Salmonella Shigella (SS) Agar is a medium for the isolation, cultivation and differentiation of Salmonella spp.
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In this article, we will explore some important information about Salmonella Shigella (SS) Agar.
Keep reading to find out more.
What Is Salmonella Shigella (SS) Agar?
Salmonella Shigella (SS) Agar is a differential selective media used for the isolation of Salmonella and some Shigella species from suspected foods and pathological specimens.
Salmonella Shigella (SS) Agar is recommended for testing clinical specimens and food for the presence of Salmonella spp. and Shigella spp.
The Composition Of Salmonella Shigella (SS) Agar
Let’s take a closer look at the composition of Salmonella Shigella Agar to gain a better understanding of what goes into it.
Ingredients Gms / Liter
- Agar 13.5
- Lactose 10.0
- Sodium thiosulphate 8.5
- Bile salts mixture 8.5
- Sodium citrate 8.5
- Proteose peptone 5.0
- Ferric citrate 1.0
- Brilliant green 0.00033
- Neutral red 0.025
- Distilled water: 1000 ml
Final pH ( at 25°C) 7.0±0.2
The Principle Of Salmonella Shigella (SS) Agar
- Including Sodium Citrate, Bile Salts, as well as Brilliant Green allow Salmonella to grow and inhibit gram-positive, coliform organisms and inhibit swarming Proteus spp.
- Enzymatic Digest of Animal Tissue, Beef Extract, and Enzymatic Digest of Casein provide sources of carbon, nitrogen, and the necessary vitamins required for organism growth.
- The carbohydrate, lactose, is in Salmonella Shigella Agar.
- Ferric Citrate as well as Thiosulfate permit detection of hydrogen sulfide by the production of colonies that have black coloring in the center.
- Neutral red turns red when exposed to an acidic pH, exhibiting that fermentation has happened.
Uses Of Salmonella Shigella (SS) Agar
There are various uses of Salmonella Shigella (SS) Agar, which include:
- A medium for the isolation of Salmonella and some Shigella species from clinical and non-clinical specimens.
- The differentiation of lactose and non-lactose-fermenters from clinical specimens, suspected foods, and other samples.
On the other hand, Salmonella Shigella (SS) Agar is not:
- Recommended for the isolation of Shigella.
The Preparation Of Salmonella Shigella Agar
- Step One – Place 60.0 grams of Salmonella Shigella Agar in 1000 ml of distilled water.
- Step Two – You will then need to boil the water in order to entirely dissolve the medium.
- Step Three – Do not overheat or autoclave. Overheating may destroy the selectivity of the medium.
- Step Four – Allow the mixture to cool to 122°F (or 50°C).
- Step Five – Next, you will need to stir the mixture until well combined and begin pouring the mixture into sterile petri plates and allow the agar to solidify.
- Step Six – Last, but by no means least, store the petri plates in the refrigerator at 35.6°F to 46.4°F (or 2 to 8°C)
Test Procedure For Salmonella Shigella (SS) Agar
- Step One – Allow the plates to warm at room temperature, and allow the agar surface to dry completely before you begin the inoculation process.
- Step Two – Handle the Salmonella-Shigella (SS) Agar plates carefully.
- Step Three – You will need to inoculate and streak the specimen as soon as possible after it has been collected. If the specimen in question is on a swap, roll it over an area of the agar surface. Following this, you will need to streak for isolation with a sterile loop.
- Step Four – Incubate aerobically plates at 35 ± 2°C for 18 to 24 hours.
Result Interpretation Of Salmonella Shigella Agar
Salmonella will produce hydrogen sulfide (H2S) gas, but won’t ferment lactose. Bearing this in mind, the bacterial colonies will be colorless with black coloring in the center.
Shigella won’t produce hydrogen sulfide gas, and won’t ferment lactose. As a result, the colonies won’t have any color at all.
Coliform bacteria, like E. coli, will ferment the lactose in the media. As a result, there will be bacterial growth with a pink color to observe.
- Salmonella typhimurium ATCC 14028 – Colorless colonies with a black center
- Salmonella typhi ATCC 6539 – Colorless colonies with a black center
- Salmonella enteriditis ATCC 13076 – Colorless colonies with a black center
- Shigella flexneri ATCC 12022 – Colorless colonies
- Escherichia coli ATCC 25922 – Inhibited
- Enterococcus faecalis ATCC 19433 – Inhibited
- Enterobacter aerogenes ATCC 13048 – Partially inhibited. Cream-pink
What Are The Limitations Associated With Salmonella Shigella Agar?
There are several limitations of Salmonella Shigella Agar.
These include but are not limited to:
- Salmonella Shigella Agar is for laboratory use only.
- The bile salts have the potential to crystallize. They have an appearance of small, puffy balls in the medium. However, despite their presence, they won’t impact the performance of the medium.
- The Brilliant Green in the medium makes it selective. As a result, it has been known to inhibit some Shigella species from growing.
- Non-pathogenic organisms have the potential to grow on Salmonella Shigella.
What Is The Storage And Shelf Life Of Salmonella Shigella (SS) Agar?
Generally speaking, Salmonella Shigella (SS) Agar needs to be stored at 35.6°F to 46.4°F (or 2 to 8°C) and away from direct sunlight.
This comes down to the fact that this product is sensitive to light and temperatures, and therefore needs to be protected from moisture, excessive exposure to heat, exposure to light, as well as freezing.
When it comes to storing, the prepared culture media will last for a minimum of a week when it is kept in the refrigerator.
That being said, no media that has shown any signs of deterioration such as cracking, shrinking, or discoloration should be used.
Precautions Of Salmonella Shigella (SS) Agar
There are a few precautions that you should take when it comes to dealing with Salmonella Shigella (SS) Agar. These include but are not limited to:
Salmonella Shigella might contain animal components.
As the sanitary state of the animal doesn’t guarantee that the product doesn’t contain transmissible pathogenic agents, the product needs to be handled and treated as if it is potentially infectious.
The product should not be allowed to come into contact with your skin, and should never be inhaled or ingested.
This product should only be used only by highly trained and qualified laboratory personnel.
As a result, all laboratory specimens need to be treated as if they are infectious and handled according to standard precautions.
We have now reached the end of this article on Salmonella Shigella (SS) Agar.
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