Mycology: Fungi Characteristics, Structure & Growth
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Questions and Answers

How do thermally dimorphic fungi adapt to different temperature environments?

  • They exist as yeasts in the environment and molds in human tissues.
  • They exist as molds both in the environment and in human tissues, regardless of temperature.
  • They exist as yeasts both in the environment and in human tissues, regardless of temperature.
  • They exist as molds in the environment at ambient temperature and as yeasts (or other structures) in human tissues at body temperature. (correct)

What is the primary nutritional mode of fungi, and why are they often found associated with decaying matter?

  • Chemotrophic; they derive energy from inorganic chemical reactions.
  • Heterotrophic; they rely on preformed organic sources of carbon, obtaining nutrients from decaying matter. (correct)
  • Phototrophic; they convert light energy into chemical energy.
  • Autotrophic; they produce their own organic compounds using photosynthesis.

Which characteristic distinguishes 'Fungi imperfecti' from other fungi?

  • Their capacity to cause disease in plants but not in animals.
  • Their exclusive reliance on asexual reproduction. (correct)
  • Their preference for living in extreme environments.
  • Their ability to perform photosynthesis.

A researcher is examining a fungal sample and observes structures formed externally on a pedestal. Which type of sexual spore is the researcher most likely observing?

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

Why are the shape, color, and arrangement of conidia important in mycology?

<p>They provide crucial characteristics for identifying different species of fungi. (A)</p> Signup and view all the answers

Coccidioides immitis utilizes which type of asexual spore for transmission?

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

Which of the following characteristics is NOT typical of fungi?

<p>Presence of vascular tissue (D)</p> Signup and view all the answers

How does Candida albicans differ from most other fungi in terms of its natural habitat?

<p>It is a part of the normal human flora. (A)</p> Signup and view all the answers

Which of the following statements accurately describes the role of granulomas in response to fungal infections?

<p>Granulomas are a characteristic response in major systemic fungal diseases like coccidioidomycosis, histoplasmosis, and blastomycosis. (B)</p> Signup and view all the answers

A patient has a negative skin test for a specific fungal antigen. Which interpretation is MOST accurate, assuming the patient is not immunocompromised?

<p>The patient has likely never been exposed to the fungus. (D)</p> Signup and view all the answers

How does normal skin flora contribute to host defense against fungal infections?

<p>By inhibiting the growth of fungi such as <em>Candida albicans</em> through competition and other mechanisms. (B)</p> Signup and view all the answers

Which of the following is NOT a recognized mechanism of host defense against fungal infections in the respiratory tract?

<p>The release of endotoxins by fungi to stimulate a localized inflammatory response. (B)</p> Signup and view all the answers

A patient is taking broad-spectrum antibiotics for a bacterial infection. Which of the following fungal-related complications is MOST likely to arise as a consequence?

<p>Overgrowth of <em>Candida albicans</em> leading to a yeast infection. (B)</p> Signup and view all the answers

What does a positive skin test to a fungal antigen indicate?

<p>Exposure to the fungal antigen at some point in the past. (A)</p> Signup and view all the answers

Why is cell-mediated immunity crucial in defending against fungal infections?

<p>It is involved in granuloma formation to contain the fungi. (D)</p> Signup and view all the answers

How do fatty acids on the skin contribute to the defense against dermatophytes?

<p>By inhibiting the growth of dermatophytes. (D)</p> Signup and view all the answers

In Loop-mediated Isothermal Amplification (LAMP), what is the primary role of the FIP and BIP primers?

<p>To initiate loop-mediated autocycling amplification by recognizing the strands synthesized by F3 and B3 primers. (C)</p> Signup and view all the answers

Why are tests for the presence of antibodies more useful in diagnosing Systemic Mycoses compared to other fungal infections?

<p>Systemic Mycoses often induce a significant and detectable antibody response in serum or spinal fluid. (B)</p> Signup and view all the answers

What is the main reason drugs effective against bacterial diseases are ineffective against fungal diseases?

<p>Fungi possess specific structures absent in bacteria, such as ergosterol. (C)</p> Signup and view all the answers

How do azole drugs work in combating fungal infections?

<p>They inhibit the synthesis of ergosterol, an essential component of fungal membranes. (B)</p> Signup and view all the answers

What is the significance of observing a significant rise in antibody titer when diagnosing fungal infections?

<p>It confirms the diagnosis of the fungal infection, similar to bacterial and viral serologic testing. (C)</p> Signup and view all the answers

Why is Amphotericin B an effective antifungal drug?

