Trichophyton terrestre

Trichphyton terrestre (Fungus/Mould)

Ecology:

Trichphyton terrestre is a cosmopolitan (found everywhere), geophilic (soil loving) fungus.

It may also be recovered as a saprobe (living on dead organic matter) on the fur of small animals, presumably picked up from soils.

Pathology:

Trichophyton terrestre fails to grow once 35ºC to 37ºC is reached

As it fails to grow at human body temperature, there have been no reports of human infection by this fungus, nor has it been implicated in animal infections.

T.terrestre may occasionally be encountered as a laboratory contaminant.

Correct identification is important so as to not confuse it with pathogenic dermatophytes.

Macroscopic Morphology:

• Trichophyton terrestre exhibits moderate growth at 25ºC, maturing in about 8 days.

• Colonies expanded in diameter rather slowly.

• Colonies were off-white to light in colour.

• Reverse appeared yellowish to ochraceous, or even slightly reddish in colour.

• Texture was felty to powdery

The isolate presented here developed a pale to golden yellow exudate on prolonged incubation which was not reported in other sources.

 Trichophyton terrestre on SAB, 15 days incubation at 30˚C

Trichophyton terrestre on SAB,  25 days incubation at 30˚C

Microscopic Morphology:

• Trichphyton terrestre produces hyaline (clear, non-pigmented), septate hyphae.

• Microconidia (4 – 7 µm by 1 -5 µm) are tear-drop to slightly club-shaped.

• They are borne directly from the vegetative hyphae or are found on pedicles (stalk).

• Macroconidia (4 – 5 µm by 8 – 50 µm) have smooth, thin walls and usually contain between 2 to 6 cells or divisions internally.

• Macroconidia are cylindrical (parallel sides) or slightly clavate (club) shaped.

There may not be an obvious distinction between what may be called micro or macro conidia.  (ie. The two are not clearly differentiated.)

Free micro (& macro conidia) exhibit a truncate base or basal scar at what was their point of attachment.

Trichophyton terrestre - Adhesive tape preparation, 250X, LPCB (Nikon)

Trichophyton terrestre - Branching with development of Macro & Micro Conidia.

 LPCB 400X (DMD-108)

Trichophyton terrestre -as above

 LPCB 400X (DMD-108)

 Trichophyton terrestre - free macro & micro conidia

400+10X, LPCB (DMD-108)

Trichophyton terrestre - Conidia stain darker with the LPCB than the hyphae usually do

1000X, LPCB (DMD-108)

Trichophyton terrestre - Here again, the conidia at the tips of the hyphae (conidiophore) can be seen as staining a darker blue than the hyphae themselves.  Measurements shown (inset) are for the conidia and hyphe.  I regret that I didn't just measure the length of the conidia alone.

1000X, LPCB (DMD-108)

Trichophyton terrestre -extensive branching at near right angles.

1000X, LPCB (DMD-108)

Trichophyton terrestre -more of the same.  Darker blue conidia are seen at the end of the hyphae, branching at near right angles.

1000X, LPCB (DMD-108)

Trichophyton terrestre - divisions can be seen in some of the developing conidia (macroconidium)

1000X, LPCB (DMD-108)

Trichophyton terrestre -conidia staining a darker blue with the LPCB stain.  Divisions can be seen in the conidia.  The one on the lower left of the photo clearly has two.

1000X, LPCB (DMD-108)

Trichophyton terrestre -free macroconidium (4 septations or 5 compartments)

1000X, LPCB Nikon (appears larger due to cropping of photo)

Physiological Characteristics:

• Hair perforation test is POSITIVE

• Urease is POSITIVE

• BCPCG Media reaction is POSITIVE

• No growth at 35ºC to 37ºC

Trichophyton Agars:

Good growth on all Trichophyton agars.  No special growth requirements are required for growth.

Caution: on early growth, the fungus may somewhat resemble a Chrysosporium species.  Chrysosporium’s conidia generally do not exceed two cells in length.

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Trichophyton mentagrophytes Complex

Trichophyton mentagrophytes Complex (Fungus, Dermatophyte)

Ecology:  T.mentagrophytes is recognized as having two variants.  Anthropophilic isolates prefer man to animals while the zoophilic isolates primarily infect animals.  Small rodents appear to be the primary reservoir for the animal variety.  Trichophyton mentagrophytes is a cosmopolitan fungus (found everywhere).

Macroscopic Morphology:  T.mentagrophytes exhibits moderately rapid growth and matures within 6 – 10 days.  Sources have previously described anthropophilic isolates having a downy, powdery or even fluffy texture while zoophilic isolated were more granular in appearance.  Colonies may vary in colour from white to cream or yellowish.  The reverse also can vary from yellow to reddish brown to brown or ochre, depending on isolate and medium.

