Tryptone Soya Broth for the enrichment of Staph. aureus

Aim

Supplemented with sodium pyruvate and sodium chloride, tryptone soya soup can be used for selective enrichment of Staphylococcus Aureus. 

Principle

Tryptone Soya soup is a nutritious medium that can be used to grow bacteria and fungi. It contains a combination of hydrolysates from soya and casein, which provide a broad range of essential nutrients that can be used to resuscitate cells suffering from sub-lethal damage.

Tryptone Soya soup is versatile and can be used in a variety of applications, including in clinical microbiology and pharmaceuticals. Its ability to stimulate growth from very small numbers of organisms is why it is listed in the United States Pharmacopeia as Soybean Casein Digest medium USP. This allows for sterilization testing of pharmaceutical products. It is used in food microbiology as a base for a variety of media for selective enrichment Escherichiacoli 0 1572. Another American method uses Tryptone Soya broth to repair and enrich Staphylococcus Aureus in processed foods.

After incubation in nonselective Tryptone Soya soup to allow damaged cells to heal, sodium chloride is added to the culture for selective enrichment. A selective enrichment procedure is used to detect small amounts of Staph in Tryptone Soya soup broth. Raw food ingredients, and foods that are not expected to have a large number of competing species may contain aureus.

Tryptone Soya Broth composition

Formula	grams/litre
Pancreatic digest of casein	17
Papaic digest of soybean meal	3
Sodium chloride	5
Dibasic potassium phosphate	2.5
Glucose	2.5

pH 7.3 ± 0.2

Tryptone Soya Broth Preparation

1. Mix 300 g in 1 liter distilled water, and then distribute the mixture into your final containers.
2. For 15 minutes, sterilize it by using an autoclave at 121 oc

Procedure for use of Tryptone Soya Broth

Repair-selective enrichment procedure for Staph. aureus in foods

This is recommended to test processed foods that are more likely to have small amounts of damaged cells.

1. 50 ml of the dilute prepared sample
2. 50ml double-strength Tryptone Soya soup
3. For 3 hours, incubate at 35-37degC
4. Mix 100ml single-strength Tryptone Soya soup containing 20% sodium chloride.
5. Incubate for 24 hours at 35deg-3JOC
6. To make duplicate plates from Baird-Parker, add 0.1 ml enrichment culture. Spread to form isolated colonies Incubate 46 +/- 2 hours at 35deg-3JOC

Selective enrichment procedure for Staph. aureus in foods

This is a good procedure to detect low levels of Staph. Aureus can be found in foods that contain high levels of unprocessed or raw ingredients.

1. Decimal dilutions of prepared sample* (1 ml + 10 ml Tryptone Soya broth+ 10% NaCI + 1% sodium pyruvate)
2. Incubate for 48 hours +/- 2 hours at 35deg/37degC
3. Each growth-positive tube should be subcultured to Baird Parker agar
4. Incubate for 48 hours +/- 2 hours at 35degC-37degC
5. The maximum possible dilution should be sufficient to not yield growth.

Quality Control

• Positive control: Streptococcus pneumoniae ATCC” 6303, Staphylococcus aureus ATCC” 25923
• Negative control: Uninoculated medium

Storage Conditions and Shelf Life

• Keep the dehydrated medium at 25°C, and use it before the expiry date printed on the label.
• Keep the prepared medium at room temperatures.