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

Examine the plates after 24 h. Measure the zone of inhibition and record. See thezone interpretative chart given by the supplier of antibiotic discs and record as sensitive orresistant.ESTIMATION OF TOTAL VIABLE BACTERIAL COlJNT IN WATEII SAMPLEEstimation of total v!able count (TVC) is used to determine the density of livingbacteria in a sample. A simple serial dilution of the water sample followed by spread plate orpour plate method is employed to achieve this objective. The sample is diluted scrially insterile normal saline solution. 'She serial dilution helps to reduce the nu~nbcr of bacteria in themcdiun~ to ~nanageable limit as the plates showing 30-300 colonies are considercd countableWhen a diluted sample is plated, the number of colonies produccd can be used to calculatethe original cell density in the sample using the formula as follows:Bacterial count (TVC) = No. ofcolr~nics observed XImI of sample plated Dilution factorSince it is virtually irnpossiblc to know ifthe colon~es produccd on plates or~ginated with asinglc cell or a cluster of cells the tcrm Colony forming unit (cfi~)/ml is used instead ofExampleSay the number of colonies counted on the plate = 55Volume of diluted sample plated = 0.1 mlDilution factor in the tube from which the sample was taken for plating - 10'I-lence total no. of bacteria in the sample = 55 x 1 = 550 x 105 --0.1