<p>It disrupts fungal cell membranes at the site of ergosterol. (C)</p> Signup and view all the answers

How does Caspofungin function as an antifungal medication?

<p>By inhibiting the synthesis of β-glucan, a component of fungal cell walls. (B)</p> Signup and view all the answers

In the context of diagnosing Cryptococcal Meningitis, what is the purpose of the Latex Agglutination Test?

<p>To detect the presence of polysaccharide capsular antigens of <em>C.neoformans</em> in CSF. (B)</p> Signup and view all the answers

Which of the following mycoses affects the deeper tissues and organs of the body?

<p>Deep or Systemic Mycosis (B)</p> Signup and view all the answers

A patient presents with symptoms of liver damage after consuming a wild mushroom. Which toxin is most likely responsible for these effects?

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

Ergotism, a mycotoxicosis, results from the ingestion of alkaloids produced by which mold?

<p><em>Claviceps purpurea</em> (B)</p> Signup and view all the answers

Aflatoxins are metabolized by the liver into what compound, which is a potent carcinogen?

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

Which of the following is the primary mechanism by which Aflatoxin B1 contributes to the development of hepatic carcinoma?

<p>Mutation in the p53 tumor suppressor gene (C)</p> Signup and view all the answers

What type of hypersensitivity reaction is typically associated with allergies to fungal spores, such as those of Aspergillus?

<p>Immediate Type I Hypersensitivity (D)</p> Signup and view all the answers

Which clinical finding is least likely to be associated with an allergy to fungal spores?

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

A patient presents with liver damage and a history of consuming spoiled grains and peanuts. Which of the following fungal toxins is the most likely cause?

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

In fluorescence in situ hybridization (FISH), what is the primary purpose of using rRNA-targeted probes, as exemplified by the MY1574 domain-specific probe?

<p>To identify and visualize specific microbial taxa within a mixed population. (C)</p> Signup and view all the answers

What is the function of the positive controls used in DNA macroarray hybridization?

<p>To confirm the efficacy of the hybridization and detection process. (A)</p> Signup and view all the answers

In multiplex tandem PCR, what is the key advantage of simultaneously targeting multiple pathogens, such as Candida albicans and C. glabrata, in a single reaction?

<p>It allows for a faster and more efficient detection and identification process. (B)</p> Signup and view all the answers

In padlock probe technology, what is the immediate consequence if the probe perfectly matches the target DNA during hybridization?

<p>DNA ligase aids in forming a circular molecule. (B)</p> Signup and view all the answers

Why is the removal of non-hybridized templates important in padlock probe technology?

<p>To ensure that only correctly hybridized probes are amplified. (D)</p> Signup and view all the answers

In Hyperbranched Rolling Circle Amplification (H-RCA), what is the role of the two pre-designed primers in the absence of a circular molecule?

<p>They remain inactive, and no amplification occurs. (B)</p> Signup and view all the answers

What is the purpose of SYBR green in the context of real-time PCR monitoring of isothermal rolling circle amplification?

<p>To provide a fluorescent signal proportional to the amount of double-stranded DNA produced. (A)</p> Signup and view all the answers

In Loop-mediated Isothermal Amplification (LAMP), what is the significance of using a set of specifically designed primers targeting multiple regions of the target DNA?

<p>To enhance the specificity and efficiency of the amplification process. (A)</p> Signup and view all the answers

Which mechanism of action is associated with Echinocandin drugs like Caspofungin?

<p>Inhibition of β-glucan synthase, thereby blocking fungal cell wall synthesis. (D)</p> Signup and view all the answers

Amphotericin B disrupts fungal cell membranes by directly interacting with:

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

Azole antifungal drugs inhibit ergosterol synthesis by targeting which of the following?

<p>Cytochrome P450-dependent demethylation of lanosterol. (D)</p> Signup and view all the answers

Which antifungal drug inhibits DNA synthesis by acting as a nucleoside analogue?

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

What is the primary mechanism of action of Terbinafine?

<p>Inhibiting squalene epoxidase. (A)</p> Signup and view all the answers

Which of the following best describes the mechanism of action of Griseofulvin?

<p>It binds to tubulin, disrupting microtubule formation and inhibiting mitotic spindle formation. (D)</p> Signup and view all the answers

Why is Flucytosine typically used in combination with Amphotericin B?

