Salmonella detection · Step 3 – selective isolation
SS Agar – selective plating medium for Salmonella and Shigella
Salmonella Shigella (SS) Agar is a selective and differential medium for the isolation of Salmonella and some Shigella species from food and clinical samples. It is a classic routine agar for enteric pathogens.
- Salmonella: colourless colonies with black centres
- Classic routine agar for enteric pathogens
- Dehydrated powder, 500 g bottle · COLO code PRO7493
How SS Agar works
Bile salts, brilliant green and sodium citrate inhibit Gram-positive bacteria and many coliforms. Lactose fermenters form pink to red colonies with neutral red, while Salmonella and Shigella do not ferment lactose and stay colourless. Thiosulfate and ferric citrate show hydrogen sulfide production as black colony centres.
Typical colony appearance
| Organism | Colonies |
| Salmonella | colourless, translucent, with black centres |
| Shigella | colourless to light pink |
| Lactose fermenters | pink to red |
Technical data
| Preparation | 56.5 g per litre of water; heat to boiling to dissolve; cool to about 50 °C and pour plates |
| Final pH | 7.0 ± 0.2 |
| Incubation | 35–37 °C, 24 h |
| Storage | Dry, dark place; close the cap tightly after use |
| Shelf life | 3 years unopened |
Applications and practical notes
SS Agar is a classic plating medium for Salmonella and Shigella in food and clinical microbiology. Typical applications include:
- meat, poultry and egg products
- dairy products
- water and environmental samples
- clinical stool samples
Working with SS Agar: Do not autoclave the medium and avoid overheating. SS Agar is strongly selective; it is best used together with a less inhibitory agar so that more sensitive strains are not missed.
Good practice with dehydrated media: keep the bottle tightly closed in a cool, dry place, weigh the powder quickly to avoid moisture uptake, and use fresh distilled or deionised water. Check the pH of each new batch after preparation and before use, and label prepared media with the date. Performance of each lot can be verified with reference strains according to ISO 11133, the standard for the preparation, production, storage and performance testing of culture media.
About the Salmonella culture method: the reference method for Salmonella in the food chain, ISO 6579-1, has four steps: non-selective pre-enrichment, selective enrichment in two broths, plating on two selective agars and confirmation of typical colonies. The FDA BAM Chapter 5 follows the same principle with media adapted to different food types. Rapid tests and identification kits shorten the time to result, but positive screening results are usually confirmed by the culture method. COLO.Science offers products for every step, so that one supplier covers the whole procedure.
Complete sets from one supplier: COLO.Science supplies culture media, supplements, rapid tests, identification kits and QC strains as complete sets for the method you follow. Send us your sample types and standards, and we will prepare an offer with the matching products and documentation.
SS Agar is supplied by COLO.Science in the pack sizes listed under Ordering information. For larger quantities, regular deliveries or method-specific sets that include SS Agar, please send us a request.
Where SS Agar fits in the Salmonella workflow
- Pre-enrichment – Buffered Peptone Water or Lactose Broth
- Selective enrichment – RVS Broth and MKTTn Broth
- Selective isolation – XLD Agar plus a second selective or chromogenic agar
- Confirmation – TSI, Lysine Iron Agar, Urea Agar, latex and biochemical identification
See the complete Salmonella set in the Microbiology Catalogue →
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| SS Agar, dehydrated | PRO7493 | 500 g |
| XLD Agar, dehydrated | PRO7437 | 500 g |
Product notice: preparation, storage conditions and shelf life are given on the label. Technical data on this page are for orientation; the label and the lot documentation apply. B2B prices are quoted net, excluding VAT.
Sales and technical support
COLO LabExperts
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Quotations and technical support for culture media and microbiology products across our international sales territory. B2B prices are net, excluding VAT.
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Need the complete set for your method?
Send the sample type, target organism and the standard you follow. COLO.Science will put together the media, supplements, QC strains and confirmation tests for the whole procedure.
