OGA Medium (Oxytetracycline Glucose Agar Base) (OGYE)

With a neutral pH, the oxytetracycline produces better results than when a low pH medium is used to inhibit bacterial growth. This medium inhibits the acidophilic organisms, Lactobacillus included.

Yeast extract is a source of vitamins, particularly of the B-group, essential for bacterial growth. Glucose is the fermentable carbohydrate as an energy source. Bacteriological agar is the solidifying agent.

Typical formula in g/L, adjusted and/or supplemented as required to meet performance criteria.

Preparation

Suspend 15 grams of the medium in 500 mL of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 10 minutes. Cool to 45-50 °C and aseptically add one vial of OGA Supplement (LC-6018). Homogenize gently and dispense into Petri dishes.

Instructions for use

For the enumeration and isolation of yeasts and molds in foodstuffs:

1. The pour plate method is recommended.
2. Inoculate 1 mL of 10⁻¹ diluted food sample and incubate at 20-25 °C.
3. Examine daily from the 2nd to the 6th day for the formation of aerial mycelia.
4. Count the number of colonies in plates where there are 50-100 colonies after 5 days.
5. Calculate the number of yeasts or molds per 1 g or 1 mL by multiplying the number of colonies by the dilution factor.

• American Public Health Association. Standard Methods for the Examination of Dairy Products, 13th Ed. APHA, Inc. New York, 1960.
• Thom and Raper, Manual of the Aspergilli 39:194.
• MOSSEL, D.A.A., KLEYNEN-SEMMELING, A.M.C., a. VENCENTE, H.M.: Oxytetracycline-Glucose-Yeast Extract Agar for selective enumeration of moulds and yeasts in foods and clinical material. - J. Appl. Bact., 33; 454-457 (1970).