Question You receive a sample of egg that it is believed to

Question: You receive a sample of egg that it is believed to contain approximately 10^8 cfu g^-1 of Salmonella. Design dilution series spread plate and MPN assays to more precisely quantify the number of Salmonella in the sample.

Solution

Stock concentration is, 10^8 cfu g^-1

Step 1: Tube 1 (10^8 cfu/g), take 0.1 g and transfer into a tube 2, make up the volume upto1 ml with the diluent ---------> Gives 10-1 diluted solution (10 fold diluted). The solution concentration is, 10^7 cells/ml

Step 2: Take 0.1 ml and transfer into a tube 3, make up the volume upto10 ml with the diluent ---------> Gives 10-2 diluted solution (100 fold diluted) of tube 2. The solution concentration is, 10^5 cells/ml

Step 3: Take 0.1 ml from tube 3 and transfer into a tube 4, make up the volume upto10 ml with the diluent ---------> Gives 10-2 diluted solution (100 fold diluted) of tube 3. The solution concentration is, 10^3 cells/ml.

Step 4: : Take 0.1 ml from tube 4 and transfer into a tube 5, make up the volume upto10 ml with the diluent ---------> Gives 10-2 diluted solution (100 fold diluted) of tube 4. The solution concentration is, 10 cells/ml.