Vibrio vulnificusis a Gram-negative,facultative anaerobic, curved rod-shaped, motile, Gammaproteobacteria of theVibriogenus in the Vibrionaceae family.It is one human pathogenic species of theVibriogenus together withVibrio choleraeandVibrio parahaemolyticus.
- V. vulnificuswas first described as a separate bacterial species in late 1976 when it was initially namedBeneckea vulnificaand later it was named asVibrio vulnificusin 1979. It is mainly found in warm seawater and estuarine environments. It is frequently reported to cause gastroenteritis, septicemia, and wound infections.
- Biotyping has dividedV. vulnificusinto three biotypes; biotype 1 is associated with human infections, biotype 2 is associated with human and fish (eel) infections, and biotype 3 is associated with wound infections in fish handlers.
Vibrio vulnificusClassification
| Domain | Bacteria |
| Phylum | Pseudomonadota |
| Class | Gammaproteobacteria |
| Order | Vibrionales |
| Family | Vibrionaceae |
| Genus | Vibrio |
| Species | V. vulnificus |
Habitat ofVibrio vulnificus
- V. vulnificusis a marine bacterial species. It is normally found in coastal areas, estuaries, brackish water, deltas, and other places with warm saline water globally. It is also reported from deeper ocean surfaces as well.
- Primarily,V. vulnificus与海洋动物喜欢oy吗sters (primarily), shellfish, crabs, and even higher fishes. Through such kinds of seafood, they come into contact with humans and cause disease.
Morphology ofVibrio vulnificus
- V. vulnificusshows pleomorphism. They are commonly found in two morphologically distinct forms; circular during the dormantviable non-culturable (VBNC) state androd-shaped (curved)during the active state.
- In the VBNC state, they appear as small cocci measuring 0.3 μm in diameter. This stage is found in low-nutrition and low-temperature (5°C or below) environments.
- In a normal active state, they appear as curved bacilli measuring 3 μm long and 0.7 μm wide.
Cultural Characteristics ofVibrio vulnificus
- For the culture ofVibrio spp.,the sample must be first enriched in an enrichment broth like Alkaline Peptone Water, and then it can be cultured in different mediums for selective isolation and identification.
- Diverse types of culture mediums can be used for the isolation ofV. vulnificus, the most commonly used ones include TCBS (thiosulfate citrate bile salt sucrose) agar medium, CHROMagar Vibrio medium, Blood agar medium, and Tryptic Soy medium.
- Selective mediums are also available like mCPC (modified cellobiose polymixin B colistin) medium, andVibrio vulnificusmedium (VVM). This medium contains antibiotics like Polymixin B and colistin, alkaline pH, and moderate salt concentration which suppresses the growth of other organisms.
- InTCBS medium,V. vulnificusproduces small, circular, green colonies.
- InBlood agarmedium,V. vulnificusproduces small (about 3 mm), smooth, creamy, or greyish-white colored, non-hemolytic or α- hemolytic colonies.
Biochemical Characteristics ofVibrio vulnificus
General Biochemical Tests
| General Biochemical Characteristics | Vibrio vulnificus |
| Capsule | Variable |
| Catalase | Positive (+) |
| Citrate | Negative (-) for clinical isolatesVariable for environmental isolates |
| Flagella | Positive (+) |
| Gas | Negative (-) |
| Gram Staining | Gram Negative Bacilli |
| H2S (Hydrogen Sulfide) | Negative (-) |
| Indole | Positive (+) for clinical isolatesVariable for environmental isolates |
| Motility | Motile |
| Methyl Red (MR) | Positive (+) |
| Nitrate Reduction | Positive (+) |
| Oxidase | Positive (+) |
| ONPG Test | Positive (+) (Except biotype 3 members) |
| OF (Oxidative Fermentation) | Facultative anaerobe |
| Growth on 1% to 6% NaCl | Positive (+) |
| TSI Test | A/A, no gas, no H2S |
| Urease | Negative (-) |
| Voges-Proskauer (VP) | Negative (-) |
Carbohydrate Fermentation Tests
| Carbohydrate Fermentation Tests | Vibrio vulnificus |
| L-Arabinose | Negative (-) |
| Amygdalin | Positive (+) |
| D-Adonitol | Negative (-) |
| Cellobiose | Positive (+) (Except biotype 3 members) |
| Dulcitol | Negative (-) |
| D-Galactose | Positive (+) |
| Glucose | Positive (+) |
| Inositol | Negative (-) |
| Glycerol | Negative (-) |
| Lactose | Positive (+) (Except biotype 3 members) |
