and epidemiologist at the FAU Harbor Branch. "Since then, we have followed the changes over time and found a significant increase in antibiotic resistance in the isolates of these animals. This trend reflects the reports of human health care settings. Based on our findings, it is likely that these isolates from the Dolphins originate from a source where antibiotics are regularly used, potentially entering the marine environment through human activities or discharges from land-based sources. "
Using 13 years of data and the index of resistance to multiple antibiotics (MAR), the researchers obtained a total of 733 pathogen isolates from 171 single bottlenose dolphins. Many of the organisms isolated from these animals are important human pathogens.
Results of the study, published in the journal Aquatic mammals, shows that the overall prevalence of resistance to at least one antibiotic for the 733 isolates was 88.2%. The prevalence of resistance was highest at erythromycin (91.6 percent), followed by ampicillin (77.3 percent) and cephalothin (61.7 percent). This is one of the few studies to use the MAR index for bacterial isolates of a marine mammal species.
Ciprofloxacin resistance among E. coli isolates more than doubled between sampling periods, reflecting recent trends in clinical infections in humans. Pseudomonas aeruginosa, responsible for infections of the respiratory system, urinary tract infections, among others, were the highest recorded for any organism and increased during the study period.
The MAR index increased significantly between the periods 2003-2007 and 2010-2015 for P. aeruginosa and Vibrio alginolyticus, a common pathogenic species of Vibrio marina that found serious seafood poisonings. For all bacterial isolates, resistance to cefotaxime, ceftazidime, and gentamicin increased significantly between the sampling periods.
"The risk assessment for health and the environment or the HERA project have helped to discover that the emerging bacterial resistance to antibiotics in bottlenose dolphins is prevalent. The bottlenose dolphins are a valuable sentinel species that helps us understand how this affects human and environmental health. Through HERA we were able to provide a large database of information in order to continue learning from these impressive animals, "said Gregory D. Bossart, VMD, Ph.D., co-author, senior vice president and veterinary chief at Georgia Aquarium. "Antibiotic resistance is one of the most significant risks to public health. Increasing resistance decreases the likelihood of successfully treating infections caused by common pathogens."
The sampling for the study was conducted and funded in part by the Florida License Plate Fund and the Georgia Aquarium, with Bossart at the head of HERA and the permit holder. Microbiology swab specimens were taken from the breather, gastric fluid and faeces and grown on standard media under aerobic conditions. The most frequently isolated pathogens were Aeromonas hydrophila, E. coli, Edwardsiella tarda, V. alginolyticus and S. aureus, pathogens often associated with aquatic environments. Dolphins have been captured and released into the Indian River Lagoon as part of the HERA Project. Sampling took place in June and July of each year.
"The national impact on human health of the pathogen Acinetobacter baumannii is of great concern as it is an important nosocomial pathogen with an increase in infection rates in the last 10 years," said Peter McCarthy, Ph .D., Co-author, research professor and an associate director for education at the FAU's Harbor Branch. “In addition to nosocomial infections, resistant strains associated with fish farming have been reported globally. The high MAR index for this bacterium isolated from dolphins in the Indian River Lagoon represents a major public health concern. "
Every year in the United States, at least 2 million people receive an antibiotic resistant infection and at least 23,000 people die.
Co-authors of the study are Tyler Harrington, FAU's Harbor Branch; Patricia A. Fair, Ph.D., Medical University of South Carolina; and John S. Reif, Ph.D., Colorado State University.
This work was funded in part by the Protect Wild Dolphin license funds granted through the Harbor Branch Oceanographic Institute Foundation and the Georgia Aquarium.