<p>To prevent the rapid emergence of resistant mutants. (A)</p> Signup and view all the answers

Which of the following antifungal agents is LEAST likely to be administered systemically due to its high toxicity?

<p>Miconazole. (D)</p> Signup and view all the answers

Which of the following statements regarding antifungal resistance is MOST accurate?

<p>Fungi rarely develop resistance to Amphotericin B. (B)</p> Signup and view all the answers

Which antifungal agent is also active against protozoa?

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

Flashcards

Granulomas

Localized inflammatory response forming around pathogens like fungi.

Cell-mediated immune response

Immune mechanism involving immune cells to fight infections.

Delayed Hypersensitivity

An immune response that is slower and involves skin reactions.

Candida skin testing

A test to check for normal cell-mediated immunity using Candida antigens.

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Host defense against fungi

Mechanisms like intact skin and normal flora that protect against fungal infections.

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Respiratory tract defense

Mucous membranes and alveolar macrophages trap and destroy inhaled fungi.

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Circulating IgG and IgM

Antibodies produced in response to fungal infections, role in protection is unclear.

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Fungi-caused conditions

Fungi can lead to allergies, mycotoxicosis, and other infections.

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Fluorescent in situ hybridisation

A technique used to detect and localize specific RNA or DNA sequences in cells or tissues using fluorescent probes.

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DNA array hybridization

A method to measure the expression levels of multiple genes simultaneously by hybridizing DNA samples to an array of oligonucleotides.

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Multiplex tandem PCR

A PCR technique that enables simultaneous amplification of multiple DNA targets from a single sample.

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Padlock probe technology

A technique that uses circular probes to detect specific DNA sequences, allowing for high specificity in identifying targets.

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Rolling circle amplification

A method for amplifying DNA that generates long repeats of DNA sequences from a circular template.

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Schematic of padlock probe steps

Illustrates the process of padlock probes hybridizing and being amplified when a match occurs.

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Isothermal Systems

Methods like LAMP and padlock probes that amplify DNA without temperature cycling, maintaining constant temperature throughout.

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Loop mediated isothermal amplification (LAMP)

An isothermal amplification technique that is fast and highly specific, using loop primers to facilitate amplification at a constant temperature.

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Superficial Mycosis

Infections of the skin caused by fungi.

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Deep Mycosis

Fungal infections that affect internal organs.

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Mycotoxicoses

Diseases caused by ingested fungal toxins.

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Amanitin

A potent toxin that inhibits RNA polymerase.

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Aflatoxins

Carcinogenic toxins produced by Aspergillus flavus.

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Ergotism

A condition caused by ingesting ergot from infected grains.

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Allergy to Fungal Spores

Immediate hypersensitivity reaction to fungal spores.

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Immediate Hypersensitivity Response

Rapid allergic reaction mediated by IgE antibodies.

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Thermally Dimorphic Fungi

Fungi that change structure with temperature, mold in environment, yeast in human tissue.

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Obligate Aerobes

Fungi that require oxygen for survival; cannot grow in absence of oxygen.

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Facultative Anaerobes

Fungi that can survive with or without oxygen, switching modes based on environment.

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Heterotrophic Organisms

Organisms that depend on organic compounds for nutrition; cannot produce their own food.

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Zygospores

Large, thick-walled spores formed by sexual reproduction in fungi.

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Ascospores

Spores formed in a sac called ascus during sexual reproduction of fungi.

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Conidia

Asexual spores produced by fungi for propagation; important for identification.

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Fungi Imperfecti

Fungi that do not form sexual spores; classified separately due to lack of known sexual reproduction.

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LAMP

Loop-Mediated Isothermal Amplification; a technique for amplifying DNA.

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FIP and BIP primers

Forward Inner Primer (FIP) and Backward Inner Primer (BIP) that facilitate loop formation in LAMP.

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Final products of LAMP

Stem-loop DNAs with multiple inverted repeats and cauliflower-like structures with loops.

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Complement Fixation Test

A test used for diagnosing specific fungal infections like Coccidioidomycosis and Histoplasmosis.

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Antibody titer rise

A significant increase in antibody levels observed in systemic mycoses diagnosis.

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Amphotericin B

An antifungal drug that disrupts fungal cell membranes by targeting ergosterol.

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Azole drugs

A class of antifungals that inhibit ergosterol synthesis, essential for fungal membranes.

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Caspofungin

An antifungal that inhibits β-glucan synthesis in fungal cell walls.

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Echinocandins

Antifungal drugs inhibiting fungal cell wall synthesis by blocking β-glucan synthase.

