Vogel-Johnson Agar

 

Use: Vogel & Johnson Agar is a selective agar medium used for the detection of coagulase-positive, mannitol-positive Staphylococcus aureus strains in clinical specimens and foods or other materials of sanitary importance.

Description: Vogel & Johnson medium was developed by Vogel and Johnson as a modification of the Tellurite Glycine Agar Medium described earlier by Zabovitz, Evans, and Niven. Vogel and Johnson increased the mannitol content of the tellurite glycine agar and added a pH indicator, phenol red, to enable the detection of mannitol fermentation, a differentiating characteristic of most strains of Staphylococcus aureus. Coagulase-positive strains of S. aureus form characteristic black colonies on the medium due to the reduction of tellurite. Colonies of mannitol-fermenting strains will be surrounded by a yellow zone. The Association of Official Agricultural Chemists (AOAC) has recommended the medium for detection of S. aureus in foods. Due to the high selectivity of the medium and the sensitivity, Vogel-Johnson Medium may be used for the rapid detection of S. aureus in clinical specimens when the detection of the etiologic agent is of singular importance. Other microorganisms are easily distinguished by their inability to produce black colonies. Selective agents incorporated in the medium are glycine and lithium chloride, which inhibit growth of most other microorganisms. Potassium tellurite is added to the prepared medium. The tellurite salt is an inhibitory agent and is easily reduced by the coagulase-positive Staphylococci, leaving a black precipitate in the colony.

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