Neoscytalidium dimidiatum (formerly Scytalidium dimidiatum)
-Arthric synamorph of Nattrassia mangiferae
-Species, until recently known under the picnidial synamorph name of Hendersonula toruloidea occurs on a wide variety of tropical fruit trees, sometimes causing branch rot.
Macroscopic; Rapid growth quickly filling the plate, mature within three days. Effuse, hairy or wooly colonies which are white to greyish (or dark grey to blackish brown) with a cream colour to an ochraceous-yellow reverse. Melanin deficient mutants may occur.
Growth inhibited by cycloheximide therefore will not grow on selective media such as that used for dermatophyte isolation.
Microscopic; Branched and septate hyphae with no conidiophores. Arthroconidia (3-6 X 5-15 µm) develop and are 1-2 cells in length, flattened on the ends and may be rectangular, square, as well as oval to roundish becoming barrel shaped. The wide hyphae (6 -10 µm), and arthroconidia are brown (melanin) while the narrower side branches of the hyphae tend to produce pale arthroconidia. Melanin free variants (previously known as Scytadidium hyalinum) do occur, producing hyphae and arthroconidia that are invariably colourless but are identical to Neoscytalidium dimidiatum in every other way.
A picnidial form very occasionally develops in very old cultures and is currently considered to be Fusicoccum dimidiatum (formerly thought to be Nattrassia mangiferae. Picnidia, when present are large (100 - 300 µm). Picnidial conidia are hyaline when young with age but as they age may develop 1- 5 septa with a dark brown central region. Picnidia may be induced by prolonged growth on sterilized lemon or banana skins.
Pathogenicity; Known to cause nail and skin infections with rare reports of deep-seated infections such as brain infections, sinusitis, lymphadenitis and endophthalmitis with higher incidence of fungemia in immunocompromised patients. Infection is primarily found in patients from tropical to sub-tropical regions.
Neoscytalidium dimidiatum on SAB agar after 3 days incubation.(click on photo to enlarge for better viewing)
Neoscytalidium dimidiatum on SAB agar Reverse & Surface after 5 days growth.Surface shows impression where hyphae were removed in celluloid tape examination.
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Hyphae 40X LPCB
Broad Septate Branching Hyphae (6 -10 µm)Note narrower, un-pigmented side branches.
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Dark (melanin), Broad, Septate, Branching Hyphae (6 -10 µm)Arthroconidia present. (X400)
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Broad septate hyphae and contiguous arthroconidia (LPCB X 400)(click on photo to enlarge for better viewing)
Ditto(click on photo to enlarge for better viewing)
Pigmented arthroconidia as contiguous cells.(click on photo to enlarge for better viewing)
Arthroconidia (LPCB X600)(click on photo to enlarge for better viewing)
Broad septate hyphae and two celled conidia.Unstained preparation from Corn Meal Agar (magnification not noted)
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