HiCrome™ Vibrio HiVeg™ Agar

Principle And Interpretation

Vibrio' s have played a significant role in human history. Outbreaks of cholera, caused by Vibrio cholerae, can be traced back in time to early recorded descriptions of enteric infections. The Vibrio's have also received the attention of marine microbiologists who observed that the readily cultured bacterial population in near-shore waters and those associated with fish and shell fish were predominantly Vibrio species (1). Vibrio species are mainly responsible for causing cholera and food poisoning in humans. Vibrio cholerae causes cholerae due to the intake of contaminated food such as raw oysters. Vibrio parahaemolyticus is a major cause of food borne infections, causing food poisoning (2). Since Vibrio species naturally occur in sea water, worth special mention is their need for sodium chloride, although some species can grow with minimum sodium chloride concentration (1). The widely used media for Vibrio isolation are TCBS Agar and Alkaline Peptone Water (3). However accompanying sucrose-fermenting bacteria pose a problem in the identification of Vibrio species on TCBS Agar. On HiCrome® Vibrio Agar, the colour development by Vibrio species in not affected by the presence of colonies of other bacteria. This is because, the amount of colour developed depends on the reaction of the bacterial beta-galactosidase with the substrate contained in the media (4). HiCrome® Vibrio HiVeg® Agar is same as HiCrome® Vibrio Agar except that the animal based peptones are completely replaced with vegetable peptones to avoid the BSE/TSE risks associated with animal peptones.

HiVegⓇ peptone provides carbonaceous, nitrogenous and essential nutrients to the organisms. High concentration of sodium chloride in addition to maintaining the osmotic equilibrium also has an inhibitory action on the accompanying microflora. Sodium thiosulphate, sodium citrate and Synthetic detergent no. IV are used in the formulation because they can inhibit the growth of gram positive and some gram negative bacteria, but not members of Enterobacteriaceae. The proprietary chromogenic mixture incorporated in the medium helps in the chromogenic differentiation of Vibrio cholerae and Vibrio parahaemolyticus. The high (alkaline) pH of the medium helps in selective isolation of Vibrio species.