Fungal Culture Methods and Safety
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Questions and Answers

Which factor contributes to the limitation of fungal culture applications?

  • No requirement for specific media
  • The pathogen's rapid growth rate
  • Cultivability in most infected individuals
  • Reliable axenic culture not yet achieved for some pathogens (correct)

What temperature range do most molds grow best at?

  • 35 – 40 °C
  • 30 – 35 °C
  • 25 – 30 °C (correct)
  • 15 – 20 °C

Which of the following fungi is considered hazardous according to laboratory safety considerations?

  • Aspergillus
  • Coccidioides immitis (correct)
  • Candida
  • Histoplasma capsulatum

What is the typical incubation period for detecting the presence of yeast in the mouth, throat, or vagina?

<p>7 days (A)</p> Signup and view all the answers

Which of the following fungi grows best at temperatures of 25 to 27 °C?

<p>Sporothrix schenckii (A)</p> Signup and view all the answers

What is the correct incubation period for respiratory specimens suspected to contain dimorphic fungus?

<p>28 days (B)</p> Signup and view all the answers

What medium should all specimens be inoculated onto for fungal culture?

<p>General purpose fungal medium (D)</p> Signup and view all the answers

How often should culture plates be checked during the first week of incubation?

<p>Twice (B)</p> Signup and view all the answers

At what temperature and duration should Candida be grown for the Germ Tube Test?

<p>37°C for 3 hours (A)</p> Signup and view all the answers

Which of the following statements is true regarding the Urease Test for C.albicans?

<p>C.albicans is urease negative. (A)</p> Signup and view all the answers

What is the main purpose of the Germ Tube Test?

<p>To differentiate Candida albicans from other yeasts (A)</p> Signup and view all the answers

What characteristic feature distinguishes isolates of Trichophyton mentagrophytes in the Hair Perforation Test?

<p>They form extensive localized areas of pitting and erosion. (C)</p> Signup and view all the answers

Which organism is associated with a positive result in the Rapid Urease test on Christensen’s Urea Agar?

<p>Cryptococcus (B)</p> Signup and view all the answers

What are the two methods of reproduction mentioned for fungi?

<p>Sexual and asexual (B)</p> Signup and view all the answers

Which of the following accurately describes the tease mount technique?

<p>It requires the organism to be grown on plated medium. (C)</p> Signup and view all the answers

What is the main disadvantage of the cellophane tape method?

<p>The organism must be grown on plated medium. (C)</p> Signup and view all the answers

What distinguishes slide culture as a method for observing fungi?

<p>It is the best method for preserving and observing actual fungal structures. (B)</p> Signup and view all the answers

Which of the following spore arrangements are mentioned in the content?

<p>Sporangiospores, blastospores, conidia, ascospores (B)</p> Signup and view all the answers

Which species of Candida is characterized by light green colored smooth colonies?

<p>C.albicans (A)</p> Signup and view all the answers

Which type of fungus is known for its rapid growth, taking only 24 hours to culture?

<p>Zygomycetes (A)</p> Signup and view all the answers

Which of the following is a common carbon source used in media for fungal growth?

<p>Glucose (dextrose) (A)</p> Signup and view all the answers

What color are the colonies of C.tropicalis usually described as?

<p>Blue to metallic blue (A)</p> Signup and view all the answers

Which feature is NOT typically used to describe the colonial morphology of fungi?

<p>Olfactory response (C)</p> Signup and view all the answers

If a fungal colony appears to be cream to white and smooth, which species is it likely to be?

<p>C.glabrata (C)</p> Signup and view all the answers

What is the texture of a colony that is described as velvety?

<p>Silky (A)</p> Signup and view all the answers

Trichosporon and Trichophyton spp. are detected using which type of medium?

<p>Urea Agar (D)</p> Signup and view all the answers

Which medium is primarily used for the isolation of fungi directly from specimens?

<p>Sabouraud Dextrose Agar (D)</p> Signup and view all the answers

Which component is added to culture media to prevent bacterial growth?

<p>Chloramphenicol (C)</p> Signup and view all the answers

What is the primary use of Potato Dextrose Agar?

<p>Inducing clinical fungi to produce conidia (D)</p> Signup and view all the answers

What is the function of Cycloheximide when added to culture media?

<p>It reduces the growth of certain fungi. (B)</p> Signup and view all the answers

Which medium is recommended for the cultivation of fastidious pathogenic fungi?

<p>Brain Heart Infusion Agar (C)</p> Signup and view all the answers

What is the unique characteristic of CHROMagar Candida Medium?

<p>It allows definitive differentiation of common yeast species. (C)</p> Signup and view all the answers

Dermatophyte Test Medium (DTM) is used for which kind of specimens?