 Trichophyton mentagrophytes -5 days growth on SAB at 30^oC

 Trichophyton mentagrophytes - 14 days growth on SAB at 30^oC

Microscopic Morphology:  Trichophyton mentagrophytes produces septate hyphae from which branched conidiophores extend.  Sessile (not on stalk) microconidia are produced in rather dense, grape-like clusters on the conidiophores.  The microconidia (~2µm to 4µm) are spherical to pyriform in shape.  Macroconidia (20-50µm to 6-8µm) are cigar to club shaped and may show exhibit some distortion.  Macroconidia have a smooth exterior and are thin walled, usually have between 3 to 8 cells dividing the interior.  Macroconidia may be found more readily in younger cultures.  Production of both micro & macro conidia may vary with the isolate.  Coiled or spiral hyphae may be present and in some strains, structures described as nodular bodies or chlamydospores may be present.

Note: All photos which follow were taken with the DMD-108 digital microscope. 

T.mentagrophytes showing sessile microconidia along septate hyphae.

Note 100µm bar in upper right of this and several other photos. 

(400x, LPCB)

Trichophyton mentagrophytes - branched conidiophores bearing spherical conidia in clusters seen extending from septate hyphae.  (400x, LPCB)

T.mentagrophytes - another view as above.  A macroconidium can be seen near the lower center of the photo (400x, LPCB)

T.metagrophytes - a closer look at the branched condiophores bearing clusters of spherical microconidia.  Septations are visible in the hyphae and conidiophores.

(1000x, LPCB)

T.mentagrophytes -another look as in the previous photo.

(1000x, LPCB)

T.mentagrophytes - A 7-celled macroconidium.  Macroconidia are typically described as being cigar shaped or club shaped.

(400x, LPCB)

T.mentagrophytes - another 7-celled macroconidium with dimensions (inset)

(400+10x, LPCB)

T.mentagrophytes -an macroconidium which shows slight distortion (sides are not straight). Numerous spherical microconidia in lower right.

(1000x, LPCB)

T.mentagrophytes - a solitary cigar shaped macroconidium showing seven internal cells.  Walls are rather thin and the exterior is smooth.

(1000+10x, LPCB)

T.mentagrophytes - just by chance all this, and the previous macroconida all contain seven cells.  I found that young cultures (~3 days) produced the most macroconidia which seemed to diminish with additional incubation.  That said, the macroconidium pictured here is from a 6 day old slide culture.  It should always be kept in mind that structures may appear, disappear, develop or change with length of incubation.  It may be advisable to make several side cultures and harvest them at different time periods to observe development of structures.

(1000+10x, LPCB)

T.mentagrophytes - a couple of macroconidia are seen in this photo as well as clusters of microconidia.  A spiral hyphal element is seen in the upper center of the photo.

 (400+10x, LPCB)

T.mentagrophytes - a spiral hyphae is seen seen in the center left of this photo as it overlaps a macroconidium.  Microconidia throughout the photo.

(1000x, LPCB)

 T.mentagrophytes - more examples of spiral hyphae typical to T.mentagrophytes seen in this photo.

(400+10x, LPCB, 8 days incubation)

T.mentagrophytes - one last photo showing what is described as a nodular body or chlamydospore.  Clusters of microconidia seen in center-left.

(1000+10x, LPCB, 10 days incubation)

Physiological Tests:  a number of classical tests can be employed to speciate Trichophyton species.

·         Urease test: Positive

·         BCP-Milk Solids Glucose: Alkaline reaction

·         Hair perforation test: Positive

·         Growth at 37^oC: Excellent

·         Growth factor requirement*: None

*a variety of Trichophyton tubed agars are commercially available containing specific growth supplements (eg.inositol, thiamine, nicotinic acid, histidine).  The pattern or degree of growth in each can assist the speciation of Trichophyton.

Pathogenicity:  The anthropophilic strains are usually associated with chronic infections of glabrous skin, scalp, beard, nails and feet.

It is currently recommended* that Trichophyton mentagrophytes be reported as ‘Trichophyton mentagrophytes complex’ which also includes the former Trichophyton krajdenii.

*Best Practice by QMP-LS, external quality assessment agency.

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Trichophyton tonsurans

Trichophyton tonsurans (Fungus, Dermatophyte)

Pathogenicity and Distribution: Trichophyton tonsurans is a cosmopolitan (found worldwide) dermatophyte (a fungus of skin, nails or hair).  It is the etiologic agent most frequently implicated in ‘ringworm’ infections of the scalp (Tinea capitis) in America.  Causes an endothrix[i] infection of the hair (penetrates hair shaft to grow within).  T.tonsurans is anthropophilic (prefers humans to animals) however sources vary on its infectivity.  One prominent source[ii] suggests T.tonsurans is Zoophilic, but is frequently transmitted to man.  Others have speculated that equine strains may have mutated to become anthropophilic.  Infections are more commonly found in heavily populated urban regions

Macroscopic Morphology: T.tonserans may have highly variable colony morphology.  Surface growth may be white, beige, greyish or pale to sulphurous yellow, rose coloured to brownish.  The surface texture also can vary from velvety or powdery to suede-like, often with radial or concentric furrows.

