OXYTETRACYCLIN GLUC YEAST EXT 500g

Specifications

Description

Oxytetracycline-Glucose-Yeast Extract Agar is recommended for the selection and enumeration of yeasts and moulds from foodstuffs^1,2. The medium using oxytetracycline as the selective agent is based on the formulation developed by Mossel et al.³, who stated that the use of this antibiotic in a medium with a neutral pH gave increased counts of yeasts and moulds from a variety of foodstuffs compared with media which relied on a low pH to suppress bacterial growth. Physically stressed yeast cells give higher counts on media which depend upon broad-spectrum antibiotics rather than a low pH for selectivity⁴. In earlier work Mossel⁵ found that Glucose Yeast Extract Agar was as favourable a basal medium as `Mycophil’ Agar later recommended by Sharf<sup>6</sup>. Addition of the oxytetracycline was found to make the Glucose Yeast Extract Agar more selective than `Mycophil’ Agar by inhibiting the growth of lactobacilli, most of which grow at the acid pH of the latter medium.

The choice of a suitable medium for enumeration of yeasts and moulds is greatly dependent on the nature of the foodstuffs under investigation and the organisms that occur on them⁷. Oxytetracycline-Glucose-Yeast Extract Agar remains bacteriostatic when inoculated with not greater than 1ml of a 10^-1 dilution of foods and subsequently incubated for not greater than 5 days at 25°C as is the customary practice in food mycology².
For isolation of psychrotrophic yeasts from chilled proteinaceous foods a combination of oxytetracycline and gentamicin is effective⁸.

Very proteinaceous foods and the higher incubation temperatures around 35°C required for some organisms will inactivate oxytetracycline allowing growth of Gram positive and Gram negative rods. For such applications Rose-Bengal Chloramphenicol Agar (CM0549) may be substituted or Dichloran-Glycerol (DG18) Agar Base (CM0729).