A Rapid and Simple PCR Analysis Indicates There Are Two Subgroups of Vibrio vulnificus Which Correlate with Clinical or Environmental Isolation

Abstract

Vibrio vulnificus is an estuarine bacterium which is the causative agent of both food-borne disease and wound infection. Although V. vulnificus is commonly found in molluscan shellfish at high numbers, the incidence of disease is relatively low, leading to the hypothesis that not all strains of V. vulnificus are equally virulent. Unfortunately, there is currently no easy test to identify virulent strains of this species. We have previously identified a 200 bp randomly amplified polymorphic DNA (RAPD) PCR amplicon associated with clinical isolates. DNA sequence data from this locus in six clinical and four environmental isolates showed that the strains could be divided into two groups, which we termed C-type (correlates with clinical origin) and E-type (correlates with environmental origin). We designed PCR primers that could distinguish between the two groups, and typed 55 randomly selected strains. We found that 90% of the C-type strains were clinical isolates, while 93% of environmental isolates were classified as E-type. The region directly downstream of this locus contained a heptanucleotide sequence repeated various times depending on the strain. Using a PCR-based assay to detect the repeat number present in a given strain, we found a statistically significant correlation with the C/E type classification and the number of repeats. The data reported here are consistent with the existence of two genotypes of V. vulnificus, with the C-type being a strong indicator of potential virulence.