Rhodococcus equi is distinguished by pink pigmentation on culture media and was formerly classified in which genus?

Rhodococcus equi is distinguished by pink pigmentation on culture media and was formerly classified in which genus?

• A. Corynebacterium
• B. Nocardia
• C. Mycobacterium
• D. Actinomyces

Answer: (B)

Pink pigment production is a clue that helps separate Rhodococcus from other similar Gram-positive rods. This organism was historically placed with the corynebacteria and named Corynebacterium equi, reflecting its resemblance to Corynebacterium in shape and staining. As taxonomic understanding improved with genetic and chemotaxonomic data, it was reclassified into its own genus, Rhodococcus, to reflect its distinct lineage. The other genera listed differ in pigment patterns, cell wall traits, or taxonomic placement, so they don’t fit the historical classification. Thus, it was formerly classified under Corynebacterium.

Pink pigment production is a clue that helps separate Rhodococcus from other similar Gram-positive rods. This organism was historically placed with the corynebacteria and named Corynebacterium equi, reflecting its resemblance to Corynebacterium in shape and staining. As taxonomic understanding improved with genetic and chemotaxonomic data, it was reclassified into its own genus, Rhodococcus, to reflect its distinct lineage. The other genera listed differ in pigment patterns, cell wall traits, or taxonomic placement, so they don’t fit the historical classification. Thus, it was formerly classified under Corynebacterium.