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Flucytosine

Antifungal that inhibits DNA synthesis; used with Amphotericin B for cryptococcal infections.

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Terbinafine

Antifungal blocking ergosterol synthesis by inhibiting squalene epoxidase.

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Griseofulvin

Antifungal used for hair & nail infections, binds to tubulin to disrupt mitotic spindle.

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Pentamidine

Active against fungi and protozoa; used to prevent pneumonia by Pneumocystis jiroveci.

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Micafungin

Echinocandin approved for esophageal candidiasis and prophylaxis in bone marrow patients.

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Resistance to antifungals

Clinically significant resistance to antifungal drugs is uncommon but increasing for azoles.

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Study Notes

Mycology Lecture 1: General Characteristics of Fungi

  • Fungi are eukaryotic organisms, unlike prokaryotic bacteria.
  • They differ significantly in fundamental aspects, including cell structure.
  • Two crucial fungal cell structures are important medically:
  • The cell wall is primarily composed of chitin, unlike bacterial cell walls which contain peptidoglycan. This structural difference makes fungi resistant to antibiotics like penicillin that target peptidoglycan.
  • The fungal cell membrane contains ergosterol, distinct from the cholesterol present in human cell membranes.
  • Fungi have various roles, including food production (e.g., bread, cheese, wine) and the production of antibiotics; however, they can also cause food spoilage and diseases in humans, animals, and plants.
  • Examples of food produced using fungi include mushrooms.

Structure & Growth

  • Fungi exist in two primary forms:
  • Yeasts: single-celled organisms that reproduce asexually by budding.
  • Molds: long filamentous structures called hyphae that form a mat called a mycelium.
  • Some molds have hyphae that form transverse walls (septate hyphae), while others don't (nonseptate/coenocytic hyphae)

Classification

  • Fungi are classified based on their mode of nutrition:

  • Saprophytic fungi feed on dead organic matter (e.g., Rhizopus, Penicillium, Aspergillus).

  • Parasitic fungi feed on living organisms (e.g., Taphrina, Puccinia).

  • Symbiotic fungi have interdependent relationships with other species (e.g., lichens, mycorrhizae).

  • Lichens are a symbiotic association of algae and fungi.

  • Mycorrhizae are another symbiotic relationship between fungi and plant roots to enhance nutrient uptake by the plants

  • Fungi are further classified based on spore formation (e.g., zygospores, ascospores, basidiospores)

  • Fungi that don't form sexual spores are called "imperfect" fungi.

  • Morphology of fungi (shape, color, arrangement of conidia) can be used in identification.

Pathogenesis

  • Fungi cause diseases in humans via several pathological mechanisms:

  • Granulomas are a key feature in several systemic fungal diseases (i.e., coccidioidomycosis, histoplasmosis, blastomycosis).

  • Cell-mediated immune responses are critical in granuloma formation.

  • Acute suppuration (neutrophil presence) can also be observed in systemic fungal infections.

  • Fungal pathogenicity is not associated with endotoxins or bacterial-type exotoxins, unlike bacterial infections.

  • Positive skin tests can indicate prior exposure and not active infection.

Laboratory Diagnosis

  • Microscopic examination, fungal culture, DNA probe tests, and serological tests are used for diagnosis
  • Methods like Potassium Hydroxide help dissolve other tissues to identify structures like spherules (Coccidioides), capsules (Cryptococcus). Stains are used for visualizing fungal structures in tissue specimens.
  • Sabouraud's agar is effective and commonly used to cultivate and identify slow-growing fungi, inhibiting bacterial growth.
  • DNA probe tests are fast methods in detecting fungal colonies.
  • Serologic testing is used to detect the presence of antibodies against fungi.

Antifungal Therapy

  • Drugs used to treat bacterial infections are often ineffective against fungi.

  • This is due to the different cellular structures present on each organism (e.g. peptidoglycans in bacteria).

  • Different drugs target fungal cell wall synthesis, fungal cell membrane, or fungal DNA synthesis:

  • Echinocandins (e.g., Caspofungin): block fungal cell wall synthesis.

  • Polyenes (e.g., Amphotericin B and Nystatin): disrupt fungal cell membranes.

  • Azoles (e.g., Fluconazole, Itraconazole): inhibit ergosterol synthesis.

  • Flucytosine: inhibits fungal DNA synthesis.

  • Resistance to antifungals is an infrequent situation but increasing, notably azoles résistance.

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