Enterobacteriaceae · Differentiation
Simmons Citrate Agar – citrate utilisation test
Simmons Citrate Agar is used to differentiate Gram-negative enteric bacteria by their ability to use citrate as the only carbon source, for example as the citrate test of the IMViC series.
- Citrate as the only carbon source
- Blue colour = positive
- Prepared as slants
How Simmons Citrate Agar works
Organisms that use citrate also use ammonium salts as the nitrogen source and make the medium alkaline, so the bromothymol blue indicator turns from green to blue. Organisms that cannot use citrate do not grow and the medium stays green.
Typical results
| Organism | Reaction |
| Klebsiella pneumoniae | Growth, medium turns blue |
| Shigella sonnei | No colour change (green) |
Technical data
| Preparation | 27.3 g/L; boil to dissolve, dispense into tubes, autoclave 121 °C 15 min; set as slants |
| Final pH | 6.8 ± 0.2 |
| Incubation | 35–37 °C, 24 h |
| Storage | Dry, dark place; keep the container tightly closed |
| Shelf life | 3 years |
Applications and practical notes
Enterobacteriaceae are counted as hygiene indicators according to ISO 21528-2 and differentiated with classic biochemical media. Typical applications include:
- Food and feed hygiene control
- Differentiation of Gram-negative isolates
- Pharmaceutical non-sterile products
- Training and reference laboratories
Working with Simmons Citrate Agar: Inoculate the slant lightly from a single colony with a needle, so that no nutrients are carried over, and incubate with the cap loose.
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 Enterobacteriaceae methods: Enterobacteriaceae are hygiene indicators in food and feed. ISO 21528-2 counts them on Violet Red Bile Glucose Agar, and ISO 21528-1 detects them after enrichment in Enterobacteria Enrichment Broth Mossel. Typical colonies are confirmed as oxidase-negative and glucose-fermenting. The European Pharmacopoeia and USP use the same broth and agar for bile-tolerant Gram-negative bacteria in non-sterile products. Kligler Iron Agar, Simmons Citrate Agar and identification kits are used to differentiate isolates. COLO.Science offers media, identification kits and QC strains for these steps.
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.
Simmons Citrate 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 Simmons Citrate Agar, please send us a request. With every delivery of Simmons Citrate Agar you receive the lot number and expiry date, and on request we send the available documentation for Simmons Citrate Agar.
Where Simmons Citrate Agar fits in Enterobacteriaceae testing
- Enrichment – Enterobacteria Enrichment Broth Mossel
- Enumeration and isolation – Violet Red Bile Glucose Agar
- Confirmation – oxidase test and glucose fermentation; Kligler Iron Agar, TSI and Simmons Citrate Agar for differentiation
- Identification – Enterobacteriaceae biochemical identification kit
See all Enterobacteriaceae products in the Microbiology Catalogue →
Ordering information
| Product | COLO code | Pack |
|---|---|---|
| Simmons Citrate Agar | PRO7492 | 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
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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.