 Trichopyton tonsurans: SAB agar at 30^o C after 14 days incubation, (Nikon)

Microscopic Morphology:  T.tonsurans produces septate hyphae.  The most prominent feature is the numerous microconidia formed along the hyphae or on short conidiophores which grow perpendicular to the originated hyphae.  The microconidia are sessile (attached by a ‘base’ rather than a ‘stalk’).  They can also be highly variable is shape ranging from pyriform (tear-drop) to clavate (club-like) to cylindrical and even larger round balloon-like forms.  Macroconidia are usually rare and also show variation in shape & size from cylindrical to cigar shaped (10 – 65 µm by 4 – 12 µm).  They are somewhat thick walled with a smooth surface and usually contain between 2 to 4 cells within each.  Terminal and intercalary chlamydospores may also be present, particularly in older cultures.  Another source[iii] has stated that spiral coils and arthroconidia may be present.

 Trichophyton tonsurans: Slide culture - First look at low power shows a mass of hyphae with microconidia visible on hyphae towards lower right of photograph.  (LPCB, DMD-108, X250)

 Trichophyton tonsurans: A closer look shows the microconidia growing along the hyphae.  This typical "birds on a wire" appearance is typical of Trichophyton species.  (LPCB, DMD-108, X400)

Trichophyton tonsurans:  Another look, as above. microconidia growing along hyphae.  Arrow shows a widening of the terminal end of a hyphal element, perhaps a young macroconidium or development of arthrospores?
  (LPCB, DMD-108, X400)

Trichophyton tonsurans: Microconida growing along the septate hyphae.

(LPCB, DMD-108, X1000)

 Trichophyton tonsurans: Another view showing the highly variable shape of the microconidia as well as an intercalary chlamydospore at the middle left of the photograph.

(LPCB, DMD-108, X1000)

Trichophyton tonsurans: Septate hyphae with microconida growing along its length.

(LPCB, DMD-108, X1000)

Trichophyton tonsurans:  Microconidia alongside septate hyphae with possible development of macroconidia at top left of photograph.  (LPCB, DMD-108, X1000)

Trichophyton tonsurans:  Again, microconidia along the length of a septate hyhal element.

(LPCB, DMD-108, X1000+10)

Trichophyton tonsurans:  Thickening of hyphal element - development of macroconida?  or arthrospores?  (LPCB, DMD-108, X1000)

Trichophyton tonsurans: two intercalary chlamydospores within the hyphae.

(LPCB, DMD-108, X1000+10)

Trichophyton tonsurans: Intercalary chlamydospore in an older culture.

(LPCB, DMD-108, Chlamydospore)

Trichophyton tonsurans:  Macroconidium - three visible divisions within.  T.tonsurans' macroconidia often show an irregular or wavy (undulating/ S-shaped) structure.

(LPCB, DMD-108, X1000+10)

Trichophyton tonsurans: Macroconidia in center of photograph.  Note micron bar at top of photo.

(LPCB, DMD-108, X1000)

Trichophyton tonsurans:  Stepping back a magnification, this photo shows the microconidia (MI) along the length of various hyphae, a possible macroconidium (MA) and what appears to be an intercalary chlamydiospore (CHL)  (LPCB, Nikon, X400)

Trichophyton tonsurans: (LPCB, DMD-108, X1000)

Trichophyton tonsurans:  Another photo just to get a better feel for the organism

(LPCB, DMD-108, X1000)

Trichophyton tonsurans:  Macroconidium -micron bar reads 20.23 µm.

(LPCB, DMD-108, X1000)

Physiological Tests:

·         Urease Positive

·         Hair perforation test –Negative (exceptions have been noted)

·         Usually causes alkalinisation of BCP-Milk solids-glucose media

·         Growth is stimulated by the addition of thiamine.

·         Growth at 37^oC

Definitive identification by molecular diagnosis is becoming more popular where available.

Differentiation:  The abundant microconidia of varying sizes and shapes assist in distinguishing this species from T.mentagrophytes and T.soudanense.  T.tonsurans response to thiamine also aids in this purpose.

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[i] Source states that hair perforation is variable – Guy St-Germain B.S., Richard Summerbell Ph.D. Star Publishing -further details to follow)

ⁱⁱ Atlas of Cinical Fungi, 2^nd edition: G.S. de Hoog, J. Guarro, J. Gené & M.J Figueras; Centraalbureau voor Shimmelcultures ‘ Universitat Rovira I Virgili, 2000: ISBN 90-70351-43-9

[iii] Medically Important Fungi – A Guide To Identification  5^th ed. Davise H. Larone, MT (ASCP), Ph.D., F(AAM),

ASM Press, Washington D.C.

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