Photo by James W. Porter

Research Reveals Human Impact on Florida Reefs

By Laura J. Cole '04 '08MLS

From salmonella to mad cow disease, infectious diseases get their fair share of play in the media—and with good reason. It’s easier to prevent contamination when you know the cause of the problem and, hence, what to avoid.

Armed with this credo, Associate Professor of Biology Kathryn Sutherland led a research team in exploring the source of pathogens. Rather than focus on the transmission of pathogens from plants and animals to humans—a phenomenon known as zoonosis—Sutherland and University of Georgia research collaborators Erin Lipp, associate professor of environmental health science, and James Porter, professor of ecology and marine sciences, examined how human bacteria infects wildlife.

They didn’t have to travel far from the Florida coast to conduct their research. The focus of their study, Caribbean elkhorn coral, is among Florida’s most-common reef building corals and once flourished in the Florida Keys. Listed as protected since 2006 under the United States Endangered Species Act, this type of coral has been damaged by hurricanes and infected with white pox disease.

White pox kills coral. But where does the white pox originate from?

“When we identified Serratia marcescens as the cause of white pox, we could only speculate that human waste was the source of the pathogen because the bacterium is also found in the waste of other animals,” Sutherland says.

To determine a source of the pathogen, the research team collected and analyzed human samples from the wastewater treatment facility in Key West as well as samples from several other animals such as Key deer and seagulls. While Serratia marcescens was found in these other animals, genetic analyses showed that only the strain from human sewage matched the strain found in white pox-diseased corals on the reef.

The final piece of the investigative puzzle was to show that this strain was pathogenic to corals. With funding from Florida’s Mote Marine Laboratory “Protect Our Reefs” grant program, Sutherland and her colleagues inoculated fragments of coral with the strain found in both humans and corals to see if it would cause disease. The experiments were carried out in a laboratory in closed seawater tanks in order to eliminate any risk of infection to wild populations of corals.

“The strain caused disease in elkhorn coral in five days, so we found definitive evidence that humans are a source of the pathogen that causes this devastating disease of corals,” Sutherland said.

In humans, Serratia marcescens causes respiratory, wound, and urinary tract infections; meningitis; and pneumonia. Human diseases caused by this bacterium are most often associated with hospital-acquired infections of newborn infants and immuno-compromised adults. The research proved groundbreaking, as movement of disease-causing microbes from humans to marine invertebrates had not previously been shown.

“This 'reverse zoonosis' is all the more interesting because it involves the jump of a pathogen from vertebrate to invertebrate and from terrestrial to marine,” Porter said.

Sutherland and her research partners identified and verified the source of the infectious disease: human bacteria. Thanks to a $2.2-million grant from the National Science Foundation, they are now investigating other factors that contribute to the emergence and maintenance of white pox outbreaks, including water quality, climate variability, and patterns of human population density.

This information will provide valuable insight into ways to contain—and hopefully reduce—the  bacteria’s contamination of coral, which provides the foundation for a dynamic ecosystem.