Which organism is a Gram-positive, branching rod that is partially acid-fast and shows breadcrumb-like colonies?

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Multiple Choice

Which organism is a Gram-positive, branching rod that is partially acid-fast and shows breadcrumb-like colonies?

When you see a Gram-positive organism that forms branching filaments and stains only weakly acid-fast, with colonies described as dry, chalky, and crumbly—often called breadcrumb-like—you’re in the realm of Nocardia. These features come together because Nocardia is an aerobic actinomycete with cell walls rich in mycolic acids, which gives it partial acid-fastness (not as strong as Mycobacterium). The branching filaments reflect its filamentous, mold-like appearance, yet it is a bacterium, not a fungus. In culture, the colonies tend to look crumbly and bread-crumb-like, aiding its recognition. Other Gram-positive rods don’t fit this combination: Propionibacterium or Corynebacterium are not typically branching and are not acid-fast; Listeria monocytogenes is non-branching; Haemophilus influenzae is Gram-negative. Thus the description points to Nocardia.

When you see a Gram-positive organism that forms branching filaments and stains only weakly acid-fast, with colonies described as dry, chalky, and crumbly—often called breadcrumb-like—you’re in the realm of Nocardia. These features come together because Nocardia is an aerobic actinomycete with cell walls rich in mycolic acids, which gives it partial acid-fastness (not as strong as Mycobacterium). The branching filaments reflect its filamentous, mold-like appearance, yet it is a bacterium, not a fungus. In culture, the colonies tend to look crumbly and bread-crumb-like, aiding its recognition.

Other Gram-positive rods don’t fit this combination: Propionibacterium or Corynebacterium are not typically branching and are not acid-fast; Listeria monocytogenes is non-branching; Haemophilus influenzae is Gram-negative. Thus the description points to Nocardia.

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