Peptone and culture media glossary
Peptone, yeast extract, amino nitrogen, selective medium, COA: what these terms actually mean, each in one plain paragraph.
- Peptone
A mixture of peptides and amino acids produced by enzymatic or acid hydrolysis of protein, the principal nitrogen source in culture media. Classified by raw material (casein, meat, soy, yeast, wheat) and by degree of hydrolysis (amino nitrogen ratio).
Related:TryptoneYeast extractAmino nitrogen / total nitrogen (AN/TN)
- Tryptone
Casein hydrolysed with pancreatic enzymes; a complete amino-acid profile rich in tryptophan, the nitrogen source of LB, TSB and other standard media. Also called pancreatic digest of casein.
Related:PeptoneCasamino acids
- Casamino acids
Casein completely hydrolysed with hydrochloric acid, consisting almost entirely of free amino acids with the highest amino-nitrogen ratio; tryptophan is destroyed in acid hydrolysis.
- Yeast extract
The soluble fraction of autolysed yeast cells, concentrated and dried; rich in B vitamins, nucleotides and free amino acids, the most widely used source of growth factors.
Related:Yeast peptonePeptone
- Yeast peptone
Yeast protein hydrolysed with enzymes; more peptides and fewer vitamins than yeast extract, positioned between a peptone and an extract.
Related:Yeast extract
- Soy peptone
A plant peptone from soybean protein hydrolysed with papain or similar enzymes; contains carbohydrate, is the second nitrogen source in TSB and is common in lactic acid bacteria and plant-based processes. Also called papaic digest of soybean meal.
- Beef extract
A paste or powder concentrated from boiled beef, supplying water-soluble vitamins, salts and flavour compounds; common in traditional formulations such as Nutrient Broth and MRS.
Related:Peptone
- Amino nitrogen / total nitrogen (AN/TN)
The share of amino nitrogen in total nitrogen, indicating the degree of hydrolysis. A high ratio means more small molecules that cells use directly; a low ratio means slower nitrogen release.
Related:PeptoneTotal nitrogen
- Total nitrogen
Nitrogen content by the Kjeldahl method; multiplied by 6.25 it approximates crude protein. Peptones typically contain 10 to 14%.
- Dehydrated culture media (DCM)
All components of a formulation pre-blended as a powder; the user adds water at the stated amount per litre and sterilises. Saves weighing individual ingredients and gives batch-to-batch consistency.
Related:AgarSelective medium
- Agar
A polysaccharide extracted from red algae that dissolves on heating and gels on cooling, the gelling agent of solid media. The usual concentration is about 15 g per litre; gel strength varies by grade.
Related:Dehydrated culture media (DCM)
- Selective medium
A medium containing inhibitors (bile salts, dyes, antibiotics, high salt) that suppress organisms other than the target, such as MacConkey, Baird-Parker and TCBS.
Related:Differential mediumEnrichment
- Differential medium
A medium with indicators or substrates that make organisms look different according to their metabolism, for example lactose with neutral red turning lactose-fermenting colonies red.
Related:Selective medium
- Enrichment
Growing a small or injured target population in a broth to a detectable number before plating on selective agar. Buffered Peptone Water in Salmonella testing is the classic pre-enrichment.
Related:Selective medium
- Cultural response
Inoculating the medium with reference strains (ATCC and similar) to confirm growth, inhibition or colour reactions as expected; the performance test for each batch before release.
Related:Certificate of Analysis (COA)
- Certificate of Analysis (COA)
The actual test results of one batch before release, compared with the specification; used for incoming inspection and traceability.
- Technical Data Sheet (TDS)
The product's formulation, specification ranges, preparation, cultural response and storage conditions; also called the specification sheet.
Related:Certificate of Analysis (COA)Safety Data Sheet (SDS)
- Safety Data Sheet (SDS)
A GHS-format document giving hazard classification, handling, storage and first-aid information.
Related:Technical Data Sheet (TDS)
- Halal certification
Audit by a certification body of raw material origin, process and cross-contamination control to confirm compliance with Islamic law. Halal versions of media have the same formulation and performance; the difference is in sourcing and process documentation.
Related:Animal-free (animal origin free)
- Animal-free (animal origin free)
No animal-derived raw materials, enzymes or processing aids, used in vaccine, cell culture and plant-based food processes.
Related:Soy peptoneHalal certification
- Non-GMO
Plant raw materials from non-genetically modified crops, supported by supplier declarations kept on file.
Related:Animal-free (animal origin free)
- Ultrafiltration (UF)
Membrane filtration that removes large molecules, giving peptones and yeast extracts a narrower molecular-weight distribution and clearer solutions; common in cell-culture-grade products.
Related:Peptone
- Food grade
Media or peptones made from food-grade raw materials under a food safety management system (ISO 22000), suitable for fermented products that are consumed directly.
Related:Halal certification
- ATCC reference strains
Numbered strains from the American Type Culture Collection used as the benchmark in cultural response testing, for example Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923.
Related:Cultural response
- Most probable number (MPN)
A statistical estimate of cell numbers from the pattern of positive tubes in serial dilutions, used in coliform testing with Lauryl Tryptose Broth and EC Broth.
Related:Enrichment