| Melibiose | Negative (-) |
| Maltose | Positive (+) |
| Mannitol | Variable |
| D – Mannose | Positive (+) |
| Rhamnose | Negative (-) |
| Raffinose | Negative (-) |
| 山梨糖醇 | Variable |
| Sucrose | Negative (-) |
| Trehalose | Positive (+) |
| Xylose | Negative (-) |
Enzymatic Hydrolysis Tests
| Enzymatic Hydrolysis Tests | Vibrio vulnificus |
| Arginine Dehydrolase | Negative (-) |
| DNase | Positive (+) |
| Esculin Hydrolysis | Variable |
| Gelatinase | Positive (+) |
| Lysine Decarboxylase | Positive (+) |
| β-Galactosidase | Positive (+) |
| Ornithine Decarboxylase | Positive (+) in clinical samplesVariable in environment isolates |
| Tryptophan Deaminase | Negative (-) |
Vibrio vulnificusAssociated Diseases and Outbreaks
- Vibrio vulnificusis a deadly pathogenicVibrio人类物种,导致疾病和一些3月ine life. In human,V. vulnificusare primarily associated with wound infections, gastroenteritis, and septicemia. It is the leading cause of death and disease associated with seafood in the USA and coastal areas and is accountable for about 90% of deaths caused byVibriospecies in those areas.
- The mortality rate inV. vulnificusinfection is very high – 25% in wound infection, about 50% in septicemia, and around 33% in gastroenteritis – even with treatment. This higher mortality is mainly due to endotoxin shock and vulnerabilities in patients with liver disease, immunocompromised state, diabetes, HIV, etc.
- V. vulnificusdisease outbreaks are frequently reported in the USA, usually in the summer months. The countries with the most documented cases ofV. vulnificusare the United States, South Korea, Taiwan, Japan, and Mexico. Coastal areas in the Southeastern United States like Florida, Texas, Alabama, Louisiana, Mississippi, and other nearby areas have higher incidences ofV. vulnificusinfections. The Gulf of Mexico is another hot zone for outbreaks ofV. vulnificus-associated infections. Coastal areas of Asia, the Middle East, and warm areas in Europe are also endemic zones.
Virulence Factors ofVibrio vulnificus
A variety of virulence factors have been identified inV. vulnificuswhich contributes to disease pathogenesis. Some of the important virulence factors are listed below.
- Polysaccharide Capsule:This helps the pathogens to escape the phagocytic effect of human immune cells.
- Endotoxin:The lipopolysaccharide of this bacterium is not potent enough to activate the immune system to produce cytotoxic TNF and cytokines; however, LPS induces inflammatory responses in wound infections. The capsular proteins are capable of triggering an immune response causing shock in the patient.
- Exotoxin:Extracellular cytolysin/hemolysin, MARTX toxin, and metalloproteases are toxic compounds secreted by this bacterium which results in host cell/tissue destruction and helps in their dissemination.
- Iron Acquisition from Transferrin:V. vulnificuscan capture iron bound to transferrin and use it in their metabolism.
Laboratory Diagnosis/Identification ofVibrio vulnificus
V. vulnificusand its infections are confirmed using several techniques including culture and biochemical identification, serological analysis, and molecular analysis.
1. Microscopy and Biochemical Characterization
Clinical specimens like blood, wound swabs, stool, and tissue biopsy are cultured on a suitable medium (commonly TCBS) and the developed colonies are studied macroscopically and microscopically and characterized biochemically.
2. Immunological Detection
ELISA and agglutination tests are used to detectV. vulnificusantigens in samples and antibodies againstV. vulnificusantigens in the patient’s serum.
3. Molecular Methods
Polymerase chain reaction (PCR) is the most rapid and accurate method to detect and confirm the presence ofV. vulnificusin any specimen. Colony hybridization tests and DNA probe assays are also available for their rapid identification.
References
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- Amalina, N.Z., Santha, S., Zulperi, D. et al. Prevalence, antimicrobial susceptibility and plasmid profiling of Vibrio spp. isolated from cultured groupers in Peninsular Malaysia. BMC Microbiol 19, 251 (2019). https://doi.org/10.1186/s12866-019-1624-2
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