Mold of the month: Sarocladium kiliense ((Grütz) Summerbell 2011)
Sarocladium kiliense from pure culture. Incubated for seven days at 25 °C on DG18 agar. In direct comparison to colonies on MEA, it is quickly noticed that the osmotic stress of DG18 plates leads to a significant change in colony morphology. The mold colonies of Sarocladium kiliense not only grow significantly slower on DG18, but overall "pathological" and poor. Hardly any synnemata and few spores are formed at this stage. The colonies remain colorless to slightly white and, particularly in the case of competitive pressure from other molds, the impression of a yeast colony may arise on cursory observation.
Sarocladium kiliense from pure culture. Incubated for seven days at 25 °C on MEA agar. The circular colony forms only weak color pigments and remains generally white to very slightly yellowish. The entire colony grows very flat on the culture medium surface and forms synnemata (bundled mycelial strands) which stand out from the medium and at the tip of which the spores are formed in small heads. Sarocladium kiliense is comparatively weak in competition with other molds, so that the colony size shown is achieved almost exclusively by pure cultures but never in the presence of other molds (data not shown).
Sarocladium kiliense - indoor moisture indicator and classified in biological risk group 2.
The mold species Sarocladium kiliense was first described in 1926 under the name Cephalosporium kiliense. Since then, no less than 18 further taxonomic descriptions of this mold species have followed under a wide variety of species and genus names. On closer inspection, it is striking that Sarocladium kiliense was by no means only obtained from natural habitats such as soil samples or plant litter, but also appears in a large number of medical journals. Even in the most recent version of the Altas of Clinical Fungi (4th Ed. 2020), Sarocladium kiliense is described as an accompanying organism in a whole range of clinical pictures. The most common are skin diseases and lung infections. This also results in the classification of Sarocladium kiliense in biological risk group 2 (see TRBA 460:2016).
In the indoor sector, Sarocladium kiliense is of interest not only because of its classification in biological risk group 2, but also because of its high water requirement, due to which this mold generally occurs on moist to wet materials (Food and Indoor Fungi Sec. Ed.). Sarocladium kiliense, like the species Sarocladium strictum, is one of the recognized indoor moisture indicators whose elevated detection may indicate moisture damage. In older literature, both species are still listed under the generic name Acremonium. Since both Sarocladium kiliense and Sarocladium strictum have a high water requirement and can also only be reliably distinguished morphologically after prolonged incubation, the two species are often combined under the generic name Acremonium or Sarocladium in routine analysis (Food and Indoor Fungi Sec. Ed.).
Sarocladium kiliense not only grows extremely filigree and whitish under laboratory conditions. On wallpaper and other building materials, even a large-scale infestation is often not visible to the naked eye, which is why laboratory samples with specific preparation and staining techniques are relevant for detection. Adhesive film preparations or material samples are particularly suitable for this purpose. The genus Sarocladium (= Acremonium) can also be detected in indoor air samples, but experience has shown that it is much rarer.
Light microscope image of spore carriers
Light microscope image of spore carriers of the mold species Sarocladium kiliense. The species forms very fine and elongated phialides (spore carriers), at the end of which usually less than 10 small elliptical - lanceolate spores are formed. As a characteristic of the whole genus Sarocladium, the spores are formed into small "heads" (round aggregation at the end of a phialid) so-called "slimy heads". The individual spores are only loosely attached to the end of the heads, which is why they often disintegrate during preparation. The preparation is stained with cotton blue.
Light microscope image of mycelial aggregates, spores and chlamydospores (large round to egg-shaped permanent spores)
One of the most important differential features to other representatives of the genus Sarocladium are the so-called chlamydospores, which are formed in older colonies (approx. 2 weeks) under laboratory conditions. The clamydospores develop directly in the mycelium and are strangulated with increasing age. Since clamydospores are formed very close to the substrate, they can only be removed from the colonies by means of squeeze preparations. The preparation is stained with cotton blue and taken from an OA plate (oatmeal agar).