You are presented with an agar medium containing the antibiotic vancomycin, the carbohydrate sugar trehalose, and the pH indicator phenol red. What is the accurate classification of this medium?

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Examining the scenario: an agar medium containing vancomycin, trehalose, and a pH indicator (phenol red). Each component provides clues about what the medium is designed to do.
Option a: Enriched medium. Enriched media are designed to support the growth of fastidious organisms by providing additional nutrients. The presence of vancomycin and trehalose does not indicate enrichment alone; vancomycin is an inhibitory agent, and trehalose is a fermentable sugar. If the medium were simply enriched, there would be no emphasis on selective inhibition of competing organisms or on differential reactions via a pH indicator.
Option b: General-purpose medium. General-purpose media support the growth of a broad range of non-fastidious organisms and typically lack selective agents or differential indicators. Since this medium contains antibiotic vancomycin, it introduces selectivity by inhibiting some organisms, which excludes it from being a plain general-purpose medium.
Option c: Selective and differential medium. This option fits well: vancomycin serves as a selective agent, inhibiting certain bacteria and allowing others to grow, while trehalose can act as a fermentable carbohydrate, enabling metabolic differentiation that may be reported by the pH indicator phenol red through color change. The combination of an inhibitory substance plus a detectable metabolic product aligns with both selectivity and differential capability.
Option d: Differential medium. A differential medium reveals differences among organisms (often via a color change from a pH indicator) but does not necessarily include a selective agent like an antibiotic to inhibit some species. In this case, vancomycin provides selectivity, so while the medium is differential, the presence of the antibiotic adds a selective component beyond a purely differential description.
In summary, the kit of components suggests the medium is designed to both differentiate organisms that can metabolize trehalose (reflected by the pH indicator) and suppress growth of non-susceptible bacteria via vancomycin, which is characteristic of a selective and differential medium.

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You are presented with an agar medium containing the antibiotic vancomycin, the carbohydrate sugar trehalose, and the pH indicator phenol red. What is the accurate classification of this medium?

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