A dematiaceous mold grew in 4 days on Sabouraud agar, isolated from a foot wound. The organism is most likely identified by chaining macroconidia with longitudinal and horizontal septations. Which genus does this description most support?

A dematiaceous mold grew in 4 days on Sabouraud agar, isolated from a foot wound. The organism is most likely identified by chaining macroconidia with longitudinal and horizontal septations. Which genus does this description most support?

• A. Curvularia
• B. Scopulariopsis
• C. Alternaria
• D. Paecilomyces

Answer: (C)

Chaining multicellular conidia with both longitudinal and transverse septations is a hallmark of Alternaria, a dematiaceous mold. The macroconidia are dark-pigmented, long and multicellular, and they appear in long chains with septa running in two directions, giving a muriform (cross‑wall) appearance. This distinctive conidial morphology—muriform, chained macroconidia in a pigmented mold from a foot wound—points most strongly to Alternaria. Other dematiaceous genera have different conidial features. Curvularia tends to have curved conidia with a swollen central cell and doesn’t exhibit the same muriform chain pattern. Scopulariopsis produces conidia in chains that are often rough-walled and barrel-shaped but lacking the characteristic muriform crosswalls. Paecilomyces forms elongated conidia in chains along phialides but also lacks the muriform, two-direction septation pattern seen with Alternaria.

Chaining multicellular conidia with both longitudinal and transverse septations is a hallmark of Alternaria, a dematiaceous mold. The macroconidia are dark-pigmented, long and multicellular, and they appear in long chains with septa running in two directions, giving a muriform (cross‑wall) appearance. This distinctive conidial morphology—muriform, chained macroconidia in a pigmented mold from a foot wound—points most strongly to Alternaria.

Other dematiaceous genera have different conidial features. Curvularia tends to have curved conidia with a swollen central cell and doesn’t exhibit the same muriform chain pattern. Scopulariopsis produces conidia in chains that are often rough-walled and barrel-shaped but lacking the characteristic muriform crosswalls. Paecilomyces forms elongated conidia in chains along phialides but also lacks the muriform, two-direction septation pattern seen with Alternaria.