Oxytetra Glucose Yeast Agar Base (OGYE Agar Base)
Selective enumeration of yeasts and moulds in foods (Mossel et al., 1970)
OGYE Agar is a neutral-pH selective medium for counting yeasts and moulds in foods, made selective by adding oxytetracycline (100 mg/L) instead of acid. Heat-stressed yeasts recover better on this medium than on acidified media, and the antibiotic suppresses bacteria, including lactobacilli.
Also known as: OGYE Agar, Oxytetracycline-Glucose-Yeast Extract Agar, OGY Agar.
Principle of the Medium
Yeast extract supplies vitamins and nitrogen, and glucose is the energy source for fungal growth. Oxytetracycline, a broad-spectrum antibiotic, inhibits most bacteria. Because selectivity comes from the antibiotic rather than low pH, yeasts that are injured by heat or processing are counted more completely than on acidified media.
Stressed yeast cells recover better than at low pH
Oxytetracycline suppresses bacteria, including lactobacilli
Three ingredients; clear medium for easy counting
Choosing a Yeast and Mould Medium
| Medium | Selective system | Best suited to |
|---|---|---|
| OGYE Agar (AS-1449) | Oxytetracycline, neutral pH | Most foods, dairy, heat-processed products |
| OGGY Agar | Oxytetracycline + gentamicin | Proteinaceous foods with heavy Gram-negative load |
| DRBC Agar | Chloramphenicol, dichloran, rose bengal | Foods with water activity above 0.95; restricts mould spreading |
| DG18 Agar | Chloramphenicol, dichloran, glycerol | Dry foods with water activity of 0.95 or below |
| Acidified Potato Dextrose Agar | Low pH (about 3.5) | Traditional method; may under-count stressed yeasts |
Comparable Products
| Supplier | Product | Relationship |
|---|---|---|
| AuSaMicS | OGYE Agar Base (AS-1449) | — |
| Oxoid (Thermo Fisher) | OGYE Agar Base (CM0545) | Same published formulation |
| Merck (Millipore) | OGYE Agar (1.05978) | Same published formulation |
| HiMedia | Oxytetra Glucose Yeast Agar Base (M639) | Same published formulation |
Based on published formulations. Trademarks belong to their respective owners.
Advantages and Limitations
Advantages
- ✓ Higher yeast counts than acidified media for stressed cells
- ✓ Inhibits lactobacilli, which grow on acidified media
- ✓ Well-established method, in use since 1970
- ✓ Clear medium for accurate counting
Limitations
- ▲ Protein-rich foods can inactivate oxytetracycline
- ▲ Incubation above 25 °C or beyond 5 days allows bacterial breakthrough
- ▲ Inoculum limit: no more than 1 mL of a 10⁻¹ dilution per plate
- ▲ No inhibitor of mould spreading; count early if moulds spread
Frequently Asked Questions
What is OGYE agar used for?
OGYE agar is used to count yeasts and moulds in foods. Oxytetracycline suppresses bacteria, while the neutral pH allows heat-stressed yeasts to recover.
Why does OGYE use oxytetracycline instead of a low pH?
Mossel and colleagues found that stressed yeast cells give higher counts on a neutral medium with a broad-spectrum antibiotic than on an acidified medium. Oxytetracycline also inhibits lactobacilli, which can grow on acidified media.
How much oxytetracycline is added?
100 mg per litre, added aseptically to the cooled base after autoclaving. Oxytetracycline is heat-sensitive and must not be autoclaved.
What temperature and time should I use?
Incubate aerobically at 22–25 °C for up to 5 days, examining after 3 days. Higher temperatures inactivate oxytetracycline faster and allow bacteria to break through.
When should I use a different medium?
For very proteinaceous foods or samples heavily contaminated with Gram-negative bacteria, add gentamicin (OGGY) or use DRBC agar. For low water activity foods, use DG18 agar.
Typical Formula (g/L)
Formula may be adjusted to meet performance requirements.
Test Procedure
Plating: Use pour plates or spread plates. Add no more than 1 mL of a 10⁻¹ food dilution per plate, so the food does not overwhelm the antibiotic.
Incubation: Aerobically at 22–25 °C for up to 5 days. Examine after 3 days, and count earlier if moulds spread.
Counting: Count yeast and mould colonies separately if required, and report as CFU per g or mL.
Related Standards (for user reference)
ISO 6611 | IDF 94 (milk and milk products) describes a yeast extract–glucose–oxytetracycline agar. ISO 21527-1 and ISO 21527-2 (foods) specify DRBC and DG18 agar.
References
- Mossel DAA, Kleynen-Semmeling AMC, Vincentie HM, Beerens H, Catsaras M. Oxytetracycline-glucose-yeast extract agar for selective enumeration of moulds and yeasts in foods and clinical material. J Appl Bacteriol. 1970;33:454–457.
- Mossel DAA, Visser M, Mengerink WHJ. A comparison of media for the enumeration of moulds and yeasts in foods and beverages. Lab Pract. 1962;11:109–112.
- Pitt JI, Hocking AD. Fungi and Food Spoilage. 3rd ed. Springer; 2009.
- Salfinger Y, Tortorello ML, eds. Compendium of Methods for the Microbiological Examination of Foods. 5th ed. APHA; 2015.
Quality Control
Recommended Control Strains (with oxytetracycline, 25 °C, 3–5 days)
Safety
The base is not classified as hazardous under the GHS and is not Dangerous Goods for transport. Oxytetracycline is a separate product with its own SDS. Treat inoculated plates as potentially infectious and autoclave before disposal. The full SDS is available for every lot.
Storage
Dehydrated base: Store at 15–25 °C in a dry place with the container tightly closed. The powder is hygroscopic. Use before the expiry date on the label.
Prepared plates (with oxytetracycline): Store at 2–8 °C, protected from light. Validate the use period in your laboratory.