Genotype Is Correlated with but Does Not Predict Virulence of Vibrio vulnificus Biotype 1 in Subcutaneously Inoculated, Iron Dextran-Treated Mice

Abstract

Vibrio vulnificus is the leading cause of reported deaths from infections related to consumption of seafood in the United States. Affected predisposed individuals frequently die rapidly from sepsis. Otherwise healthy people can experience severe wound infection, which can lead to sepsis and death. A question is why, with so many people consuming contaminated raw oysters, the incidence of severe V. vulnificus disease is low. Molecular typing systems have shown associations of V. vulnificus genotypes and the environmental or clinical source of the strains, suggesting that different genotypes possess different virulence potentials. We examined 69 V. vulnificus biotype 1 strains that were genotyped by several methods and evaluated them for virulence in a subcutaneously inoculated iron dextran-treated mouse model. By examining the relationships between skin infection, systemic liver infection, and presumptive death (a decrease in body temperature), we determined that liver infection is predicated on severe skin infection and that death requires significant liver infection. Although most strains caused severe skin infection, not every strain caused systemic infection and death. Strains with polymorphisms at multiple loci (rrn, vcg, housekeeping genes, and repetitive DNA) designated profile 2 were more likely to cause lethal systemic infection with more severe indicators of virulence than were profile 1 strains with different polymorphisms at these loci. However, some profile 1 strains were lethal and some profile 2 strains did not cause systemic infection. Therefore, current genotyping schemes cannot strictly predict the virulence of V. vulnificus strains and further investigation is needed to identify virulence genes as markers of virulence.Vibrio vulnificus is a halophilic bacterium that is naturally present in estuarine waters and contaminates oysters and other shellfish. It is an opportunistic pathogen of humans that causes primary septicemia and wound infection in susceptible hosts and is the leading cause of reported seafood-related deaths due to infection in the United States (for a review, see reference 17). V. vulnificus strains are divided into three biotypes, with human disease caused predominantly by biotype 1 and disease of eels caused predominantly by biotype 2. Biotype 3 was recently isolated from wound infections in Israel and represents an emerging form of this species (3). Several factors have been definitively shown to contribute to virulence of V. vulnificus, including capsular polysaccharide (60), the ability to acquire iron (38, 45, 61), type IV pili (46), flagella (37, 47), RTX toxin (30, 35, 39), and others (17, 27). To date, no single factor has been identified that can distinguish between naturally occurring virulent and less virulent isolates of V. vulnificus.In susceptible humans, V. vulnificus causes a rapid, fulminating disease process resulting in extensive tissue damage (reviewed in reference 17). Primary septicemia is characterized by high fever, chills, hypotension, and septic shock. ...

Genotypic Diversity and Virulence Characteristics of Clinical and Environmental Vibrio vulnificus Isolates from the Baltic Sea Region

“…All cluster II strains possessed pilF type C, which has previously been correlated with pathogenicity (1,28) and was only rarely found in cluster I BT1 strains. In contrast to the study of Roig et al (28), in which nearly all clinical isolates possessed the pilF type C allele, more than half of the clinical strains in our strain collection possessed pilF type E. Altogether, our data on the distribution of type C and E alleles of the pilF, 16S rRNA, and vcg genes among environmental and clinical isolates from the Baltic Sea region support the opinion of Thiaville et al that E-type strains can be pathogenic and should not be classified as avirulent per se (31).…”

“…Other key genes that may differentiate between the genomes of clinical and environmental genotypes were recently identified using a comparative genome analysis approach (29), and Kim et al identified further potential virulence factors by comparative transcriptomic analyses between clinical and environmental isolates using a cDNA microarray (30). Thiaville et al analyzed the virulence properties of 33 clinical and 36 environmental isolates of V. vulnificus biotype 1 from the United States in a mouse model and found that higher virulence was correlated with, but not exclusive to, the clinical genotype (31). While several studies examined the distribution and characteristics of this species from tropical regions and the United States, studies on pathogenic and nonpathogenic V. vulnificus strains from northern temperate waters are scarce.…”

Role of Anaerobiosis in Capsule Production and Biofilm Formation in Vibrio vulnificus

“…Of V. vulnificus strains isolated from clinical cases, 90% have the vcgC allele (C-genotype), while 87% of environmental isolates have the vcgE (E-genotype) allele (4,7). Although genotype correlates with virulence, it is not necessarily predictive, as shown by Thiaville et al They found that 3 of the 9 most virulent strains, when inoculated subcutaneously in iron dextran-treated mice, possessed the vcgE allele, which confirms that not only those strains with the vcgC allele are capable of causing disease (8).…”

Molecular and Physical Factors That Influence Attachment of Vibrio vulnificus to Chitin

“…Despite these studies, no single, causal virulence factor has been found to be exclusively associated with clinical genotype strains (17). While the C/E genotyping scheme strongly correlates with virulence potential, this method does not strictly predict virulence (17).…”

“…While the C/E genotyping scheme strongly correlates with virulence potential, this method does not strictly predict virulence (17). For example, some strains with the vcgE allele have been isolated from clinical cases, often from wound infections.…”