Abstract

South Florida and its coastal regions are under increasing environmental stress due to the vast population growth and coastal development. The Indian River Lagoon (IRL) comprises 40% of the Florida's east coast and therefore, this ecosystem is susceptible to environmental stress and pollution. Of particular concern is sewage outfall which has been found to harbor antibiotic resistant E. coli during and after sewage treatment.³ Previous microbiological studies in the IRL have identified E. coli harboring resistance to antibiotics commonly used in human and veterinary medicine, aquaculture and agriculture in the free ranging dolphin population.^1,4 To our knowledge, the current study is the first attempt to examine the occurrence of antimicrobial E. coli in IRL dolphins using a spatial and temporal approach to identify particular areas of risk. The areas bordering the IRL vary in population size, particularly between areas of higher agricultural land use and urban development. Therefore, the potential for exposure to antimicrobial resistant bacteria differs throughout the lagoon. The purpose of this study was to incorporate dolphin spatial distribution data with biological and environmental characteristics to identify risk factors for colonization of antibiotic resistant E. coli in dolphins in the IRL.

Animal sex, weight, capture site, age, year of capture, surrounding human population density, and sewage discharge sites were included in the analysis. The IRL was divided into 6 segments based on hydrodynamics and geographic features and dolphins were assigned to each segment on the basis of their sighting histories from photo-identification studies and HERA capture site.² Fecal cultures from 96 dolphins examined between 2003 and 2007 as a part of the dolphin health and risk assessment project (HERA) were included in the study. A total of 34 positive E. coli cultures, 67% resistant to one or more antibiotic cultures were grown. Animals sampled from the northernmost region of the lagoon were 4.3 (95% CI 0.97, 19.4) times more likely to have a positive culture as compared to the southernmost segment. In contrast, two segments exhibited a statistically significant reduced risk (OR = 0.08 [95% C.I. 0.01 - 0.59] and 0.07 [95% C.I. 0.01, 0.49]) when compared to the northernmost segment of the lagoon. In addition to segment, year of capture was a significant risk factor for colonization. Temporally, animals cultured in 2004 and 2005 were 18.0 (95% C.I. 3.52, 91.9) and 7.7 (95% 1.35, 43.9) times more likely respectively to be positive for E. coli compared to 2003. Biological measures of age, weight, and sex were not significant risk factors for antibiotic resistance. The role of environmental risk factors and specific sources of coliform introduction is still uncertain and additional study is currently underway. The incorporation of spatial and temporal data in the study of antibiotic resistant bacteria in the IRL was a useful first step in identifying potential environmental hazards and provides direction for further analysis.

Acknowledgments

This work was conducted under NMFS permit 998-1678 issued to Dr. Gregory Bossart as part of the Health and Risk Assessment of Bottlenose Dolphins Project (HERA) conducted in the Indian River Lagoon, FL and the coastal waters of Charleston, SC. Special thanks tothe numerous collaborators and volunteers who participated in making the HERA project a success.

References

1.  Greig T.W., J.A. Bemiss, B.R. Lyon, G.D. Bossart, and P.A. Fair. 2007. Prevalence and diversity of antibiotic resistant Escherichia coli in bottlenose dolphins (Tursiops truncatus) from the Indian River Lagoon, Florida, and Charleston Harbor area, South Carolina. Aquatic Mammals 33: 185-194.

2.  Mazzoil M., S.D. McCulloch, M.E. Murdoch, S.E. Bechdel, E. Howells, M. Youngbluth, L.J. Hansen, J.S. Reif, and G.D. Bossart. 2008. Bottlenose dolphin (Tursiops truncatus) home range patterns and environmental characterization in the Indian River Lagoon System, Florida. EcoHealth. Published online October, 2008 DOI: 10.1007/s10393-008-0194-9.

3.  Reinthaler F.F., J. Posch,, G. Feierl, G. Wust, D. Haas, G. Ruckenbauer, F. Mascher, and E. Marth. 2003. Antibiotic resistance of E. coli in sewage and sludge. Water Research 37: 1685-1690.

4.  Schaefer A.M., J.D. Goldstein, J.S. Reif, P.A. Fair, and G.D. Bossart. 2009. Antibiotic resistant organisms cultured from Atlantic bottlenose dolphins (Tursiops truncatus) inhabiting estuarine waters of Charleston, SC and the Indian River Lagoon, FL. Eco Health, in press.