Field Note 



Stalking a Dangerous Bacteria 



When Jim Oliver has a bushel of oysters delivered to his 

 Charlotte address, his mind isn't on eating the delectable mollusks. 

 Far from it. 



These oysters are destined for intense probing in a university 

 laboratory as this Sea Grant researcher tries to unravel the 

 mysterious behavior of a deadly bacteria sometimes carried by the 

 mollusks. 



The bacteria, vibrio vulnificus, can be deadly for people who 

 suffer from liver ailments or immune deficiency diseases if they eat 

 infected oysters raw or partially steamed. Properly cooked, the 

 infected oysters pose no threat even to people with underlying 

 illnesses, says David Green, Sea Grant's seafood technology 

 specialist. 



Even healthy individuals should consider cooking their 

 shellfish to an internal temperature of 160 F, Green says. Con- 

 sumption of any raw meat or seafood can pose some health risks. 



Vibrio vulnificus is part of a larger family of bacteria known 

 simply as vibrio. Thirty species of vibrio have been counted, and 

 10 are known human pathogens, Oliver says. 



These species of vibrio that affect humans act as gastrointesti- 

 nal pathogens that cause food-poisoning symptoms — cramps, 

 diarrhea and vomiting. Vibrio choleme is responsible for the recent 

 outbreak of cholera in South America. 



Not all oysters carry vibrio vulnificus, although the bacteria is 

 a common pathogen found in estuarine and ocean waters along 

 the Atlantic, Gulf and Pacific coasts. But even those shellfish 

 contaminated with the bacteria are not always infectious. 



It's all of these ifs, ands and buts about vibrio vulnificus that 

 has researchers such as Oliver at the University of North Carolina 

 at Charlotte and Sea Grant scientist Gary Rodrick at the University 

 of Florida trying to find some answers. 



So far, most of the illnesses and deaths resulting from this 

 bacteria have been traced to oysters harvested from waters warmer 

 than 68 F. And people can contract the bacteria directly from the 

 water through open wounds. 



It affects mostly men over 40 years old who have a pre- 

 existing disease, commonly cirrhosis of the liver. 



Unfortunately, when vibrio vulnificus strikes, it strikes fast. 



The onset of symptoms — fever, chills, nausea, vomiting and 

 secondary lesions — can begin in as little as seven hours after 

 consumption of contaminated shellfish, Oliver says. And it is not 

 uncommon for patients to die two to four hours after admission to 

 a hospital. 



But if diagnosed quickly, victims are treatable, Green says. 

 The good news is that reports of vibrio vulnificus infections 



Insights into Current Sea Grant Research 



are not common — only one per 200,000 people per year. 



And Oliver would like to make them even rarer, better still, 

 nonexistent. 



He has been examining ways to rid contaminated oysters of 

 this potentially deadly pathogen. 



It was once thought the disease was more prevalent in oysters 

 that were transported for long distances and sometimes allowed to 

 get too warm. But Oliver's recent Sea Grant studies proved that 

 temperature did not affect the growth of this bacteria in shellfish. 



Also, scientists believed that the threat of this vibrio could be 

 reduced through depuration. This means that oysters would be 

 placed in clean water void of the bacteria and allowed to purge 

 themselves. 



Depuration worked for oysters that were infected with the 

 bacteria in the laboratory, Oliver says. But it didn't faze oysters that 

 were contaminated naturally. 



Despite this grim news, Oliver says that there is new hope in 

 the discovery of two strains of vibrio vulnificus. One strain is 

 infectious; the other is not. 



Oliver and other scientists are now looking for the genetic 

 switch that would allow them to convert the infectious strain of 

 this vibrio to the non-infectious form. 



But for now, for those at risk, the only sure way to eat oysters 

 is to have them well-cooked. 



Meanwhile, the Food and Drug Administration and other 

 seafood experts are doing their best to warn those who are 

 susceptible while allaying the fears of those who aren't. 



Kathy Hart 



COASTWATCH 17 



