, Diagnosis an-&& of Shrimp Diseases - Central Institute of ...

Incubate at 37°C for 1-2 h.Examine the colour change of the broth from colourless to yellow.Inferprelation: Development of yellow colour indicates positive activity for P-galactosidaseactivity, (fermentation of lactose).Nitrate reductionPrinciple: Bacteria can assimilate inorganic nitrate into their proteins by virtue of one of theenzymes in a complex process called nitrate reductase, which converts nitrate to nitrite(N03+N02). NO2 is detected by an inorganic assay using a-naphthylamine and sulfanilicacid.Procedure:i. Inoculate test culti~re of bacteria to tubes containing about 2 ml of nutrient brothsupplemented with 0.1% KN03 and 0.2% agar.ii. Incubate at 37°C for 24 11.iii.Add 1 ml each of a-napathylami~ie solution and Sulfanilic acid solution.Inierpretrrtion: Positive reaction (conversion of NO3-+NOz) is indicated by development ofpink colour.Note: When there is no development of pink colouration, add a pinch of 7inc dust. Absenccof colouration indicates positive result for the reaction N03-+N02.Indole testPrinciple: Indole is produced upon degradation of tryptophan by some bacteria. Production ofindole is detected by formation of pink coloured compound when it reacts with an aldehydesucl~ as p-dimethyl amino benzaldehyde.Procedure:i. Grow bacteria in 1% peptone water broth for 24 h at 37°C.ii. Observe for turbidity indicative of growth.iii.Add 0.5 ml of Kovac's reagent to the broth culture of bacteria and shake gently.iv. Observe for development of pink colour.