Reading Assignment (Mycology)

Hair, skin, or nails

For dermatophyte culture, which types of specimens are generally contaminated with bacteria, rapidly growing fungi, or both?

Not acceptable

In mycology, collection of specimens through swabbing are:

False positive

Pus should be collected through aspiration since the use of cotton buds may give ____________________ microscopic results.

Wood lamp

It helps identify infected hairs by causing them to fluoresce

Skin and nails

Which specimen/s should be cleaned with 70% isopropyl alcohol before sampling?

Nail specimen

It may be submitted as scrapings or cuttings

Sterile scissor

It is used to cut complete nails into small thin strips

Isolator tube

It is a method for the recovery of molds and dimorphic fungi

• It has a high contamination rate

Heparinized bone marrow

Which type of specimen should be plated directly onto media at the bedside?

Blood culture bottles

Not recommended for blood & bone marrow specimens

Cerebrospinal fluid (CSF)

Which specimen should be concentrated by centrifugation before inoculation?

Grinding

It is recommended for KOH and calcofluor white preparations if there is enough tissue

Abscess fluid, wound exudates, and tissue

Which specimens should be gently minced?

Nebulizer

It is used to induce sputum

Non-viscous specimens

For which types of specimens should you inoculate directly onto media with a sterile pipette?

Oropharyngeal candidiasis

In respiratory specimens, it is typically diagnosed with direct smear and culture

Cycloheximide

Which antimicrobial agent should be avoided when plating nasal sinus specimens?

Urine, feces, and vaginal secretions

These specimens are commonly submitted for bacteriologic culture, but occasionally may grow yeast that needs identification

24-hour urine specimen

What type of urine specimen is not acceptable for processing?

TRUE

TRUE OR FALSE

Direct examination of clinical specimens could be stained or unstained

10%

What is the KOH concentration for skin & hair?

20%

What is the KOH concentration for hard tissues?

FALSE

TRUE OR FALSE

Specimens collected from sterile sites needs KOH

To increase the rate of clearing

In using KOH, what is the purpose of heating?

Calcofluor white

It binds to polysaccharides present in chitin of the fungus or to cellulose

India ink

It can be used to examine CSF for the presence of encapsulated yeast Cryptococcus

Periodic-Acid-Schiff (PAS)

• It attaches to polysaccharides in the fungal wall and stains fungi pink

• To demonstrate details of fungal elements

• Detects fungi in tissues

Grocott methenamine silver stain (GMS)

Demonstrates melanin; best permanent mount

Giemsa stain

Used primarily to detect Histoplasma in blood or bone marrow?

Fontana-Masson stain

Stains melanin in the cell wall and identifies the presence of phaeoid fungi.

RT / 30°C

Most laboratories routinely incubate fungal cultures at?

35 °C

If the causative agent suspected is a dimorphic fungus, cultures should also be incubated at?

Mucorales

They grow rapidly and may fill the tube or petri dish w/ aerial mycelium within a few days

Color, texture, and growth rate

Which gross morphologic traits are observed in fungal cultures?

Direct mounting of the fungal isolate

The most common procedure for microscopic examination is:

Lactophenol cotton blue (LPCB)

It is used to fix and stain tease or tape mounts from cultures

Frosted tape

Fungi are not visible using which type of cellophane tape?

Cellophane tape preparation

An advantage of this procedure is that the conidial arrangement is retained

Slide culture

It is useful for demonstrating the natural morphology of fungal structures and for encouraging conidiation in some poorly fruiting fungi.

T. rubrum

In the hair perforation test, it causes only surface erosion of hair shafts

T. mentagrophytes

In the hair perforation test, it typically forms perpendicular penetration or wedge-shaped pegs in the hair shafts

Hair perforation test

This test may be used to distinguish penetration-capable M. canis from M. equinum, which does not penetrate hair

M. audouinii

It does not grow but turns the rice grains brown

Germ tube production

This test is a relatively easy test to perform for the identification of yeasts

C. albicans and C. dubliniensis

Which fungi is/are identified with germ tube production?

Carbohydrate assimilation test

This test can be readily performed as part of routine identification protocols

Cornmeal agar

Yeast morphology on what type of agar is useful in determining identification of yeasts?

Blastoconidia

The characteristic budding yeast forms usually seen on direct mounts of yeasts

Chlamydoconidium

It is a thick-walled conidium formed within or at the end of vegetative hyphae

Pseudohyphae

These are produced when the blastoconidia germinate to form a filamentous mat

Arthroconidia

It begins as true hyphae but break apart at the cross-walls with maturity.

Blue

What is the color of a positive KNO3 assimilation result?

Yellow

What is the color of a negative KNO3 assimilation result?

Cryptococcus spp.

They have weak growth at 35°C and no growth at 42° C

25°C

What is the optimal growth temperature for Cryptococcus spp.?

Christensen urea agar

Yeast isolates producing the enzyme urease can be detected easily with?

(1,3)-B-D-Glucan

An important component of the cell wall of various fungi, including pathogenic yeasts and molds

Galactomannan

A component of the Aspergillus cell wall, within plasma or BAL fluid

Fluconazole

It is the leading agent for treating yeast infections but has limited to no activity against molds