FUNGAL CULTURE & IDENTIFICATION
When do I do it?
- In every patient with suspected fungal infection
What can I find?
- White, woolly colonies with a yellowish reverse pigment
- Thick walled, spindle-shaped macroconidia with knobs at the ends and typically more than six internal compartments
- Granular, beige cultures with yellowish reverse pigment
- Abundant thin-walled macroconidia with six or fewer internal compartments
- White powdery-looking colonies with
- Very few, cigar-shaped macroconidia and large numbers of small round microconidia
What do I need?
- Dermatophyte test medium (DTM), clear sticky tape, slides, microscope, methylene blue or DiffQuick® blue
How do I do it?
- Use a scalpel with water to scrape and hemostats to pluck; take hairs and scale from the edge of a lesion (preferably the ones fluorescing under the Wood's light)
- Impress hairs and scale gently on DTM; do not screw the lid tight
- Incubate the agar at 20-25°C (a warm space with moisture is better)
- Check the agar daily over a 3 week period
- Color change (pH change) that occurs when the colony is still small and then spreads as the colony grows is indicative of dermatophytes
- When the colony is 10-14 days old, impress clear sticky tape (sticky side down) gently on the suspicious colonies and lay it down onto a drop of methylene blue or other stain on a slide.
- Evaluate the sample under a microscope with the condenser up. The sticky tape acts as its own cover slip.
Tip
- If the patient has no clearly circumscribed lesion or an asymptomatic carrier is suspected use the McKenzie toothbrush technique.
- Brush the hair with a new toothbrush for about 5 minutes
- Gently place the hairs and scale, using a sterile needle, onto the agar or cut the bristles with sterile scissors
- Put all the material (bristles, hairs, scale) onto the agar
- Agar color changes can also occur with saprophyte colonies, particularly as they age. Daily examination of the culture is imperative to notice a color change that accompanies a growing culture.
abscess
A discrete swelling containing purulent material, typically in the subcutis
alopecia
Absence of hair from areas where it is normally present; may be due to folliculitis, abnormal follicle cycling, or self-trauma
alopecia (“moth-eaten”)
well-circumscribed, circular, patchy to coalescing alopecia, often associated with folliculitis
angioedema
Regional subcutaneous edema
annular
Ring-like arrangement of lesions
atrophy
Thinning of the skin or other tissues
bulla
Fluid-filled elevation of epidermis, >1cm
hemorrhagic bullae
Blood-filled elevation of epidermis, >1cm
comedo
dilated hair follicle filled with keratin, sebum
crust
Dried exudate and keratinous debris on skin surface
cyst
Nodule that is epithelial-lined and contains fluid or solid material.
depigmentation
Extensive loss of pigment
ecchymoses
Patches due to hemorrhage >1cm
epidermal collarettes
Circular scale or crust with erythema, associated with folliculitis or ruptured pustules or vesicles
erosion
Defect in epidermis that does not penetrate basement membrane. Histopathology may be needed to differentiate from ulcer.
erythema
Red appearance of skin due to inflammation, capillary congestion
eschar
Thick crust often related to necrosis, trauma, or thermal/chemical burn
excoriation
Erosions and/or ulcerations due to self-trauma
fissure
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
fistula
Ulcer on skin surface that originates from and is contiguous with tracts extending into deeper, typically subcutaneous tissues
follicular casts
Accumulation of scale adherent to hair shaft
hyperkeratosis
Excessive stratum corneum, confirmed via histopathology. This term is often used to describe the nasal planum and footpads.
hyperpigmentation
Increased melanin in skin, often secondary to inflammation
hypopigmentation
Partial pigment loss
hypotrichosis
Lack of hair due to genetic factors or defects in embryogenesis.
leukoderma
Lack of cutaneous pigment
leukotrichia
Loss of hair pigment
lichenification
Thickening of the epidermis, often due to chronic inflammation resulting in exaggerated texture
macule
Flat lesion associated with color change <1cm
melanosis
Increased melanin in skin, may be secondary to inflammation.
miliary
Multifocal, papular, crusting dermatitis; a descriptive term, not a diagnosis
morbiliform
A erythematous, macular, papular rash; the erythematous macules are typically 2-10 mm in diameter with coalescence to form larger lesions in some areas
nodule
A solid elevation >1cm
onychodystrophy
Abnormal nail morphology due to nail bed infection, inflammation, or trauma; may include: Onychogryphosis, Onychomadesis, Onychorrhexis, Onychoschizia
onychogryphosis
Abnormal claw curvature; secondary to nail bed inflammation or trauma
onychomadesis
Claw sloughing due to nail bed inflammation or trauma
onychorrhexis
Claw fragmentation due to nail bed inflammation or trauma
onychoschizia
Claw splitting due to nail bed inflammation or trauma
papule
Solid elevation in skin ≤1cm
papules
Solid elevation in skin ≤1cm
paronychia
Inflammation of the nail fold
patch
Flat lesion associated with color change >1cm
petechiae
Small erythematous or violaceous lesions due to dermal bleeding
phlebectasia
Venous dilation; most commonly associated with hypercortisolism
plaques
Flat-topped elevation >1cm formed of coalescing papules or dermal infiltration
pustule
Raised epidermal infiltration of pus
reticulated
Net-like arrangement of lesions
scale
Accumulation of loose fragments of stratum corneum
scar
Fibrous tissue replacing damaged cutaneous and/or subcutaneous tissues
serpiginous
Undulating, serpentine (snake-like) arrangement of lesions
telangiectasia
Permanent enlargement of vessels resulting in a red or violet lesion (rare)
ulcer
A defect in epidermis that penetrates the basement membrane. Histopathology may be needed to differentiate from an erosion.
urticaria
Wheals (steep-walled, circumscribed elevation in the skin due to edema ) due to hypersensitivity reaction
vesicle
Fluid-filled elevation of epidermis, <1cm
wheal
Steep-walled, circumscribed elevation in the skin due to edema