<p>Specimens from hair, skin, or nails (C)</p> Signup and view all the answers

Which agar is known for its ability to induce pigment production in Cryptococcus neoformans?

<p>Birdseed Agar (A)</p> Signup and view all the answers

Flashcards

Fungal Culture Method

Technique for growing fungi in a lab setting; involves inoculation onto a general-purpose fungal medium.

Culture Media for Fungi

Specialized growth mediums specifically designed for fungi, allowing them to thrive and for quick isolation.

Incubation period for Fungi

Time required for fungal growth in a lab setting; typically ranges from 1-4 weeks

Optimal Growth Temperature (Molds)

25-30°C (77-86° F)

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Optimal Growth Temperature (Yeasts)

35-37°C (95-98°F)

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Safety Considerations

All mold cultures and clinical specimens must be handled in a Class II biologic safety cabinet

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Limitations of Fungal Culture

Some fungal species difficult to grow in lab; others grow too slowly

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Incubation Time for Specimens

14 days for general samples, shorter for direct tests (7 days), longer for certain samples(21-28 days).

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Sabouraud Dextrose Agar (SDA)

A common medium for isolating fungi from samples.

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Malt Extract Agar

A good medium for identifying, isolating, and counting yeasts and molds.

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Potato Dextrose Agar

A common medium for clinical fungi that shows pigment and conidia production. Ideal for slide cultures.

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Chloramphenicol

An additive to culture media that inhibits bacterial growth.

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Cycloheximide

An additive to culture media that reduces the growth of environmental fungi.

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Brain Heart Infusion (BHI) Agar

A recommended medium for fastidious pathogenic fungi, like Histoplasma capsulatum and Blastomyces dermatitidis.

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Dermatophyte Test Medium (DTM)

Used to grow dermatophytes, fungi that affect hair, skin, and nails.

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SABHI Agar

A combination of Sabouraud Dextrose Agar (SDA) and Brain Heart Infusion (BHI) Agar.

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Growth Rate of Dimorphic Fungi

Dimorphic fungi, like Histoplasma capsulatum, Blastomyces dermatitidis, and Paracoccidioides brasiliensis, grow slowly, taking 1-4 weeks to become visible.

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Growth Rate of Zygomycetes

Zygomycetes are rapid growers, becoming visible within 24 hours.

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Growth Rate of Dematiaceous Fungi

Dematiaceous fungi, also known as "black yeasts" and environmental molds, typically take 1-5 days to develop.

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Colony Shape

Fungal colonies can have various shapes, like circular, filamentous, or irregular.

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Colony Size

The size of a fungal colony is important for identification. Tiny colonies are called "punctiform."

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Colony Elevation

This describes the side view of a colony, how it rises above the agar surface.

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Colony Margin

The edge of a fungal colony can be smooth, wavy, or irregular.

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Colony Surface Topography

The texture of a fungal colony can be flat, rugose (wrinkled), folded, crateriform (like a crater), verrucose (wart-like), or cerebriform (brain-like).

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What are the types of fungal spores?

Spores are reproductive units produced by fungi. Key types include conidia, blastospores, sporangiospores, and ascospores.

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What is a tease mount?

A quick method for examining fungal cultures under a microscope. Involves disrupting the colony and observing spores directly on a slide.

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Cellophane Tape Mount

A method to prepare fungal cultures for microscopic examination using cellophane tape to capture aerial hyphae.

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Slide Culture

The gold standard for observing the detailed structure of fungi. Involves growing the fungus on a slide to preserve its natural form.

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When is a tease mount done?

A tease mount is often conducted prior to a slide culture as a preliminary step to identify potential Histoplasma, Blastomyces, or Coccidioides species.

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Germ Tube Test

A simple test to distinguish Candida albicans from other yeasts by observing its ability to form a germ tube in serum at 37°C within 3 hours.

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Rapid Urease Test

A test used to identify certain fungi based on their ability to produce the enzyme urease. A positive result indicates the presence of Cryptococcus, Rhodotorulla, Trichosporon, or Trichophyton mentagrophytes.

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Ferric Citrate Test

A test specifically designed to identify Cryptococcus neoformans, a fungus that causes cryptococcal meningitis.

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Hair Perforation Test

A test used to differentiate Trichophyton isolates. T. mentagrophytes creates distinct pits and erosion patterns on hair, while T. rubrum does not.

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What does a positive Hair Perforation Test result indicate?

A positive result indicates the presence of Trichophyton mentagrophytes, a fungus that creates a distinctive pattern of pitting and erosion on hair.

