INDOLE NITRATE MEDIUM (TRYPTONE NITRATE MEDIUM) (VEG.)

Description

This medium is prepared by replacing Casein enzymic hydrolysate with Veg hydrolysate which is free of BSE/ TSE risks. This medium can be used against animal based Indole Nitrate medium for identification of microorganisms based on nitrate reduction and indole tests. Indole production can be detected by the addition of Kovac?s Indole reagent or Ehrlich?s aldehyde reagent. The formation of a pinkish red colour within 10 seconds in the reagent layer after gentle agitation indicates positive indole test. Potassium nitrate in the medium acts as the substrate for nitrate reduction by microorganisms. Certain bacteria convert nitrate to nitrite, ammonia or nitrogen gas. The presence of nitrite is determined by addition of 0.5 ml of each of Sulphanilic Acid and alpha – Naphthylamine solution. The development of red violet colour indicates nitrate reduction to nitrite. If no colour develops, it means that either nitrate is not reduced or further reduction to ammonia or nitrogen gas has taken place. This can be verified by adding a pinch of zinc dust to the tube. Zinc reduces nitrate to nitrite resulting in a red colour. The red colour indicates that nitrate is still present and was not reduced previously. An absence of red colour after the addition of zinc dust indicates that no nitrate is present, and thus the nitrate was reduced further than nitrite. Therefore, the nitrate reduction test is evidenced by either the presence of a catabolic end product or the absence of nitrate in the medium.