Aim
Salt Meat Broth is used as an enrichment medium for staphylococci isolation from severely contaminated specimens.
Principle
Salt Meat Broth, an enrichment media used to isolate halophilic staphylococci in contaminated samples like faeces and blood. This is especially useful in cases of food poisoning. It is sensitive because it can detect low levels of staphylococci even in samples with high heterogeneous microbial populations. Because of high levels of sodium chloride, the medium is highly selective for staphylococci. Staphylococcus Aureus can tolerate high levels of sodium chloride, which inhibits most bacteria. Salt Meat Broth is also useful for cultivating some halophilic micrococci that are associated with raw salt and hides. This medium is not suitable for testing for coagulase production. Therefore, they should first be subcultured on Blood Agar. The essential nutrients for bacterial metabolism are provided by the peptic digest of animal tissue, and beef extract. Sodium chloride helps maintain osmotic equilibrium.
Salt Meat Broth Composition
| Ingredients | Gms / Litre |
| Beef extract | 10 |
| Peptic digest of animal tissue | 10 |
| Neutral ox-heart tissue | 30 |
| Sodium chloride | 100 |
| Final pH ( at 25°C) | 7.6±0.2 |
Salt Meat Broth Preparation
- Take 15 grams and mix it with 100 ml of distilled water.
- Allow to soak for five minutes.
- If necessary, heat the medium to dissolve it completely.
- Use a test tube measuring 5/8 inches in diameter to disperse and dispense the mixture.
- For 15 minutes, sterilize by using an autoclave at 15 lbs pressure (121degC).
Procedure for Staphylococcus aureus isolation
- After incubation at 35deg-37OC for 24 to 48 hours, discrete colonies can be obtained by plating a small amount of the liquid culture onto Mannitol Salt Agar CM85 and Staphylococcus Medium.
Important
- This medium is not recommended for enrichment of foods with staphylococci. If stressed organisms are not first incubated with a non-selective medium (e.g., broth), productivity is likely to suffer. To allow for resuscitation, you can use Soya broth made from Tryptone Soya.
- This medium can be used to cultivate some of the halophilic micrococci that are associated with raw salt and hides.
- It is important to note that staphylococci grown on this medium can’t be tested for coagulase activity. They should first be subcultured in a medium with less salt. This is why Blood Agar Base (CM55) is recommended.
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 25°C
Quality Control
- Positive control: Staphylococcus aureus ATCC” 25923
- Negative control: Escherichia coli ATCC” 25922
