Environmental factors and reservoir shifts contribute to the seasonality of pathogenic Vibrio species
Turner, Jeffrey Wayne
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Members of the Vibrio genus are autochthonous inhabitants of marine coastal and estuarine ecosystems worldwide. Although Vibrio exist in the marine environment as common heterotrophic bacteria, a small percentage of environmental strains carry the genetic determinants for human pathogenesis. In particular, V. cholerae, V. parahaemolyticus and V. vulnificus are significant pathogens of humans worldwide. In a series of studies, we investigated the potential drivers of Vibrio prevalence along the coastal reaches of Georgia, USA. Surface water temperature, salinity and dissolved oxygen (DO) were strongly associated with the prevalence of total Vibrio (cultured on thiosulfate citrate bile sucrose agar, TCBS) and the prevalence of virulent and avirulent V. cholerae and V. vulnificus (PCR detection of species-specific and virulence-associated gene targets) (P < 0.05 for each). However, each species responded differently to seasonal changes in environmental parameters. For example, V. parahaemolyticus (species-specific gene target) was detected year round even when water temperatures fell below 10oC. Interestingly, the prevalence of genes associated with virulent strains of V. parahaemolyticus was strongly associated with temperature (P < 0.05). Regardless, relationships with environmental parameters alone were unable to capture the complexity of Vibrio seasonality in this study. The prevalence of V. cholerae, V. parahaemolyticus and V. vulnificus was shown to be associated with the abundance of specific plankton taxa (copepods, diatoms and decapods, respectively) (P < 0.05 for each). Additionally, peaks in the prevalence of V. cholerae were associated with peaks in the abundance of detrital particulate organic matter (POM), which coincided with the periodicity of phytoplankton blooms in this region. These findings led to the application of a GFP-tagged V. cholerae strain to investigate and document associations between V. cholerae and the copepod (an important environmental host). Overall, these investigations confirm temperature and salinity as Vibrio drivers. Furthermore, these investigations support the hypothesis that shifts in the abundance of specific plankton taxa and detrital POM are associated with the seasonal distribution of pathogenic Vibrio species.