Laboratorios conda, s


CAT Nº: 1527
For the enumeration and isolation of yeasts and molds in food samples
Final pH 6.5 ± 0.2 at 25ºC

Suspend 15 grams of the medium in 500ml of distil ed water. Mix well and dissolve by heating with frequent agitation.
Boil for one minute until complete dissolution. Sterilize in autoclave at 121ºC for 10 minutes. Cool to 45-50ºC and
aseptical y add one vial of selective OGA Supplement (Cat. 6018), previously reconstituted in 5 ml of sterile distil ed
water. Homogenize gently and dispense into Petri dishes. The prepared medium should be stored at 8-15°C. The color is
The dehydrated medium should be homogeneous, free-flowing and beige in color. If there are any physical changes,
discard the medium.

(Composition: each vial for 500ml)
Oxytetracycline…………………………………………50 mg
* Alternatively, 0.05 grams of Gentamicin may be used as the antibiotic.
O.G.A. MEDIUM (Oxytetracycline Glucose Agar Base) is a selective medium, introduced by MOSSEL et al. and
recommended for the isolation and enumeration of yeasts and molds in foodstuffs, clinical specimens and cosmetics.
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 acidophilus organisms, Lactobacil us 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.
The pour plate method is recommended as indicated below:
Inoculate 1 ml of 10-1 diluted food sample and incubate at 20 - 25°C. Examine daily from the 2nd to the 6th day for the
formation of aerial mycelia.
Count numbers of colonies in plates where there are 50 - 100 colonies after 5 days. Calculate number of yeasts or
molds per 1 g or 1 ml by multiplying the number of colonies by the dilution factor.
(*) When examining fecal specimens from patients under tetracycline treatment, Enterobacteriaceae are not
adequately inhibited. Oxytetracycline should then be replaced by Gentamicin.

The fol owing results were obtained in the performance of the medium, with the O.G.A. Supplement (Cat. 6018) added,
from type cultures after incubation at a temperature of 20-25ºC and observed after 5 - 7 days.

American Public Health Association. Standard Methods for the Examination of Dairy Products, 1 3th Ed. APHA, Inc. New York, 1960.
Thom and Raper, Manual of the Aspergili 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).
Once opened keep powdered medium closed to avoid hydration.



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