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Which factor contributes to the limitation of fungal culture applications?
Which factor contributes to the limitation of fungal culture applications?
What temperature range do most molds grow best at?
What temperature range do most molds grow best at?
Which of the following fungi is considered hazardous according to laboratory safety considerations?
Which of the following fungi is considered hazardous according to laboratory safety considerations?
What is the typical incubation period for detecting the presence of yeast in the mouth, throat, or vagina?
What is the typical incubation period for detecting the presence of yeast in the mouth, throat, or vagina?
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Which of the following fungi grows best at temperatures of 25 to 27 °C?
Which of the following fungi grows best at temperatures of 25 to 27 °C?
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What is the correct incubation period for respiratory specimens suspected to contain dimorphic fungus?
What is the correct incubation period for respiratory specimens suspected to contain dimorphic fungus?
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What medium should all specimens be inoculated onto for fungal culture?
What medium should all specimens be inoculated onto for fungal culture?
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How often should culture plates be checked during the first week of incubation?
How often should culture plates be checked during the first week of incubation?
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At what temperature and duration should Candida be grown for the Germ Tube Test?
At what temperature and duration should Candida be grown for the Germ Tube Test?
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Which of the following statements is true regarding the Urease Test for C.albicans?
Which of the following statements is true regarding the Urease Test for C.albicans?
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What is the main purpose of the Germ Tube Test?
What is the main purpose of the Germ Tube Test?
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What characteristic feature distinguishes isolates of Trichophyton mentagrophytes in the Hair Perforation Test?
What characteristic feature distinguishes isolates of Trichophyton mentagrophytes in the Hair Perforation Test?
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Which organism is associated with a positive result in the Rapid Urease test on Christensen’s Urea Agar?
Which organism is associated with a positive result in the Rapid Urease test on Christensen’s Urea Agar?
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What are the two methods of reproduction mentioned for fungi?
What are the two methods of reproduction mentioned for fungi?
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Which of the following accurately describes the tease mount technique?
Which of the following accurately describes the tease mount technique?
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What is the main disadvantage of the cellophane tape method?
What is the main disadvantage of the cellophane tape method?
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What distinguishes slide culture as a method for observing fungi?
What distinguishes slide culture as a method for observing fungi?
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Which of the following spore arrangements are mentioned in the content?
Which of the following spore arrangements are mentioned in the content?
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Which species of Candida is characterized by light green colored smooth colonies?
Which species of Candida is characterized by light green colored smooth colonies?
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Which type of fungus is known for its rapid growth, taking only 24 hours to culture?
Which type of fungus is known for its rapid growth, taking only 24 hours to culture?
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Which of the following is a common carbon source used in media for fungal growth?
Which of the following is a common carbon source used in media for fungal growth?
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What color are the colonies of C.tropicalis usually described as?
What color are the colonies of C.tropicalis usually described as?
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Which feature is NOT typically used to describe the colonial morphology of fungi?
Which feature is NOT typically used to describe the colonial morphology of fungi?
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If a fungal colony appears to be cream to white and smooth, which species is it likely to be?
If a fungal colony appears to be cream to white and smooth, which species is it likely to be?
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What is the texture of a colony that is described as velvety?
What is the texture of a colony that is described as velvety?
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Trichosporon and Trichophyton spp. are detected using which type of medium?
Trichosporon and Trichophyton spp. are detected using which type of medium?
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Which medium is primarily used for the isolation of fungi directly from specimens?
Which medium is primarily used for the isolation of fungi directly from specimens?
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Which component is added to culture media to prevent bacterial growth?
Which component is added to culture media to prevent bacterial growth?
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What is the primary use of Potato Dextrose Agar?
What is the primary use of Potato Dextrose Agar?
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What is the function of Cycloheximide when added to culture media?
What is the function of Cycloheximide when added to culture media?
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Which medium is recommended for the cultivation of fastidious pathogenic fungi?
Which medium is recommended for the cultivation of fastidious pathogenic fungi?
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What is the unique characteristic of CHROMagar Candida Medium?
What is the unique characteristic of CHROMagar Candida Medium?
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Dermatophyte Test Medium (DTM) is used for which kind of specimens?
Dermatophyte Test Medium (DTM) is used for which kind of specimens?
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Which agar is known for its ability to induce pigment production in Cryptococcus neoformans?
Which agar is known for its ability to induce pigment production in Cryptococcus neoformans?
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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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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.
