Dermatophytes are a group of fungi that can infect the keratinized tissues of skin, hair, and nails of both humans and animals. They include genera such as Microsporum, Trichophyton, and Epidermophyton. Dermatophytes produce enzymes that allow them to utilize keratin as a nutrient source. Laboratory diagnosis involves microscopic examination of samples as well as culturing to isolate the fungus. Isolates are then identified based on characteristics such as macroconidia morphology and colonial growth. Direct examination and culturing allow diagnosis of infections like ringworm and tinea.

2. DEFINITION:
Closely related group of fungi that have
great affinity to invade the keratinized
part of the skin, hair, nail, wool, horn
hoof and feathers.
They cause ringworm in animals and
tinea in humans.

3. • Dermatophytes have the ability to utilize
keratin as a nutrient source, i.e. they have a
unique enzymatic capacity [keratinase].
• Other enzymes also secreted by dermato-
phytes:elastases and proteinases,which
cosidered as virulence factors.

4. • The disease process in dermatophytosis (ring
worm) is unique for two reasons: Firstly, no
living tissue is invaded the keratinized
stratum corneum is simply colonized.
However, the presence of the fungus and its
metabolic products usually induces an
allergic and inflammatory eczematous
response in the host.

5. • Secondly, the dermatophytes are
the only fungi that have evolved a
dependency on human or animal
infection for the survival and
dissemination of their species.

6. • Most dermayophytes belong to the Fungi
imperfecti and are classified in three
anamorphic genera:
1. Microsporum
2. Trichophyton
3. Epidermophyton
• A few species have been placed in the teleo-
morphic genus Arthroderma in phylum
Ascomycota

7. • Dermatophytes are strict aerobes ,most of
which grow slowly on standard SDA.
• Can resist cyclohexamide in the medium.
• A few require special growth factors, which
are supplied by the addition of yeast extract
to the SDA.
• T.equinum needs nicotinic acid, and
T.verrucosum needs thiamine and inositol for
growth.

8. • Macroconidia and miroconidia are produced
in culture.
• The cultures of many dermatophytes are
pigmented.
• Colonial morphology and the type of macro-
conidia produced are used for identification.
• Arthrospores are the infectious forms ,most
often associated with tissue invasion by this
group of fungi.

9. • These resistant forms can remain viable for
more than 12 months in suitable
environment in buildings.
• They are released by fragmentation of
hyphae in keratinized structures.
• Dermatophytosis affects many animal
species.The disease is a zoonosis and most
human infection caused by Microsporum
canis contracted from infected cats.
• Contagious.

10. • Dermatophytes can be grouped on
the basis of their habitats and the
host preferences as:
• Geophilic
• Zoophilic
• Anthropophilic
USUAL HABITAT

11. Geophilic dermatophytes
• Inhabit and replicate in association with
decomposing keratinous materials such as
hairs or feathers.
• Animals can acquire infection with geophilic
dermatophytes from soil or from contact
with infected animals.
• Some species may cause infections in man
following contact with soil, for example:
• Microsporum gypseum .

12. Zoophilic dermatophytes
• Zoophilic species are primarily parasitic on
animals and infections may be transmitted to
humans following contact with the animal host.
• Zoophilic infections usually elicit a strong host
response and on the skin where contact with
the infective animal has occurred i.e
arms, legs, body or face,for example:
1. Microsporum canis
2. Trichophyton equinum
3. Trichophyton verrucosum

13. Anthropophilic dermatophytes
• The common anthropophilic species are
primarily parasitic on man .They are unable
to colonize other animals and they have no
other environmental sources.
• For example:
• Epidermophyton fluccosum
• Trichophyton rubrum
• Trichophyton mentagrophytes

14. Ringworm in animals

15. Ringworm in animals

16. Ringworm in animals

17. Ringworm in animals

20. Ringworm in animals

21. Tinea in humans

22. Tinea in humans

23. Tinea in humans

24. Tinea in humans

25. Direct microscopy of infected
materials
• Skin Scrapings, nail scrapings
and epilated hairs should be
examined using 10% KOH or
calcofluor white mounts.

26. KOH mount of infected skin scales

27. KOH mount of infected nails

28. Hair invasion
• Hairs treated with KOH should be examined
microscopically for the presence of arthro-
spores.
• The arrangement of arthrospores on hair is
called ectothrix,which either:
1-Large ectothrix.
2-Small ectothrix.
.

29. Hair invasion
1-Large ectothrix,5-8 microns in sparse chains
inside and outside of hair such as:
M.gypseum,M.nanum,T.equinum
2-Large ectothrix in chains,which include:
a-Megaspores type(5-10 microns)
e.g T.verrucosum
b-Microides type(3-5microns)
e.g T.mentagrophytes
c-Intermediate types
e.g T.rubrum,T.megninii

30. Hair invasion
• When the arthrospores arranged inside the
infected hair, it is typically endothrix,such as:
• T. violaceum ,T.sodanense.
• Favic type: special type of endothrix hair
invasion in which hyphae are not break up
into arthrospores but die and left air
spaces.e.g.T. schoenleinii

31. Hair invasion

32. Hair invasion

33. Hair invasion

34. Hair invasion

35. Hair invasion

36. Laboratory diagnosis of
dermatophytes
A-Sampling:
1-Lesions should be cleaned by soap & water or
disinfected with alcohole 70% using a piece of gauze.
2-A specimen of scales,nail or hair should be free
from extraneous material such
dirt,sebum,ointments,antifungal agents,………it
should first be removed with an alcowipe.
3-. Using a blunt scalpel, tweezers, or a bone
curette, firmly scrape the lesion, particularly at the
advancing border(peripheries of the lesions), hair
stumps are epilated by forceps.

