August 18, 2011
Photo by James W. Porter (University of Georgia)
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 (UGA) 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? Initially, they only had a hunch that it was from humans.
“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.
In order to determine a source for 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 unique 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 marcesccens 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 researched 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 (NSF), 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 the ways to contain and hopefully reduce the harmful bacteria from contaminating coral, which provide the foundation for a dynamic ecosystem.
Read their published study in the journal PLoS One. A coauthor of the paper, Sameera Shaban (Class of 2010) traveled to the Keys and spent her senior year playing a key role in the research as part of the 2009 Student-Faculty Collaborative Scholarship Program and her honors senior research project.
Listen to the story on NPR.
By Laura J. Cole
This summer, Hunter Noren (Class of 2012) got the chance to join Sutherland’s research team as part of the Student-Faculty Collaborative Scholarship program. Sutherland, Noren and nine other researchers on the team stayed at the Mote Marine Lab on Summerland Key and participated in research-based diving expeditions on a nearby coral reef.
The purpose of the May/June 2011 trip was to study the microbial community on coral when it is in a non-diseased state. “This trip was about collecting baseline date,” said Sutherland, who worked with Noren to collect samples of the mucus on the coral.
Unlike previous student collaborators Sutherland has partnered with for summer research, Noren is a certified dive master, the first student researcher she’s worked with who holds that credential. “Hunter has been diving since he was 13 years old,” said Sutherland. With more than 200 dives under his belt, Noren has a high comfort level in the water, which proved tremendously helpful.
Nearly every day, the research team headed out to the reef to collect samples they later filtered and processed in the lab. Noren was thrilled with the hands-on experience. “It showed me not just the lab aspect but also the field aspect, which was pretty great.”
As part of her NSF grant, Sutherland has funding for undergraduate students to go with her to the Keys every year of the five-year research project. “These funds pay for their stipend as well as all the travel expenses to the Keys, allowing these students to be active participants in the project,” shared Sutherland.
Watch a dive expedition that Sutherland and Noren took as part of their research.
By Kristen Manieri
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