Practical identification of common dermatophytes
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Transcript of Practical identification of common dermatophytes
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