37. Laboratory diagnosis of dermatophytes

38. Laboratory diagnosis of
dermatophytes
• 5-Suitable material from cats can also be
collected on a large sheet of paper by
bruching the caot with a clean toothbrush
• 6-Skin and nail specimens may be scraped
directly onto special black cards, which make
it easier to see how much material has been
collected and provide ideal conditions for
transportation to the laboratory.

39. Laboratory diagnosis of
dermatophytes

40. Laboratory diagnosis of
dermatophytes
B-Ultraviolet (Wood’s light) examination :
• Hair infected with parasitic Mirosporum spp
may be detected by the yellow green
fluorescence in ultraviolet light.
• The Wood’s light is useful to detect M.canis
infection in cats,dogs and other small
animals.

42. Laboratory diagnosis of
dermatophytes
• In tinea capitis caused by parasitic Microsporum
species(M.canis,M.distortum,M.audouinii&
M.ferrugineum) the parasitized hairs are usually
but not always fluorescent yellow green.
• T. schoenleinii gives dull green fluorescence.
• Fluorescence is dependent on the host animal
as well as on the dermatophyte species.
• The Fluorescence of hair with dermatophyte
infections appears to be due to treptophan
metabolites.

44. Laboratory diagnosis of
dermatophytes
• D-Isolation of dermatophytes(culturing):
1-Specimens should be inoculated onto primary
isolation media, like Sabouraud's dextrose agar
containing cycloheximide (actidione) and
chloramphenicol,incubated at 26-28C for up to 4
weeks.Isolation of T.verrucosum(cattle ringworm)is
favored at 37C. The growth of any dermatophyte is
significant.
2-Multiple cultures are recommended whenever a
cotamination proplem can be anticipated,i.e it is
better to culture each sample onto more than one
tube.

45. Laboratory diagnosis of
dermatophytes
• Addition of DMSO permits quick examination
often whithout warming.
• Adition of DMSO or glycerine prevents rapid
drying of the fluid,permits observation of the
slide for up to 24 or 48 hours.
• Slides may be ringed with finger nail polish to
save for longer peroids.

46. Laboratory diagnosis of
dermatophytes
3-Especial growth requirments can be determined
Using commercially-available tricophyton agar:
T1=control medium(casein basal medium).
Other media,produced by adding growth factors to the
basal agar such as:
T3=containing thiamine & inositol for isolation of
T.verrucosum.
T4=containing thiamine only for isolation of
T.verrucosum.
T5=containing nicotinic acid for isolation of T.equinum.

47. Laboratory diagnosis of
dermatophytes
4-Dermatophyte test medium(DTM)has been
formulated to differentiate dermatophytes from
contaminating fungi.
• Phenol red is used as a pH indicator in this
medium.
• Growth of dermatophytes results in alkaline
metabolic products and the color of the medium
changes from yellow to red.
• Other fungal media should be used in
conjunction with DTM because some
contaminating fungi can induce a color change.

48. Laboratory diagnosis of dermatophytes
• In addition,the color change in DTM can obscure
the characteristic pigmentation required for
differentiation of dermatophyte species.
A.Dermatophyte Test Medium (DTM)
Sterile medium yellow.
B. DTM Positive
DTM plate on the right showing color
change after two day's growth;
Microsporum canis

49. Laboratory diagnosis of
dermatophytes
• Identification criteria for isolates:
• Colonial morphology,texture,pigmentation
and growth rate.
• Microscopic appearance of macroconidia
and other structures such as
microconidia,spirals,chlamydospores…………

50. Macroconidia of dermatophytes
• Trichophyton
• Microsporum
• Epidermophyton

51. EPIDERMOPHYTONMICROSPORUMTRICOPHYTON
•Club shape.
•Thin to moderately
thick wall
• Fusiform or
spindle shape,
• Thick wall,
• Rough surface
Cylindrical or pencil
shape,
Smooth thin wall,
Rarely present
Macroconidia
1-91-151-12Number of
septa
Usually absentUsually sessile or
stalked and
arranged singly
along the hyphae.
• More abundant,
• May be globose,
pyriform or clavate.
• Are borne singly or in
group- like clusters
Miroconidia

52. Laboratory diagnosis of
dermatophytes
• There are three forms of colonies:
• a-Membranous form: the aerial mycelium is entirely
absent and the vegetative mycelium is in compact
masses e.g.T.verrucosum,T.violaceum…..
• b-Filamentous form: the aerial mycelium is more or
less high and dense
e.g.M.canis,M.rubrum,E.floccosum.
• c-Granular-powdery form:characterized by extensive
conidia and absence of aerial filaments e.g.
T.mentagrophytes,T.equinum.

53. Laboratory diagnosis of
dermatophytes
The isolated cultures are
examined by the following
technique:
1-Wet mount technique.
2-Slide culture technique
(microculture technique).
3-Cellophane tape preparation.

54. 1-Wet mount preparation

55. 2-Slide culture technique
It’s a protocol for transferring fungal
colonies to a microscope slide.

56. 2-Slide culture technique

57. 2-Slide culture technique

58. 3-Cellophane tape preparation
• The protocol involves using cellophane tape
and a wooden applicator stick.
• The tape is attached to the applicator stick as
a handle and then the tape is touched to the
fungal colony and finally, stuck to a slide with
a drop of LPCB stain.
• The cellophane tape remains as part of the
mounting.

59. 3-Cellophane tape preparation

60. Microsporum canis

61. T. mentagrophytes

62. T.mentagrophytes

63. T.verrucosum

64. T.verrucosum