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Study Notes

Fungal Culture Method

  • All specimens should be cultured on a general-purpose fungal medium.
  • Fungal cultures can be used to isolate specific pathogens.
  • Some fungi take a long time to grow (1-4 weeks).
  • Safety precautions: Handle cultures and specimens in a Class II biologic safety cabinet.

Laboratory Safety

  • Dimorphic fungi (especially C. immitis) are hazardous.
  • All mold cultures and clinical specimens must be handled in a Class II biologic safety cabinet.
  • No exemptions.

Reasons for Culture Limitations

  • Reliable axenic cultures (isolating one organism free from others) of Pneumocystis jirovecii are not always feasible.
  • Some pathogens are only cultivable in minority of patients, eg, Candida or Aspergillus.
  • Certain pathogens (e.g., Histoplasma capsulatum) grow too slowly for timely diagnosis.

Temperature Requirements

  • Most molds grow best at 25–30°C.
  • Most yeasts grow best at 35–37°C.
  • Sporothrix schenckii grows best at 25-27°C, not 30°C.

Incubation Period

  • General incubation period: 14 days.
  • Specifics: 7 days for vaginal, throat, or mouth specimens to detect yeast; 21 days for tissues and non-blood sterile specimens; 28 days for respiratory, bone marrow, and blood specimens (in cases with suspected dimorphic fungi).
  • Plates should be checked twice weekly during the first week (looking for rapidly growing isolates), and weekly thereafter.

Importance of Culture Media Selection

  • General purpose: Sabouraud dextrose, malt extract, and sometimes brain heart infusion medium.
  • Chloramphenicol: Added to prevent bacterial growth (reduces Actinomyces yield).
  • Cycloheximide: Added to reduce environmental fungi (reduces Aspergillus, Candida neoformans, and Mucorales yield).

Media Uses

  • Sabouraud dextrose agar (SDA): Primary isolation medium for fungi directly from specimens.
  • Malt extract agar: Good for detecting, isolating, and enumerating yeast and molds.
  • Potato dextrose agar: Clinically encountered fungi; used to induce pigment and conidia production for slide cultures.
  • Corn meal agar with Tween 80: Distinguishing yeast genera and species, especially Candida, and to stimulate conidiation.
  • Birdseed agar (Niger seed, Staib agar): Differentiating C. dubliniensis from Candida albicans.
  • Brain heart infusion (BHI) agar: Cultivating fastidious pathogenic fungi, including Histoplasma capsulatum and Blastomyces dermatitidis.
  • Dermatophyte test medium (DTM): Specimens from hair, skin, or nails incubated at room temperature; dermatophytes change the medium color (from yellow to red) within 14 days using phenol red.
  • CHROMagar Candida Medium: Useful for isolating yeasts, like those from throats, urine, genitals, or blood cultures to confirm yeast presence. Includes differentiation of C. albicans, C. tropicalis, C. glabrata, and C. krusei.
  • Urea Agar:
  • Rice Agar: Detecting Trichosporon, Trichophyton species, Microsporum audouinii and M. canis.

General Considerations for Mold Identification

  • Growth rate varies vastly (e.g., dimorphic fungi grow slower = 1-4 weeks, rapid growers = 24hrs, dematiaceous fungi= 1-5 days)
  • Growth requirements (Vary by species, but often need sources of carbon, nitrogen, vitamins.) The most common are glucose (dextrose), then fructose, and mannose, and sometimes sucrose).
  • Colonial morphology (features for identification): form (shape), size, elevation, margin, texture, opacity, and color.

Microscopic Examination Methods

  • Tease Mount: Disturbing colonies from their slide position for rapid conidia and spore identification.
  • Cellophane Tape Mount (Cellotape Flag method): Pressing tape to the colony surface and transferring to a slide for viewing fungal structures. Preserves characteristics of fungal structures.
  • Slide Culture: Allows in-depth microscopic observation of fungal morphology, useful for identifying Histoplasma, Blastomyces, Coccidioides and Cladophialophora bantiana.

Special Tests

  • Germ Tube Test: Differentiating Candida albicans from other yeasts.
  • Rapid Urease test (Christensen's Urea Agar): distinguishing Cryptococcus, Rhodotorulla, Trichosporon species, Trichophyton mentagrophytes.
  • Ferric Citrate Test (for C. neoformans):
  • Hair perforation test: distinguishes Trichophyton mentagrophytes from T. rubrum, based on different localized area pitting/erosion.

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Mycology: Fungal Culture Methods PDF

Description

This quiz covers essential protocols in fungal culture methods, focusing on safety precautions and temperature requirements for optimal growth. It elaborates on the limitations and special considerations for culturing specific fungal pathogens. Test your knowledge on the handling of fungal specimens in laboratory settings.

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