Sarocladium kiliense

Sarocladium kiliense (Formerly Acremonium kiliense)

Note: Recent revision of the genus Acremonium has placed the mould formerly known as Acremonium kiliense into the genus of Sarocladium and therefore is now known as Sarocladium kiliense[i].  Sarocladium currently contains 16 species with Sarocladium oryzae as the ‘type’ species in the genus.

Ecology:

Sarocladium kiliense is a ubiquitous soil saprophyte commonly found in many environmental locations.

Pathology:

Immunocompetent hosts are rarely infected by Sarocladium kiliense.  Those with underlying immunological disorders may be predisposed to infection, whether local or progressively systematic.  Infection is usually through traumatic implantation of the mould leading to the development of a granuloma.  Endocarditis, CAPD-associated peritonitis and keratitis have been described in the literature.  Although rare, post-operative endopthalmitis has also been reported following cataract surgery[ii].   This emergent, opportunistic fungus may be resistant to common antifungal therapies[iii].

Sarocladium is known to contain a number of species pathogenic to plants.

Macroscopic Morphology:

The isolate presented here exhibited moderate growth, maturing in about 7 days on Sabouraud Dextrose agar at 30ᵒC.  Colony expansion was somewhat restricted.  The colony developed an off-white, greyish-white to light tan or pinkish colouration with fine, dry felt-like surface texture.  Delicate radial surface striations were evident.  Reverse appeared yellowish to light brown.

 Sarocladium kiliense -  10 days growth on Sabouraud-Dextrose Agar (SAB or SDA) at 30ᵒC (Nikon)

Microscopic Morphology:

Hyphae were hyaline, septate and narrow, often grouping together in cords (fascicled hyphae).  The delicate phialides appeared long (25 -45 µm), thin-walled and tapering.  The long phialides extending from the hyphae may have a basal septum, or if intercalary, they may produce a lateral phialidic (adelophialide) outgrowth of variable length, which lacks the basal septum.  Adelophialides may be found submerged in the medium.  Single-celled conidia are described as ellipsoidal to short cylindrical, (3 – 6 X 1.5 µm) in size.  Conidia accumulate in slimy masses around the tip of the conidiophore unless physically dispersed.  They, at times, may appear to “fall back” and accumulate along the sides of the conidiophore.  Cell arrangements are easily disrupted even when gentle care is taken with a slide culture.

Note:  The micron bar which appears in most photos may change scale between 100 µm to 50 µm without notice. When photographing at a magnification of 1000+10X, the bar extends past the borders of the screen at 100 µm.  It may or may not not be reset for subsequent photos at 1000X.

Sarocladium kiliense - long, thin and tapering phialides are appearant extending from the bundle of hyphae running diagonally through the photo.  (400X, LPCB, DMD-108)

 Sarocladium kiliense - again, the thin, delicate phialides extend from the parent hyphae with a bundle of conidia collected at the apex of each.  Single, free conidia also seen dispersed throughout the photo.  (400X, LPCB, DMD-108)

Sarocladium kiliense - and another photo.  Some phialides disappear out of the focal plane of the camera and only their bundle of conidia show where they re-emerge.

(400X, LPCB, DMD-108)

Sarocladium kiliense - perhaps a better shot of a row of phialides extending from the 'parent' hyphae with the conidia they have produced still clinging together at the apex. Many sources describe the accumulated conidia at the tip as being held together in "slimy" masses.  (400+10X, LPCB, DMD-108)

Sarocladium kiliense - a curious photo where the conidia seem to have 'fallen' down along side of the phailides which bore them.  Of course there is no gravity involved here, yet the tip of the phialide has no conidia which are found lined up along either side.
(400+10X, LPCB, DMD-108)

Sarocladium kiliense - often, these hyphae tend to form bundles or cords as they cling together.  Again, long thin, delicate phialides bear conidia at their tips.

(400+10X, LPCB, DMD-108)

Sarocladium kiliense - another view of the same.

(400+10X, LPCB, DMD-108)

Sarocladium kiliense - taken from the edge of a slide culture, this one phialide has a huge number of conidia accumulated around its tip.  Hard to say if this phialide is a 'hard working model employee', or just a 'hoarder', accumulating free conida drifting about that others had produced.  I quickly found out that the structures are very delicate and easily disrupted.

(400+10X, LPCB, DMD-108)

Sarocladium kiliense - at a higher magnification.

(1000X, LPCB, DMD-108)

Sarocladium kiliense - as above.  I'll add some more until you 'get the picture' or 'get bored'!

