Ecology of Vibrio parahaemolyticus and Vibrio vulnificus in the coastal and estuarine waters of Louisiana, Maryland, Mississippi, and Washington (United States)

Abstract

Vibrio parahaemolyticus and Vibrio vulnificus, which are native to estuaries globally, are agents of seafood-borne or wound infections, both potentially fatal. Like all vibrios autochthonous to coastal regions, their abundance varies with changes in environmental parameters. Sea surface temperature (SST), sea surface height (SSH), and chlorophyll have been shown to be predictors of zooplankton and thus factors linked to vibrio populations. The contribution of salinity, conductivity, turbidity, and dissolved organic carbon to the incidence and distribution of Vibrio spp. has also been reported. Here, a multicoastal, 21-month study was conducted to determine relationships between environmental parameters and V. parahaemolyticus and V. vulnificus populations in water, oysters, and sediment in three coastal areas of the United States. Because ecologically unique sites were included in the study, it was possible to analyze individual parameters over wide ranges. Molecular methods were used to detect genes for thermolabile hemolysin (tlh), thermostable direct hemolysin (tdh), and tdh-related hemolysin (trh) as indicators of V. parahaemolyticus and the hemolysin gene vvhA for V. vulnificus. SST and suspended particulate matter were found to be strong predictors of total and potentially pathogenic V. parahaemolyticus and V. vulnificus. Other predictors included chlorophyll a, salinity, and dissolved organic carbon. For the ecologically unique sites included in the study, SST was confirmed as an effective predictor of annual variation in vibrio abundance, with other parameters explaining a portion of the variation not attributable to SST.

Fig 1

Box plots of sea surface temperature (SST), salinity (Sal), chlorophyll a (Chl-a), dissolved organic carbon (DOC), and SPM (suspended particulate matter) in samples from Washington (WA), Mississippi and Louisiana (Gulf Coast, GC), and Maryland (MD). Box plots summarize distribution by indication of the maximum, 75th percentile, median, 25th percentile, and minimum values. Additional circles indicate outlier values identified by the statistical package R. Points more than 1.5 times the interquartile range above the third quartile or below the first quartile were plotted individually as outliers. Median values are below the graphs.

Fig 2

Model-based estimates of mean and standard deviation (SD) of log abundance by location and gene target. Estimates of mean and SD of log CFU/ml (water) and log CFU/g (oysters and sediment) are based on measurements from DP/CH (all vvhA populations and sediment data), from real-time PCR/MPN (tdh and trh populations in all water and oyster samples, and tlh in WA water and oyster samples), or from both (tlh populations in GC water and oyster samples and in MD water and oyster samples). Values are means with standard deviations of the distributions (not standard errors of the means).

Fig 3

Relative densities of tlh and vvhA populations by habitat and location. The DP/CH-derived tlh population densities were compared to DP/CH-derived vvhA population densities on a sample-to-sample basis for water (A), oysters (B), and sediment (C). Black bars, tlh population densities; gray bars, vvhA population densities; lines with diamonds, sea surface temperature (°C) plotted on the secondary (right) y axis. WA data were excluded from these graphs because of the lack of vvhA organism counts.