Marine Oxidation Fermentation HiVeg™ Medium (MOF HiVeg™ Medium)

Principle And Interpretation

Some organisms metabolize glucose oxidatively and others ferment glucose fermentatively when the hydrogen acceptor is not oxygen. Such organisms can be differentiated based on the Oxidation Fermentation Test. This test is also known as the "oxferm" test. MOF medium is a modified version of the formula originally developed by Leifson (1); used for differentiating oxidative and fermentative carbohydrate metabolizing marine bacteria. The marine environment of the oceans illustrates a different view of microbial populations in water. In the high salt concentration of ocean water, halophillic or salt- loving microorganisms survive. In addition, the organisms must be psychrophilic since it is very cold below the surface. Those at bottom must also withstand great pressure and are therefore barophilic or pressure loving (2). HiVeg™ hydrolysate and yeast extract in the medium supply the necessary nitrogenous nutrients including amino acids, vitamins etc. The mineral content of this medium is equivalent to one-half that of seawater (1). It contains a variety of salts found in seawater, which not only makes the medium suitable for marine bacteria but also buffers the medium. Phenol red is the pH indicator in the medium. MOF HiVeg™ Medium is prepared by using vegetable peptones in place of animal based peptones which make the media free of BSE/TSE risks.For differentiating the fermentation and oxidation of carbohydrates, inoculate two tubes of medium containing carbohydrate with each culture to be tested. Cover one medium tube of each culture with sterile melted petrolatum to form a layer of about one inch in height. Carbohydrate -fermenting marine bacteria change the colour of the medium in both the tubes (covered and uncovered) from red to yellow whereas carbohydrate-oxidizing marine bacteria change the colour of the medium from red to yellow only in the uncovered (open) tube. Marine bacteria that are neither oxidative nor fermentation do not exhibit any change in the covered medium and exhibit an alkaline (red to deep pink) reaction in the uncovered medium. Gas production is detected as splitting or displacement of agar or formation of small bubbles. Motile organisms form a diffuse zone of growth originating from the line of inoculation. Non-motile organisms grow along the line of inoculation.