Removing fear from oysters
wonders of nature's waters - oysters. Unfortunately, for a handful
of people each year the pleasure can be disastrous if they become
infected by a deadly bacteria associated with the bivalves. But new
research released this week suggests that there may be a cure.
This week people across the world will be indulging in one of the wonders of nature's waters - oysters. Unfortunately, for a handful of people each year the pleasure can be disastrous if they become infected by a deadly bacteria associated with the bivalves. But new research released this week suggests that there may be a cure.
Two University of Florida researchers report curing mice of the disease by using a virus to attack its bacterial source - Vibrio vulnificus. The scientists report that the research may lead to techniques to purify oysters after harvest but before they reach raw bars and seafood markets - and might one day result in a better cure for the disease in people.
The work, reported in a recent issue of the journal Infection and Immunity, is part of a growing trend in research to use bacteria-attacking viruses, or "phages," to cure diseases caused by bacteria, said Paul Gulig, a UF professor of molecular genetics and microbiology at UF's College of Medicine.
Although the disease caused by Vibrio responds to antibiotic treatment if caught early enough, the trend toward research of phages is spurred in part by the increasing ineffectiveness of antibiotics in killing ever-more-resistant bacteria, he claims.
"Phages haven't been used in the United States since the early 20th century because antibiotics have worked pretty well," said Gulig. "That's changing now, and there is more interest in investigating the phage alternative."
Vibrio vulnificus is related to the cholera bacterium and occurs naturally in the presence of microscopic algae in seawater. When oysters eat the algae, Vibrio becomes concentrated. People can come into contact with the bacterium by eating raw oysters (cooking the bivalves kills the bacterium), or by exposing an open wound to water or mud where the bacterium is present.
Most exposed people suffer no ill effects because their bodies easily fight off the bacterium. However, people who suffer from liver damage - from alcohol-related cirrhosis, for example - may become infected. Although rare, the disease is severe and often fatal, killing between 50 per cent and 75 per cent of those who are infected. The bacterium causes flu-like symptoms, followed by high fever, shock and half-dollar sized blood blisters mostly on the patient's legs.
Gulig and Donna Duckworth, a professor of molecular genetics and microbiology and co-author of the article, said because Vibrio resembles the flu or less-harmful diseases, it often remains undiagnosed until its later stages. At that point, the disease does not respond well to antibiotics, hence its high mortality rate, they said. Seeking an alternative to antibiotics, he and Duckworth decided to test the effectiveness of phages in attacking the disease.
The scientists isolated phages that prey naturally on the bacterium from oysters purchased from seafood markets and in mud collected from oyster beds in Florida's coastal waters. They grew the phages in the laboratory, then injected solutions containing concentrated amounts of the virus into the tail veins of mice infected with Vibrio. As to the results, researchers found the phages cured the mice even well after they had begun experiencing symptoms of the disease.
"It was very clear that the phage treatment for many of the mice could completely protect them. It could prevent death, and it could essentially clear the mice of bacteria," Gulig said. "We showed that, in typical infections of mice, we get 100 million bacteria per gramme of tissue, and in these treated mice we essentially could not detect any bacteria at all."
Gulig said the project did not compare the phages with similarly timed antibiotic treatments, so the researchers could not say which is more effective. But phages have some tantalising advantages over antibiotics, he said.
While antibiotics naturally become diluted and leave the body after a period of time, phages grow and multiply until they have preyed on all the available bacteria, he added. Also, antibiotics are general treatments, killing harmful bacteria as well beneficial organisms, making patients vulnerable to yeast infections and other maladies. Phages, by contrast, are extremely specific, with the virus seeking only its natural prey and thus causing no unexpected outcomes.
Alexander Sulakvelidze, an assistant professor of microbiology and epidemiology at the University of Maryland, said the new method appears promising.
The research, funded with a $64,000 grant from the US Department of Commerce SeaGrant Programme, is set to pursue a new direction: using phages to purify oysters before they reach consumers. The idea would be to submerge the harvested oysters in vats of phage-treated water, allowing them to filter in the phage and kill off the Vibrio vulnificus before the oysters reach the market.
Gulig claims that such technology would be quicker and cheaper to develop and commercialise than a new treatment for Vibrio disease, because it would not have to meet regulatory standards for human medicine. "It would be a truly natural treatment, since we're essentially treating the oysters with something they're already exposed to in the wild," concluded Gulig.
