Mycology Flashcards
Name a dematiaceous organism that causes dermatophytosis?
Epidermophyton floccosum, Trichophyton spp.
Which fungal organism, categorized as a dermatophyte, is the most common cause of athletes foot.
Trichophyton rubrum
Explain the hair perforation test and compare and contrast endothrix and exothrix hair infections
Prepubital hair is cut into 1cm pieces and placed in 25ml of sterile water and incubated for up to four weeks. After incubation the hair is interpreted with lactophenol cotton blue. If the fungal organism has the ability to penetrate the hair shaft it is considered an endothrix infection whereas an exothrix infection is only seen on the surface of the hair shaft. Trichophyton mentagrophytes is positive and Trichophyton rubric is negative.
How is the urease test performed on fungal cultures and which Trichophyton species is typically negative for this test?
The urease test is performed exactly the same as when it is performed for bacteria cultures. Trichophyton rubric is the only species that is urease negative.
Discuss the characteristics of a fungal organism.
Fungal organisms are all considered heterotrophs and obtain all of their nutrients by absorption through their surrounding environments. Their cells walls are made up of mostly the carbohydrate chitin. All are eukaryotic cells.
Explain how rice grain agar is utilized and what organisms are differentiated by its use.
Rice used to differentiate between Microsporum canis and Micosporum audouinii. Micosporum audouinii grows poorly or not at all where the organism was inoculated and will turn brown. Whereas Microsporum canis will show good growth and the rice will turn yellow from the pigment produced by the organism.
Compare and contrast dematiaceous and hyaline.
Organisms that are considered hyaline do not produce a pigment and are without color these organisms appear blue because of lactophenol cotton blue stain used. Macroscopically these organisms typically have a light colony. Organisms that are dematiaceous have the ability to produce the pigment melanin, which is a dark brown to black pigment, and colonies appear dark green to black.
List the pathogenicity of the fungal organisms that are considered superficial. Hortaea wernekii Malassezia furufur Piedraia hortae Trichosporon spp
Hortaea werneckii - tinea nigra. Hyphomycete, two-celled yeast-like cells
Malassezia furfur - pityriasis vericolor folliculitis, catheter-associated sepsis, dandruff. Bowling pin or bottle pop key feature
Piedraia hortae - black peidra. highly septate dematiaceous hyphae, swollen intercalary cells
Trichosporon spp. - White peidra-disseminated disease in immunocompromised patients with neutropenia
Define the descriptors used for colony morphology of fungus and fungus like bacteria.
Cottony
Velvety
Granular/powdery
Glabrous
Flat
Rugose
Umbonate
Verrucose
Cottony - high aerial hyphae or loose and course texture
Velvety - low aerial hyphae
Granular/powdery - looks like grains of sand or powdered sugar
Glabrous - very smooth or waxy
Flat - having no topography
Rugose - hilly, veins radiate out from center
Umbonate - circular depression or elevation in the center
Verrucose - wrinkled, veins go in any direction throughout colony
Identify the structures found in the cell wall of fungal organisms.
- Mannoproteins
- Beta-(1,6)-glucan
- Beta-(1,3)-glucan
- Chitin
- Phospholipid bilayer of cell membrane (of interlinked Ergosterol)
List the diseases associated with subcutaneous mycosis and the common characteristics seen on the tissue biopsy. Identify the leading cause of chromoblastomycosis, phaeohyphomycosis, mycetomas, and sporotrichosis.
Chromoblastomycosis - Sclerotic bodies are seen in the tissue and the leading cause is Fonsecaea pedrosoi
Phaeohyphomycosis - Mycelium are seen in the tissue and the leading cause is Cladophialophoria bantianai
Mycetoma - Granules are seen in the tissue and the leading cause of white grain mycetoma is Acremonium
Sporotrichosis is not noted with a characteristic structure seen in tissue the leading cause of sporotrichosis is Sporothrix schenckii
List other terms used to describe chromoblastomycosis.
Verrous dermatitidies, Sclerotic bodies, Cauliflower lesion
Describe the mode of action of intraconazole and how the antifungal agent is administered.
The mode of actions is 14-alpha demethylase and it can be administered orally or intravenously, belongs to the Triazole group.
Compare and contrast the stain methods used to identify fungal organisms.
Lactophenol cotton blue is used as both a mounting fluid and a stain. The lactic acid acts as a clearing agent and a preservative for the organism, the phenol is a killing agent, and the cotton blue (aniline blue). Most fungal organisms appear dark blue when using the gram stain method.
Acid-Fast stain is used to differentiate eumycotic organisms. India ink is used for the identification of the capsule produced by Cryptococcus neoformans. Calcoflour white is a fluorescent stain the is absorbed by the chitin found in the cell wall of the fungal organism.
Compare and contrast the eumycotic mycetoma and actinomycotic mycetoma.
Actinomycotic mycetoma are caused by bacterial organisms where as eumycotic mycetoma are caused by fungal organisms. The organisms most frequently associated with actinomycotic mycetoma are Actinomadura, Nocardia, and Streptomyces. Organisms most often associated with eumycotic infections are Pseudallescheria boydii, Rhinocladiella, Madurella, .
Define aspergillosis and identify the organisms responsible for causing the disease and what is the most effective treatment used.
Aspergillosis is a very rare fungal disease. ABPA is most often seen in patients with asthma or cystic fibrosis Charcot-Leyden crystals may be present. Invasive aspergillosis damages body tissue in patients who are immunocompromised “fungus balls” are often seen in these infections. The most effective treatment for aspergillosis is Voriconazole.
Describe the clinical significance and microscopic characteristics of Aspergillus flavus.
Causes Aspergillus ear and Kernel rot.
Conidial heads in shades of yellow-green to brown and dark sclerotia
List the general characteristics of the zygomycetes and the patient populations most often infected with organisms found in this group.
Extremely fast growing, woolly, and gray to brown. Large ribbon like hypae that contain occasional septa. Affect diabetes patients and patients on prolonged antibiotics
Compare and contrast the tease mount method and the cellophane tape method for microscopic examination
Tease mount - remove a small portion of growth and place the growth in the drop Lactophenol Blue on the slide. Gently tease the fungus apart so that it is thinly spread out in the Lactophenol.
Cellophane tape method - Cut a piece of clear tape and press the adhesive side of the tape onto the surface of the colony and pull it away.
Explain the media used in fungal cultures.
Sabourauds
Sabourauds - Type of agar growth medium containing peptones. It is used to cultivate dermatophytes.
Discuss the caffic acid test and the significance of positive results.
Detect the ability of an organism to produce the enzyme phenyloxidase, which is useful for the identification of Cryptococcus neoformans
Describe the term dimorphic
Exist in the form of both mold and yeast. This is usually brought about by change in temperature.
Discuss the five dimorphic organisms or systemic fungal agents that are most often pathogenic to humans. Included in your discussion should be what the organisms look like both macroscopically and microscopically at both 25°C(room temp) and 37 °C(body temp).
Blastomyces dermatitidis
Blastomyces is found in a filamentous mold form at 25C. At 37C it grows in a discrete yeast form.
This organism is the etiologic agent of blastomycosis.
Discuss the five dimorphic organisms or systemic fungal agents that are most often pathogenic to humans. Included in your discussion should be what the organisms look like both macroscopically and microscopically at both 25°C(room temp) and 37 °C(body temp).
Coccidioides species
25C - Hyphae and arthroconidia are produced. Hyphae are hyaline, septate and thin. Racquet hyphae may occasionally be observed.
37C - Large, round, thick-walled spherules filled with endospores are observed.
Causes coccidioidomycosis
