TSYEB Broth (Tryptone Soy Yeast Extract Broth) ISO

Casein peptone and soy peptone provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is a source of vitamins, particularly of the B-group, essential for bacterial growth. Glucose is the fermentable carbohydrate providing carbon and energy. Dipotassium phosphate acts as a buffer system. Sodium chloride supplies essential electrolytes for transport and osmotic balance.

Preparation

Suspend 36 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

Instructions for use

Motility test for confirmation of Listeria spp.:

1. Take an isolated colony and suspend it in a tube containing TSYEB.
2. Incubate at 25 °C for 8 to 24 hours until the medium turns cloudy.
3. Take a drop onto a clean glass slide for a microscope, place the cover slip on top and examine it under the microscope.
4. Listeria spp. appears as slim, short rods with tumbling motility.
5. Cultures grown above 25 °C may not exhibit this motility. They should always be compared against a known culture.
6. Cocci, large rods or rods with rapid swimming motility are not Listeria spp.

Carbohydrate test for the confirmation of Listeria monocytogenes:

1. Inoculate each of the carbohydrate broths with a TSYEB broth culture.
2. Incubate at 35 ± 2 °C for 18-48 hours.
3. Positive reaction is indicated by yellow color (aldehyde formation).

• ISO 11290-1:1999 Microbiology of food and animal feeding stuffs. Horizontal method for the detection and enumeration of Listeria monocytogenes. Part 1: Detection method. Amendment 1: Modification of the isolation media and the haemolysis test and inclusion of precision data.