Vibrio vulnificus
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| Vibrio vulnificus |
Description and significance
Vibrio vulnificus is a rod-shaped, gram-negative bacterium that ferments lactose. It is a halophile and can be found in warm coastal waters and is very common in the Gulf Coast environments. Vibrio vulnificus grows best in the warm months when the water temperature is between 20 to 24° C and cannot be found in cold water.
It is also motile and like two other bacteria found in the Family Vibrionaceae, Vibrio cholerae and Vibrio parahaemolyticus, is a human pathogen. It is known to cause very serious problems and sometimes death in humans if it is ingested or if it contaminates an open wound in the skin.
Strains of V. vulnificus can be divided in three biotypes; strains virulent for humans are categorized in biotypes 1 and 3 while strains that are virulent for fish are classified as biotype 2. Gene sequencing has allowed for the identification of the virulence genes in V. vulnificus and the ability to better the examination of an infection. It was first described as a pathogen in 1976 by Hollis et al.
Genome structure
The biotype 1 strain of Vibrio vulnificus has two circular chromosomes and a smaller plasmid. The larger of the two chromosomes is 3,354,505 bp long while the smaller chromosome is 1,857,073 bp long. The plasmid identified was of 48,508 bp. A super- integron containing 188 gene cassettes was also identified. These gene cassettes vary greatly for among the different strains and are distinctive for each Vibrio species. Genes that encode for the production of capsular polysaccharide, RTX, toxins, and type IV pilus (all of which play an important role in the virulence of the strain) along with other genes can be found on the chromosome. Multiple rearrangements, gene duplications, and signs of horizontal transfer were also present on the genome.
Cell structure and metabolism
This bacterium can have a flagellum which allows for its motility. It can also have type IV pili which may be a factor of virulence since they help the bacteria attach to the epithelial cells. Some strains of V. vulnificus are capsulated while others are not. The presence of capsular polysaccharide can greatly increase the virulence of the bacteria. Some strains of V. vulnificus are known to ferment lactose while others ferment sucrose.
Ecology
Marine environments and its inhabitants can serve as shelters for V. vulnificus. Organisms that harbor this bacterium include oysters, eels, shellfish and seaweed. When these organisms are consumed either raw or undercooked by humans it can cause great damage to the health of person and sometimes even death.
Pathology
Vibrio vulnificus can cause serious damage to human beings especially since its infectious dose is not known. It can enter the body if one consumes raw or undercooked seafood (especially oysters). In a healthy person, ingesting V. vulnificus can cause gastroenteritis which is characterized by diarrhea, vomiting, and stomach aches. Sepsis, ulceration, and necrotizing faciitis among other things are also common if an open wound is infected.
In a person who already has a disease that compromises his/her immune system (such as liver disease, cancer, HIV, etc) the consequences of infection by this bacterium are far more severe. V. vulnificus can cause primary septicemia or bloodstream infections which can then lead to high fevers, septic shock and death. There is a fifty percent chance of fatality in immunocompromised persons.
There are a number of enzymes produced by the bacterium that assist in the infection. Some of these enzymes are lipase, DNAase, and mucinase. The presence of polysaccharide capsules, lipopolysaccharide (LPS), RTX toxins and type IV pili (which allow the bacterium to attach to the epithelial cells) allow for a stain to be virulent. People with Vibrio vulnificus infections are treated antimicrobial agents. Some antibiotics that work the most effectively are tetracycline, aminoglycosides, and third- generation cephalosporins.
Application to Biotechnology
This organism does not produce any enzymes that prove beneficial to humans. It does, however, produce endotoxins and enzymes that could increase its virulence. These enzymes and toxins include RTX toxins, lipopolysaccharides, lipases, and proteases among others.
Current Research
Vibrio vulnificus Damages Macrophages during the Early Phase of Infection.
Not much is known about the mechanisms through which V. vulnificus causes disease. The pathogenicities of a clinical isolate and of an environmental isolate were tested during this research. The clinical isolate, strain M2799, was described a hundred times more lethal in mice than strain JCM3731, which is the environmental isolate. Even though there are a number of virulence factors, the expression of capsular polysaccharide (CPS) is related to the fatality in animal models. Strains of V. vulnificus that are encapsulated are much more lethal than strains that are not. This is because the capsular polysaccharide serves to protect the strain from undergoing phagocytosis by macrophages and neutrophils. Studies have shown that lymphocytes in the host are lost through apoptosis induced by V.vulnificus. Through this research it is shown that the clinical strain was very effective in inducing apoptosis in macrophage while the environmental strain was not able to. There was a high level of cytotoxin activity in strain M2799 which then led to a decrease in the number of macrophages. In strain JCM3731, the cytotoxin level was about thousand fold lower and the macrophages were not affected. The effect of macrophages and neutrophils on the growth of V. vulnificus was also examined in this research. Results show that macrophage function to completely inhibit the growth of strain M2799 and that neutrophils are half as effective in inhibiting the growth of this strain. These results show that macrophages are critical in stopping an infection caused by V. vulnificus and that neutrophils alone cannot prevent the infection but rather only help the macrophage in inhibiting the growth of this bacterium.
Necrotizing Fasciitis from Vibrio vulnificus in a Patient with Undiagnosed Hepatitis and Cirrhosis
References
[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1951150 Tsuchiya, T., Mitsuo, E., Hayashi, N., Hikita, Y., Nakao, H., Yamamoto, S., Miyamoto, K., and Tsujibo, H. "Vibrio vulnificus Damages Macrophages during the Early Phase of Infection". "Infection and Immunity".2007.]