Vibrio

Vibrio is a genus of Gram-negative bacteria, which have a characteristic curved-rod shape, several species of which can cause foodborne infection or soft-tissue infection called Vibriosis. Infection is commonly associated with eating undercooked seafood. Being highly salt tolerant and unable to survive in freshwater, Vibrio spp. are commonly found in various salt water environments. Vibrio spp. are facultative anaerobes that test positive for oxidase and do not form spores. All members of the genus are motile. They are able to have polar or lateral flagellum with or without sheaths. Vibrio species typically possess two chromosomes, which is unusual for bacteria. Each chromosome has a distinct and independent origin of replication, and are conserved together over time in the genus. Recent phylogenies have been constructed based on a suite of genes.
O. F. Müller described eight species of the genus Vibrio, three of which were spirilliforms. Some of the other species are today assigned to eukaryote taxa, e.g., to the euglenoid Peranema or to the diatom Bacillaria. However, Vibrio Müller, 1773 became regarded as the name of a zoological genus, and the name of the bacterial genus became Vibrio Pacini, 1854. Filippo Pacini isolated micro-organisms he called "vibrions" from cholera patients in 1854, because of their motility. In Latin "vibrio" means "to quiver".

Biochemical characteristics of ''Vibrio'' spp.

The genus Vibrio contains a large number of species, and these vary somewhat in their biochemical characteristics. Colony, morphological, physiological, and biochemical characteristics of the genus Vibrio are shown in the Table below.

Test type	Test	Group-1	Group-2
Colony characters	Size	Medium	Medium
Colony characters	Type	Round	Round
Colony characters	Color	Whitish	Whitish
Colony characters	Shape	Convex	Convex
Morphological characters	Shape	Curved-rod	Curved-rod
Physiological characters	Motility	+	+
Physiological characters	Growth at 6.5% NaCl	+	+
Biochemical characters	Gram's staining	–	–
Biochemical characters	Oxidase	+	+
Biochemical characters	Catalase	+	+
Biochemical characters	Oxidative-Fermentative	Fermentative	Oxidative
Biochemical characters	Motility	+	+
Biochemical characters	Methyl Red	+	–
Biochemical characters	Voges-Proskauer	+	–
Biochemical characters	Indole	–	–
Biochemical characters	H₂S Production	–	+
Biochemical characters	Urease	–	+
Biochemical characters	Nitrate reductase	–	+
Biochemical characters	β-Galactosidase	+	+
Hydrolysis of	Gelatin	+	+
Hydrolysis of	Aesculin	–	+
Hydrolysis of	Casein	–	+
Hydrolysis of	Tween 40	+	+
Hydrolysis of	Tween 60	+	+
Hydrolysis of	Tween 80	+	+
Acid production from	Glycerol	+	+
Acid production from	Galactose	–	+
Acid production from	D-Glucose	+	+
Acid production from	D-Fructose	+	V
Acid production from	D-Mannose	+	V
Acid production from	Mannitol	+	V
Acid production from	N-Acetylglucosamine	+	+
Acid production from	Amygdalin	+	–
Acid production from	Maltose	+	+
Acid production from	D-Melibiose	–	–
Acid production from	D-Trehalose	+	–
Acid production from	Glycogen	+	+
Acid production from	D-Turanose	+	+

Note: Group-1: Vibrio alginolyticus; Group-2: Vibrio natriegens, Vibrio pelagius, Vibrio azureus; + = Positive; – =Negative; V =Variable

Pathogenic strains

Several species of Vibrio are pathogens. Most disease-causing strains are associated with gastroenteritis, but can also infect open wounds and cause sepsis. They can be carried by numerous marine animals, such as crabs or prawns, and have been known to cause fatal infections in humans after exposure. Risk of clinical disease and death increases with certain factors, such as uncontrolled diabetes, elevated iron levels, and cancer or other immunocompromised states. Pathogenic Vibrio species include V. cholerae, V. parahaemolyticus, and V. vulnificus. ''V. cholerae is generally transmitted by contaminated water. Pathogenic Vibrio species can cause foodborne illness, usually associated with eating undercooked seafood. When ingested Vibrio bacteria can primarily result in watery diarrhea along with other secondary symptoms. The pathogenic features can be linked to quorum sensing, where bacteria are able to express their virulence factor via their signaling molecules. Warmer waters and increased flooding due to climate change promote the growth and spread of Vibrio bacteria.
V. vulnificus outbreaks commonly occur in warm climates and small, generally lethal, outbreaks occur regularly. An outbreak occurred in New Orleans after Hurricane Katrina, and several lethal cases occur most years in Florida. As of 2013 in the United States, Vibrio infections as a whole were up 43% when compared with the rates observed in 2006–2008. V. vulnificus, the most severe strain, has not increased. Foodborne Vibrio infections are most often associated with eating raw shellfish.
V. parahaemolyticus is also associated with the Kanagawa phenomenon, in which strains isolated from human hosts are hemolytic on blood agar plates, while those isolated from nonhuman sources are not hemolytic.
Many Vibrio'' species are also zoonotic. They cause disease in fish and shellfish, and are common causes of mortality among domestic marine life.

Diagnosis

Cholera

A common sign of Vibrio infection is cholera. Cholera primarily presents with rapid water loss by watery diarrhea. Other symptoms include vomiting and muscle cramps. Water loss can lead to dehydration which can be mild to moderate to severe. Moderate to severe dehydration requires immediate treatment. V. cholerae is the most common pathogen that causes cholera. The gold standard for detecting cholera is through cultures of stool samples or rectal swabs. Identification is then done through microscopy or by agglutination of antibodies. Cultures are done in thiosulfate citrate bile-salts sucrose agar. V cholerae will form yellow colonies.

Vibriosis

Vibriosis is a sign of a more severe Vibrio infection. Common causes of vibriosis include consumption of raw or undercooked seafood, primarily oysters, or wound exposure to sea water. The majority of V. parahaemolyticus infections can be self-limiting and symptoms include diarrhea, nausea, headaches, fever and chills. V. vulnificus can lead to a more serious disease, particularly in wound infection which can turn into necrotizing fasciitis. V. parahaemolyticus is the most common pathogen in vibriosis, however V. vulnificus is more common in people who have certain risk factors like older age, liver disease or diabetes mellitus. Like all vibrio diagnosis, vibriosis can also be determined in stool cultures. V. parahaemolyticus and V. vulnificus will form green colonies.

Treatment

Medical care depends on the clinical presentation and the presence of underlying medical conditions.

''Vibrio'' gastroenteritis

Because Vibrio gastroenteritis is self-limited in most patients, no specific medical therapy is required. Patients who cannot tolerate oral fluid replacement may require intravenous fluid therapy.
Although most Vibrio species are sensitive to antibiotics, such as doxycycline or ciprofloxacin, antibiotic therapy does not shorten the course of the illness or the duration of pathogen excretion. However, if the patient is ill and has a high fever or an underlying medical condition, oral antibiotic therapy with doxycycline or ciprofloxacin can be initiated.