g) Voges-proskauer (VP) medium
Procedure Preparation of food homogenate
Wigh 25 gm of the mixed sample aseptically into a sterile blender jar or into astomacher bag and add 225ml of buffered peptone water(BPW)
Blend the food at a speed of 15000 – 20000 rpm for not more than 2.5 minute or mix the stomacher for 20 seconds
Mix the food homogenate by shaking and pipette 1.0ml into a tube containing 9ml of the of the BPW, mix with a fresh pipette, and
From the first dilution, transfer with the same pipette
1.0ml to 2nd dilution tube containing 9ml of the BPW, mix with a fresh pipette, and
Repeat using a 3rd, 4th tube or more until the required numbers of dilutions are made.
Shake all dilution carefully.
Inoculate each of 3 tubes of LST broth (containing inverted Durham tubes) with 1.0ml of the food homogenate (1 in 10).
Carry out the same operation from the first (1 in 100) and the second 365