Microbiology culture media
A microbiology culture medium is a nutrient formulation that allows microorganisms to be grown, enumerated, isolated or identified from a clinical, food, environmental or industrial sample. In the CABRU catalogue the range is that of Condalab: 1,157 references in total, of which 1,031 are classified as microbiology, 122 as molecular biology and 4 as cell culture. Among the microbiology ones, 427 are agars, 199 broths, 80 peptones and extracts, 51 supplements and 35 chromogenic media; 283 carry a reference to an ISO method in their name.
Selective, differential, chromogenic: what changes
A general-purpose medium feeds whatever grows and serves to resuscitate or enrich. A selective medium adds inhibitors — bile salts, antibiotics, crystal violet, high salt concentrations — that hold back non-target flora: it gains specificity and loses part of a stressed target, which is why standard methods often place an enrichment step before selection. A differential medium does not inhibit but reveals: a pH indicator or a substrate exposes a metabolic property, and colonies are told apart by colour or halo. A chromogenic medium is the modern form of the differential one: a colourless substrate bound to a chromophore is cleaved by a specific enzyme and the colour stays inside the colony. Colour, however, gives a presumptive identification, not a confirmation.
Dehydrated or ready-to-use: who runs the performance test
The difference between formats is not only convenience: it moves the responsibility for quality control. The reference standard is ISO 11133, which covers preparation, production, storage and performance testing of media for food, feed and water, and calls for three checks — productivity, selectivity, specificity.
| Format | References in catalogue | Who tests the batch | When it suits |
|---|---|---|---|
| Dehydrated powdered medium | 463 in the 500 g size | The laboratory that prepares it | High volumes, formulations to be adapted |
| Ready-to-use plates | 144 | The manufacturer, with a batch certificate | Few samples, no in-house preparation |
| Ready-to-use tubes and bottles | 75 | The manufacturer | Transport media, enrichments, bottle counts |
| Selective supplements | 51 | The manufacturer, paired with the base | Heat-labile additives, added after sterilisation |
Storage and searching the catalogue
Dehydrated media are hygroscopic: they are kept in the original container tightly closed, in a dry place away from light, and browning or caking of the powder is a reason to discard, not to reduce the weighed amount. A deeper treatment of chromogenic media and the ISO methods that call for them is in the chromogenic culture media guide. References can be browsed in the product catalogue filtering by company: for an enquiry it helps to state matrix, reference method and required format.