Biochemical and Virulence Characterization of Vibrio vulnificus Isolates From Clinical and Environmental Sources

Abstract

Vibrio vulnificus is a deadly human pathogen for which infections occur via seafood consumption (foodborne) or direct contact with wounds. Virulence is not fully characterized for this organism; however, there is evidence of biochemical and genotypic correlations with virulence potential. In this study, biochemical profiles and virulence genotype, based on 16S rRNA gene (rrn) and virulence correlated gene (vcg) types, were determined for 30 clinical and 39 oyster isolates. Oyster isolates were more biochemically diverse than the clinical isolates, with four of the 20 tests producing variable (defined as 20–80% of isolates) results. Whereas, for clinical isolates only mannitol fermentation, which has previously been associated with virulence potential, varied among the isolates. Nearly half (43%) of clinical isolates were the more virulent genotype (rrnB/vcgC); this trend was consistent when only looking at clinical isolates from blood. The majority (64%) of oyster isolates were the less virulent genotype (rrnA or AB/vcgE). These data were used to select a sub-set of 27 isolates for virulence testing with a subcutaneously inoculated, iron-dextran treated mouse model. Based on the mouse model data, 11 isolates were non-lethal, whereas 16 isolates were lethal, indicating a potential for human infection. Within the non-lethal group there were eight oyster and three clinical isolates. Six of the non-lethal isolates were the less virulent genotype (rrnA/vcgE or rrnAB/vcgE) and two were rrnB/vcgC with the remaining two of mixed genotype (rrnAB/vcgC and rrnB/vcgE). Of the lethal isolates, five were oysters and 11 were clinical. Eight of the lethal isolates were the less virulent genotype and seven the more virulent genotype, with the remaining isolate a mixed genotype (rrnA/vcgC). A discordance between virulence genotype and individual mouse virulence parameters (liver infection, skin infection, skin lesion score, and body temperature) was observed; the variable most strongly associated with mouse virulence parameters was season (warm or cold conditions at time of strain isolation), with more virulent strains isolated from cold conditions. These results indicate that biochemical profiles and genotype are not significantly associated with virulence potential, as determined by a mouse model. However, a relationship with virulence potential and seasonality was observed.

Variable Freshwater Influences on the Abundance of Vibrio vulnificus in a Tropical Urban Estuary

“…The importance of distinguishing the C-type when assessing exposure risks in recreational waters is not clear. Both genotypes cause infections in humans and either type can be lethal in mouse models ( 46 ). Comparison of the 16 lethal strains in that study indicates, however, that the average percent mortality was significantly lower for E-type than for C-type ( n = 8 for each type; t test, P = 0.0028).…”

Purpura fulminans due to Vibrio vulnificus severe infection

“…This bacillus is the deadliest foodborne pathogen with a fatality rate greater than 30 %, however, severity of this condition will depend too on host’s comorbidities [7] .…”

“…Two main routes of entry into the bloodstream have been identified in the development of this infection; ingestion of contaminated raw seafood, mainly oysters, and direct bacterial inoculation of skin wounds by direct contact between open wounds and contaminated seawater, or by skin trauma when fishing, handling, or preparation of seafoods [4] , [5] , [7] .…”

“…Biotype 1 strains are responsible of most infections in humans, while biotype 2 strains (non-pathogenic for humans) are responsible for infections in marine eels. The strains of biotype 3, which cause fewer skin infections in humans, have been limited to people who handle fish [6] , [7] .…”

Genetic Divergence of Vibrio vulnificus Clinical Isolates with Mild to Severe Outcomes

“…A mouse model study of environmental and clinical strains found that isolates with the vcgC allele were more common in clinical strains and were more likely to cause severe infection and death, but isolates with the vcgE allele also were capable of causing lethal infections ( 14 ). Another mouse study utilized strains both from clinical and environmental sources and found no difference in virulence between vcgC and vcgE strains, although isolates obtained from colder temperature seasons were more virulent ( 15 ). Thus, despite many attempts to categorize V. vulnificus , the predictive value of genetic analysis, biochemical assays, and phylogeny to predict pathogenic potential remains unclear.…”