(1000X, LPCB, DMD-108)

Sarocladium kiliense - a bundle of hyphae running diagonally through the photo.  The delicate phialides are about 25 -45 µm in length, thin-walled and tapering.

(1000X, LPCB, DMD-108)

Sarocladium kiliense -   Single-celled conidia are described as ellipsoidal to short cylindrical, (3 – 6 X 1.5 µm) in size.  I'm not sure as to what structure my arrow points to at the base of the phialide as it doesn't really look like a conidium nor a chlamydospore.

(1000+10X, LPCB, DMD-108)

Sarocladium kiliense - nicely stacked conidia and hyphae arranged in 'cords' (fascicled hyphae).
(1000X, LPCB, DMD-108) 

 

 Sarocladium kiliense - phialides extending from the hyphae may have a basal septum (arrow).

(1000+10X, LPCB, DMD-108)

Sarocladium kiliense - as seen above, the long phialides extending from the hyphae may have a basal septum, or if intercalary, they may produce a lateral phialidic outgrowth
(adelophialide) of variable length which lacks a basal septum.
(1000+10X, LPCB, DMD-108)

Sarocladium kiliense - the shape of the conidia differs from the pointy-ended, curved shape of Fusarium species which also may be produced at the ends of phialides, similar to that shown here.
(1000+10X, LPCB, DMD-108)

Sarocladium kiliense - rather than a short phialide, this one (center-left) can probably be traced back under the bundle of hyphae.  (1000+10X, LPCB, DMD-108)

Sarocladium kiliense - stepping back a bit in magnification, the massive numbers of conidia produced is well demonstrated in this photograph.  (400X, LPCB, DMD-108)

Sarocladium kiliense - a first look at the fungus when it arrived in the lab in transport, it appeared as above.  (400X, LPCB, DMD-108)

Sarocladium kiliense - round structures were repeatably viewed amongst the mass of hyphae.
(1000X, LPCB, DMD-108)

Sarocladium kiliense - these ones measured at 2.8 µm  and  3.2 µm in diameter however the sources I consulted stated the mature chlamydospores of Sarocladium kiliense are 4 - 8 µm in diameter .
(1000X, LPCB, DMD-108)

Sarocladium kiliense - I cannot find any reference to the dimensions of the chlaymydospores that Sarocladium kiliense produces.  If not an artifact, I can only suspect that these structures are the chlamydospores sources mention in relation to this organism.
(1000+10X, LPCB, DMD-108)

Sarocladium kiliense - another photo as above.
(1000+10X, LPCB, DMD-108)

Sarocladium kiliense -intercalary chlamydospore (insert)

(1000X, LPCB, DMD-108)

Most Acremonium species are phenotypically similar and therefore other means, such as molecular techniques, are required to accurately speciate isolates.  Often it is sufficient to report the isolate simply as Acremonium species.  It was through molecular means that it was determined that the fungus previously referred to as Acremonium kiliense differed sufficiently to be reclassified as a Sarocladium.

One feature which is unique to this former Acremonium is that it frequently produces terminal and/or intercalary chlamydospores.  Therefore, if you have isolated a mould which looks in every other way like an Acremonium species, yet chlamydospores are present – you probably have a Sarocladium kiliense.

Physiology:

The isolate presented here grew well at ambient room temperature and at 30ᵒC.  It showed reduced growth at 35ᵒC and failed to grow at 37ᵒC, therefore would probably not be pathogenic for humans.

This isolate was urea positive.

 

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[i] Acremonium phylogenetic overview and revision of Gliomastix, Sarocladium, and Trichothecium

Summerbell RC, Gueidan C, Schroers HJ, de Hoog GS, Starink M, Rosete YA, Guarro J, Scott JA. 2011.

Stud Mycol 68:139-162, 2011

[ii] Acremonium kiliense Endopthalmitis That Occurred after Cataract Extraction in an Ambulatory Surgical Center and was traced to an Environmental Reservoir.

Scott K. Fridkin, Frederic B. Kremer, Lee A. Bland, Arvind Padhye, Michael M. McNeil and William R Jarvis.

Clin Infect Dis: 22 (February), pg. 222 – 227, 1996

[iii] In Vitro Evaluation of Antifungal Drug Combinations against Sarocladium (Acremonium) kiliense, an

Opportunistic Emergent Fungus Resistant to Antifungal Therapies.

Fabiola Fernández-Silva, Javier Capilla, Emilio Mayayo, Deanna Sutton, Josep Guarro

Antimicrob. Agents Chemother. February 2014 vol. 58 no. 2 1259-1260

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