In vivo examination of pathogenicity and virulence in environmentally isolated Vibrio vulnificus

Human exposures to the Gram-negative, halophilic environmental pathogen, Vibrio vulnificus, are on the rise, yet pathogenicity and virulence mechanisms remain poorly understood. There are hundreds of cases of Vibrio vulnificus-related infections yearly, and these infections result in hospitalizations 92% of the time, with a mortality rate of 35%. This infection is severe, with patients typically contracting the bacteria via consumption of contaminated food, or through an open wound while swimming in contaminated water, which can result in necrotizing fasciitis and amputation of infected tissue. Several genes have been implicated in contributing to the pathogenicity of this organism (rtxA1, vvpE, vvhA), but no defined mechanism for pathogenicity has been discovered. Here, we focus on environmentally isolated Vibrio vulnificus strains and use a Zebrafish model (Danio rerio) to address the virulence capabilities of these strains. We found that virulence varied greatly between individual strains, and the commonly used marker gene of disease-causing strains of vcgC, did not accurately predict the more virulent strains. To this point, the least virulent strain from the study, V. vulnificus Sept WR1-BW6, which was positive for vcgC, vvhA, and rtxA1, did not produce severe disease in the fish and was the only strain that did not produce a single mortality throughout the study. Our study shows that virulence between different environmental strains varies greatly, and cannot accurately be predicted based on genotype alone.