PRACTICAL IDENTIFICATION

OF COMMON

DERMATOPHYTES

KIMAIGA H.O

MBChB (University of Nairobi)

INTRODUCTION• Microscopic morphology of the micro and/or

macroconidia is the most reliable identification character

• Culture characteristics such as surface texture, topography and pigmentation are also a reliable criteria for identification.

• Clinical information such as the site, appearance of the lesion, geographic location, travel history, animal contacts and race is also important, especially in identifying rare non-sporulation species like M. audouini, T. concentricum and T schoenleinii etc.

Superficial species

• Trychophyton

• Microsporum

• Epidermophyton

Trichophyton spp

• Genus: characterized by development of both smooth-walled macro- and microconidia

• Macroconidia• Mostly borne laterally

• Directly on the hyphae or on short pedicele

• Thin or thick walled

• Clavate or fusiform

• Few or absent in many spp

• Smooth walled, mostly sessile (separate it from microsporum)

• Multiseptate macroconidia.

• Microconidia

• Spherical

• Fusiform to clavate

• NB: presence of

microconidia

distinguish this genus

from epidermophyton

Microconidium: Macroconidium:

T.mentagrophytes

• Macroscopic morphology• SDA colony texture

• Flat

• Some have central folding or develop raised central tufts

• Color• Front: white to cream, some

develop pleomorphic suede-like areas

• Reverse: yellow to brown to reddish brown

• Microscopic morphology• Lactophenol cotton blue

staining

• Spiral hyphae

• Macroconidia• Smooth., Thin-walled

• Clavate shaped, Multicelled

• Microconidia• Numerous (single celled), often

in clusters

• Hyaline, Smooth-walled

• Predominantly spherical to sub-spherical in shape

• Occasional clavate to pyriformforms may occur

• Also

• Spherical chlamydoconidia

T.soudanense

• Macroscopic

morphology

• SDA colony texture

• Flat to folded

• Suede-like surface

• Often there is a broad

fringe of submerged

growth

• Color

• Front and reverse both

deep apricot-orange

• Microscopic morphology• Lactophenol cotton blue

stain

• Hyphae: often show reflexive or right-angled branching

• Microconidia: pyriformmicroconidia may occasionally be present

• Chlamydoconidia: often found in older cultures (numerous)

T.tonsurans

• Macroscopic

morphology

• SDA colony texture

• May be considerable

variation

• Suede-like to powdery

• Flat with raised center

or folded, often with

radial grooves

• Colony color

• Front: may vary from

pale-buff to yellow to

reddish brown

• Reverse: varies from

yellow-brown -

reddish-brown - deep

mahogany

• Macroconidia

• Very occasional

• Smooth, thin-walled,

irregular, clavate

• May be present in some

cultures

• Older cultures present -

numerous swollen giant

microconidia and

chlamydoconidia

• Microscopic morphology

• Hyphae: relatively broad, irregular, much branched with numerous septa

• Microconidia:• Numerous

• Characteristic vary in size and shape:

• Long clavate to broad

• Pyriform: borne to right angles to the hyphae which often remain unstained

T.violaceum

• Macroscopic morphology• SDA colony texture

• Glabroue or waxy

• Heaped and folded

• SDA colony color• Deep violet

• Occasional non-pigment strains may occur

• Microscopic morphology• Lactophenol cotton blue

stain

• Hyphae

• Relatively broad, tortuous, much branched and distorted

• Young hyphae usually stain well

• Older hyphae stain poorly and show small central globules and granules

• No conidia usually seen

• *Occasional pyriformmicroconidia: observed on enriched media

• Numerous chlamydoconidia: usually present in older cultures

T.verrucosum• Macroscopic morphology

• SDA colony texture• Small, button or disk shaped

• Raised center

• Suede-like to velvety surface

• Flat periphery with some submerged growth

• Colony color• Front: whit to cream

• Reverse: pigment may vary from non-pigmented to yellow

• Microscopic morphology• Hyphae:

• Broad, irregular with many terminal intercalary chlamydospores - often in chains

• Tips of some are• Broad

• Club-shaped, occasionalydivided giving ʻantlerʼ effect

• Microconidia• Produced when itʼs grown on

thiamine-enriched media

• Occasional strains prod clavate to pyriformmicroconidia borne singly along the hyphae

• Macroconidia• Only rarely produced

• *Have a characteristic tail or string bean shape

Trichophyton scholeinii

Microsporum spp

• Form both macro- and

microconidia on short

conidiophores

• Macroconidia

• Hayline

• Multiseptate

• Variable in form

• Fusiform

• Spindle-shaped to

obovate

• Thin or thick ectinulate

to verrucose cell walls

• Microconidia• Hyaline

• Single-celled

• Pyriform to clavate

• *Not diagnostic for any one spp

• Basis of separation from the genus Trichophyton• Roughness of the

macroconidia cell wall

• May at times be difficult to observe

• NB: itʼs essential to observe macroconidiawhen identifying spp of mircosporum

Microsporum canis

• Macroscopic morphology

• SDA culture• Colony texture

• Wolly to cottony

• Flat to sparsely grooved

• Colony color• Front: white to yellowish

• Reverse: deep yellow to yellow-orange

• Microscopic morphology• Lactophenol cotton blue

staining

• Septate hyphae

• Macroconidia• Spindle shaped,

asymmetrical terminal apical knob

• 6-15 celled; long, rough & have thick outer cell walls.Rough cell wall (differentiates it from Trichophyton)

• Septal walls are thin

• Microconidia• Rare

• Unicellularly

• Clavate to pyriform in shape

Microsporum canis-

Lactophenol

Microsporum gypseum• Macroscopic

morphology

• SDA colonies• Powdery to granular

• Front: beige to cinnamon brown

• Reverse: yellow to brownish red

• Microscopic morphology• Lacto phenol blue

staining

• Produces:

• Septate hyphae

• Macroconidia:• Abundant fusiform

& symmetrical in shape with rounded ends

• Walls thin & rough

• 3-6 cells.

• Microconidia:• Moderately

numerous in number

• Club shaped

• Lateral along the hyphae

Don’t confuse with M. fulvum

Microsporu

m gypseum

Microsporum nanum

• Macroscopic

morphology

• SDA colony texture

• Powdery, Cottony

• Thin, Spreading

• Velvety or flat

• Often has some radial,

shallow furrows

• SDA colony color

• Front: White to dark beige

• Reverse: reddish-brown

• Microscopic

morphology

• Lactophenol cotton blue

staining

• Produces

• Septate hyphae

• Macroconidia

• 1-4 celled, Small, ovoid,

thin and echunate/rough

walls and broad truncate

bases

• Microconidia

• Club shaped

• Abundance may vary

Epidermophyton

• Clavate (club shaped) smooth walled conidia

and thick-walled chlamydoconidia

Epidermophyton flocossum