Vibrio vulnificus dynamics in a south Texas bay

Vibrio vulnificus is a human pathogen commonly found in coastal and estuarine waters in temperate and subtropical regions across the world. The ecology of V. vulnificus has been studied in these regions primarily using cultured-based methods for enumeration of V. vulnificus from the environment. Optimal temperature and salinity ranges have been established, but relationships with other environmental parameters have not been studied as extensively. The primary objective of this study was to better understand the ecology of V. vulnificus and how environmental parameters found in south Texas bays and estuaries regulate its distribution. A recently developed molecular biological technique for the direct enumeration of V. vulnificus from estuarine water column samples was used to test three hypotheses:

1. V. vulnificus makes up a greater percentage of the total bacterial population in the water column under low oxygen conditions; 2) Powderhorn Lake serves as a pointsource for V. vulnificus in Matagorda Bay; 3) Higher V. vulnificus concentrations are found in the water column when oyster reefs are present. These hypotheses were formed to improve predictive models, identify potential hot-spots for V. vulnificus in the water column, and to better inform stakeholders as to when and where risk of infection might be greatest. Dissolved oxygen was rarely low enough in the environment to stress aerobic bacteria in the water column, so the first hypothesis could not be appropriately tested. Neither higher concentrations nor detection frequencies of V. vulnificus were found in Powderhorn Lake compared to the rest of the bay, so Powderhorn Lake was not identified as a point-source for V. vulnificus. Higher concentrations and detection frequencies of V. vulnificus were not found at sites with oyster beds, so oyster beds cannot be used as indicators of higher concentrations of V. vulnificus in the water column. Interestingly, patchiness of V. vulnificus was observed temporally and spatially throughout the sampling region of Matagorda Bay, on a scale that has not been frequently examined. Variation occurred between samples in close proximity to one another, as well as between sampling dates. This distribution exhibited a small scale patchiness not frequently reported in past studies.