What organism is identified by producing orange, waxy colonies and showing partial acid-fast staining?

The organism that is identified by producing orange, waxy colonies and showing partial acid-fast staining is Nocardia spp. This genus is known for its unique morphological characteristics and staining properties. Nocardia species exhibit filamentous growth and can form colonies that appear orange and waxy due to their mycolic acid-rich cell walls, which is a distinguishing feature of acid-fast organisms.

The partial acid-fastness of Nocardia is attributed to the presence of mycolic acids, which can retain certain dyes even after acid-alcohol decolorization during the staining process. This characteristic helps differentiate Nocardia from other filamentous bacteria that do not exhibit such acid-fast characteristics.

In contrast, Rhodococcus species also show some degree of acid-fastness but are generally not described as producing the same orange, waxy colonies. Actinomadura and Streptomyces, while similar in being filamentous and related to soil organisms, do not possess the same level of acid-fastness and do not typically produce the distinctive orange colonies observed with Nocardia. Understanding these specific traits helps us effectively identify and differentiate these organisms in microbiological studies.