Vibrio parahaemolyticus
Vibrio parahaemolyticus,
Vp, is one of many naturally-occurring
Vibrio species that are important in maintaining
the balance of nutrients in the marine environment. They help decompose wastes in the ocean and especially chitin, which comprises the exoskeletin of marine invertebrates such as crabs; chitin is the second most abundant biopolymer on Earth, after cellulose. Unfortunately, some of these marine bacteria, including Vp, are filtered during the feeding process and
high densities of
Vp can occur naturally in oysters. Because
an oyster feeds by filtering seawater, it can accumulate
enough
Vp to cause illness in a vulnerable consumer
who eats uncooked or undercooked oysters. Densities of these naturally
occurring bacteria vary throughout the year in the marine
environment, but they tend to be highest in warmer
months when water temperatures are highest. The
higher the water temperature, the higher the densities of
Vp in the water, and potentially, in oysters.
However, the "old wives tale" that oysters are safe to eat when harvested during months with "r" in their name is not true; in southern states such as the Gulf of Mexico states often maintain infective doses of
Vp throughout the year. Additional information about Vp can be found at the
FDA Food Safety web site.
Predicting Risk
Variations in density drive research efforts to accurately
predict high
Vp densities that could pose health
risks to at-risk individuals who eat raw oysters. The Food
and Drug Administration (FDA) has developed an experimental
prediction model that uses temperature and
salinity to estimate
Vp densities and the associated risk
to consumers.
The University of Southern Mississippi Gulf Coast
Research Laboratory (GCRL) launched a collaboration
in 2003 with federal and state agencies to take the model's
use a step further. GCRL researchers are experimenting
with satellite data on water temperature and other
environmental factors for use in the FDA experimental
prediction model.
Funded by the National Oceanic and Atmospheric
Administration's Oceans and Human Health Initiative,
the breakthrough project initially used sea surface temperature
(SST) data that are already available from satellites. In 2009, salinity data were added to improve the
predictive capability of the maps. More recently, the Naational Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA) have funded this project. The
project now determines how well these remotely sensed data (NASA funding)
match data collected from boats on site in oyster-harvesting
waters (NSF funding).
The ultimate goal of the project is to provide a rigorous real-time
monitoring of
Vp via the maps on this web site.
Remote Sensing
Remote sensing data used in
Vp risk prediction is acquired by the scientists at the Gulf Coast Geospatial Center (GCGC) from NASA's MODerate resolution Imaging Spectroradiometer (
MODIS) satellite sensor onboard the
Aqua satellite. These data go through three steps in order to be used in
Vp risk prediction. First, the amount of the sun's energy (in the form of waves of light) from the waters in the Gulf of Mexico is measured by the MODIS sensor.
Second, four different wavelengths of light measured by MODIS are used in algorithms to estimate sea surface temperature (SST) and salinity. The algorithm for estimating SST uses two measurements of the thermal, or heat energy (in the form of light waves), that radiates from the ocean's surface. The algorithm for estimating salinity uses measurements of two wavelengths of light that are strongly influenced by the amount of suspended (or organic material) and dissolved material (also known as colored dissolved organic material, or CDOM) in the water. Normally, the higher these CDOM measurements are the lower the salinity readings will be, as they are found in higher concentrations near shore where freshwater rivers bring them into the estuaries.
The latest SST, Salinity and Vibrio at Harvest imagery. Click the images for the full resolution geotiff. View the images in GIS Mapserver
In the third step, GCGC scientists apply the algorithm products generated by MODIS data as inputs to algorithms provided by the FDA to estimate densities of
Vp. The density map is created with the following algorithm:
average log(Vp/g) = -2.05 + 0.097*SST + 0.2*SAL - 0.0055*SAL2
The results are illustrated by creating maps that use a color scale from blue (lowest readings) to red (highest readings). These color scales represent the readings of SST, salinity, and estimated
Vp densities that have been generated using MODIS data.
Ground Referencing
Use of remote sensing data must include ground referencing - making certain the algorithm products from the MODIS sensor data significantly match the data someone on a boat at the oyster collection sites can measure with a thermometer or salinometer, and in the laboratory with infected oysters collected at that location. Once scientists find the degree of correlation between the two data collection methods, they can determine the reliability of predictions that are based on remotely sensed data. This process is called "ground truthing".
Steps in Ground Referencing:
Collect oysters, sediment and water samples
GCRL scientists measure water temperature from the
boat with a hand-held thermometer each time they collect,
and they bring oysters, sediment and water samples back to
the lab for analysis of Vp densities.
Prepare samples
The scientists shuck oysters and process oyster meat and
the liquor from the oysters in a blender. They shake water
and sediment samples vigorously and then proceed to process subsamples for Vp.
Incubate samples
Incubating the oyster samples and water samples at on special culture media (see photo)
37oC overnight allows bacteria to reach observable levels on the green culture media (photo)
for analysis the next day.
Identify Vp
A final step in ground referencing is the researchers
use of molecular biology techniques to specifically identify
Vp among the bacterial colonies. They use a filter to pick
up (blot) the bacterial colonies off of the green agar (photo) and then they analyze the bacteria in
the visible colonies with a DNA probe to identify genes that are
specific to Vp, genes such as the thermolabile hemolysin (tlh).
Ground referencing will contribute to fulfilling the project's
objective - development of procedures for generating
accurate and easy-to-use maps that show real-time changes
in predictions of Vp densities. The maps will provide an
important tool for predicting potential health risks to consumers,
and, as a result, will compliment existing fecal indicator tests and help preserve public health.
The public health benefit can also be used as a marketing
tool to educate consumers, maintain consumer confidence
and further enhance the already well-established reputation
of the Mississippi seafood industry.
Further Information
Further information on this project are available in the following documents. Additional scientific information about
Vp can be found in the
"Bad Bugs" manual published by FDA. The
Vp page in the "Bad Bugs Book" is under revision, so please note that the infective dose is not 1,000,000 cells but rather will be changed to a lower number (FDA, personal communication).
Brochure:
Research Article:
Vibrio parahaemolyticus, Vp, is one of many naturally-occurring Vibrio species that are important in maintaining
the balance of nutrients in the marine environment. They help decompose wastes in the ocean and especially chitin, which comprises the exoskeletin of marine invertebrates such as crabs; chitin is the second most abundant biopolymer on Earth, after cellulose. Unfortunately, some of these marine bacteria, including Vp, are filtered during the feeding process and
high densities of Vp can occur naturally in oysters. Because
an oyster feeds by filtering seawater, it can accumulate
enough Vp to cause illness in a vulnerable consumer
who eats uncooked or undercooked oysters. Densities of these naturally
occurring bacteria vary throughout the year in the marine
environment, but they tend to be highest in warmer
months when water temperatures are highest. The
higher the water temperature, the higher the densities of
Vp in the water, and potentially, in oysters.
However, the "old wives tale" that oysters are safe to eat when harvested during months with "r" in their name is not true; in southern states such as the Gulf of Mexico states often maintain infective doses of Vp throughout the year. Additional information about Vp can be found at the
FDA Food Safety web site.