Gelatin Agar

Principle And Interpretation

Members of the genus Vibrio are facultative anaerobes capable of both respiratory and fermentative metabolism. The natural habitat for Vibrio species is aquatic, in both fresh water and salt water. The growth and biochemical reactivity of most species are enhanced in different test media supplemented with 1-2% sodium chloride. Vibrios are fairly easy to isolate from both clinical and environmental material, though some species may require growth factors and/or vitamins. Media can be made selective for Vibrio's by adding appropriate selective agents (2). High concentrations of NaCl and alkaline pH have also been used to select certain Vibrio species, based on the ability of most Vibrio's to grow at pH values above 8.0 and at 3% or higher concentrations of NaCl. Gelatin Agar is formulated in accordance with APHA (5) for the cultivation and characterization of Vibrio species from foods and faeces. Clinical specimens must be obtained early in the disease as possible because the duration of excretion of the pathogen is short.

Weigh 25 grams of sample such as seafood or vegetables either blended or cut into small pieces and add into 2 flasks. Add 225 ml Alkaline Peptone Water (M618) to one flask and 225 ml of Glucose Phosphate Broth (M070) in another flask. Mix well. Incubate at 35° ± 2°C for 6 to 8 hours. Inoculate one loopful from each flask on the non-selective Gelatin Agar.

V.cholerae appear transparent and usually have a characteristic cloudy zone around colony, which becomes more definite after few minutes of refrigeration. When these colonies are viewed in oblique light they appear iridescent green to bronze coloured and finely granular.