OF Medium w/1% Dextrose

Determine oxidative and fermentative metabolism of glucose by gram-negative bacilli using Thermo Scientific™ Remel™ OF Medium w/1% Dextrose (Hugh-Liefson). Hugh and Leifson first reported that microorganisms which utilize carbohydrates oxidatively produce only a minimal amount of acid¹. Oxidative-Fermentative (OF) Medium was developed with a ratio of peptone to carbohydrate that minimized the formation of alkaline by-products and enhanced acid production by oxidative organisms. OF Medium is especially suitable for determining the carbohydrate metabolic pathway of gram-negative bacilli².

Typical fermentation media contain approximately 2% peptone and 1% carbohydrate. In media containing high concentrations of peptones, oxidative microorganisms produce alkaline by-products in quantities that neutralize the acid produced from carbohydrate metabolism.

OF Medium is a semisolid medium with a low peptone to carbohydrate ratio that contains the pH indicator bromthymol blue. Organisms which metabolize carbohydrate in OF medium produce acid in quantities sufficient to prevent its neutralization by alkaline peptone by-products.

• Ready to use – Convenience of prepared media
• Uses 4 mL of 1% Dextrose as carbohydrate source
• Easy to interpret – Color change from green to yellow indicates positive test for acid production.
  When testing for motility, growth diffused away from stab line of inoculation indicates a positive test whereas growth confined to stab line indicates negative test.
  Acid production in the open tube (without mineral oil overlay) indicates oxidative metabolism whereas acid production in both (with and without mineral oil overlay) tubes indicates fermentative metabolism

OF Medium with Dextrose uses 4 mL of 1% dextrose as a fermentable carbohydrate. The medium contains casein peptone as the substrate and bromthymol blue as the pH indicator. Dipotassium phosphate promotes fermentation and also serves as a buffer. Agar allows for detection of motility and aids in even distribution of acid produced at the surface of the medium.

Dextrose is routinely used in OF Medium; however, some organisms may be unable to metabolize dextrose but can utilize other carbohydrates. Organisms that only oxidise glucose will not ferment any other carbohydrate¹. Therefore, when testing with other carbohydrates, the mineral oil overlay tube may be omitted.

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