Genetic distinctions among clinical and environmental strains of Vibrio vulnificus

Abstract

Vibrio vulnificus causes rare but frequently fatal septicemia associated with raw oyster consumption by persons with underlying hepatic or immune system dysfunction. The virulence potential of environmental reservoirs appears widely distributed, because most strains are virulent in animal models; however, several investigations recently demonstrated genetic divergence among strains from clinical versus environmental origin at independent genetic loci. The present study used PCR to screen DNA polymorphisms in strains from environmental (n = 35) or clinical (n = 33) sources, and genomic relationships were determined by repetitive extragenic palindromic DNA PCR (rep-PCR) typing. Significant (P < 0.01) association was observed for typical "clinical" or "environmental" polymorphism profiles based on strain origin. Most oyster isolates (88%), including all of those with the "environmental" profile, also formed a single rep-PCR genogroup. Clinical isolates within this group did not have the typical "clinical" profile. On the other hand, clinical isolates with the typical polymorphism profile were distributed among multiple rep-PCR genogroups, demonstrating greater genetic diversity than was evident by profiling genetic polymorphisms. Wound isolates were genetically distinct from typical blood isolates by all assays. Strains from an outbreak of wound infections in Israel (biotype 3) were closely related to several U.S. strains by rep-PCR, indicating potential reservoirs of emerging disease. Strains genetically related to blood isolates appeared to be relatively rare in oysters, as only one had the "clinical" polymorphism profile or clustered by rep-PCR. However, this study was not an extensive survey, and more sampling using rep-PCR for sensitive genetic discrimination is needed to determine the virulence potential of environmental reservoirs.

FIG. 1.

Comparison of rep-PCR analysis and genotype profiles for clinical and environmental strains of V. vulnificus. A scale for rep-PCR similarity is shown at the bottom of the figure. Strain sources are described in detail in the text, and a description of strains in the table includes the following: S, septicemia from oyster consumption; W, wound infection; O, oyster; E, environmental, not oyster; F, fatal outcome of infection; R, recovered from infection. Strains from septicemia origins are shaded in black, wound infection isolates are shaded in gray, and environmental isolates are not shaded. Where available, information on the site and date of isolation of strains is provided; alternatively, the date that the strains first appeared in publication is shown (asterisk). Specific genotype profiles were determined by PCR as described in the text and included the following: 16S rRNA gene (type A, B, or A+B), group 1 CPS genes (alleles 1 and 2; a dash is used to indicate where CPS primers did not amplify), and RAPD-associated locus (C type and E type). Typical “clinical” profiles (16S B, CPS allele 1, and RAPD C type) are shaded in black, “environmental” profiles (16S A or A+B, CPS allele 2 or CPS negative, and RAPD E type) are not shaded, and atypical combinations are shaded in gray.