Description
Vibrio’s are fairly easy to isolate from both clinical and environmental materials, though some species may require growth factors and /or vitamins. Vibrio parahaemolyticus is the leading cause of bacterial diarrhoea associated with the consumption of contaminated food products. Media can be made selective for Vibrios by adding appropriate selective agents. High concentrations of sodium chloride have been used to select certain Vibrio species, based on the ability of most Vibrio’s to grow at 3% or higher concentrations of NaCl. Tryptone Soya Salt Agar with Magnesium Sulphate (TSAMS) is recommended by APHA for enumerating V.parahaemolyticus from seafood by membrane filter technique. The medium is used after the seafood sample is diluted (1:10) with sterile Peptone Tween Salt Diluent (PTS), blended for 60 secs at high speed and filtered through Hydrophobic Grid Membrane Filter (HGMF). With forceps, aseptically transfer the HGMF from the filtration apparatus to the surface of a dry Tryptone Soya Salt Agar with Magnesium Sulphate and incubate. Following incubation for 4 hours at 35?C, HGMF is aseptically transferred from TSAMS to the surface of dry Vibrio Parahaemolyticus Sucrose Agar. Following incubation, V.parahaemolyticus colonies on VPSA will be blue- green coloured since they are sucrose non-fermenters, and other growth will be yellow. Count green-blue colonies and calculate the MPN per gram of seafood.
