Environmental Determinants of Vibrio parahaemolyticus in the Chesapeake Bay

Abstract

<i>Vibrio parahaemolyticus</i> naturally occurs in brackish and marine waters and is one of the leading causes of seafood-borne illness. Previous work studying the ecology of <i>V. parahaemolyticus</i> has often been limited in geographic extent and lacked a full range of environmental measures. This study used a unique large data set of surface water samples in the Chesapeake Bay (<i>n</i> = 1,385) collected from 148 monitoring stations from 2007 to 2010. Water was analyzed for more than 20 environmental parameters, with additional meteorological and surrounding land use data. The <i>V. parahaemolyticus</i>-specific genetic markers thermolabile hemolysin (<i>tlh</i>), thermostable direct hemolysin (<i>tdh</i>), and <i>tdh</i>-related hemolysin (<i>trh</i>) were assayed using quantitative PCR (qPCR), and interval-censored regression models with nonlinear effects were estimated to account for limits of detection and quantitation. <i>tlh</i> was detected in 19.6% of water samples; <i>tdh</i> or <i>trh</i> markers were not detected. The results confirmed previously reported positive associations for <i>V. parahaemolyticus</i> abundance with temperature and turbidity and negative associations with high salinity (>10 to 23‰). Furthermore, the salinity relationship was determined to be a function of both low temperature and turbidity, with an increase of either nullifying the high salinity effect. Associations with dissolved oxygen and phosphate also appeared stronger when samples were taken near human developments. A renewed focus on the <i>V. parahaemolyticus</i> ecological paradigm is warranted to protect public health.<b>IMPORTANCE</b> <i>Vibrio parahaemolyticus</i> is one of the leading causes of seafood-borne illness in the United States and across the globe. Exposure is often through consuming raw or undercooked shellfish. Given the natural presence of the bacterium in the marine environment, an improved understanding of its environmental determinants is necessary for future preventative measures. This analysis of environmental <i>Vibrio parahaemolyticus</i> is one of only a few that utilize a large data set measured over a wide geographic and temporal range. The analysis also includes a large number of environmental parameters for <i>Vibrio</i> modeling, many of which have previously only been tested sporadically, and some of which have not been considered before. The results of the analysis revealed previously unknown relationships between salinity, turbidity, and temperature that provide significant insight into the abundance and persistence of <i>V. parahaemolyticus</i> bacterium in the environment. This information will be essential for developing environmental forecast models for the bacterium.