MEDICAL MYCOLOGY

Dr Tadayo Hashimoto M.D.
Professor
Department of Microbiology & Immunology

DIRECTIONS: Each of the numbered items or incomplete statements is followed by answers or by completions of the statement. Select the ONE lettered answer or completion that is BEST in each case. You may click answer and explanation button to find out whether answer you select is correct, and if not, why.

REFERENCE

Joklik WK, Willett HP, Amos DB, Wilfert CM. Zinsser Microbiology. 20th ed. Norwalk, Conn: Appleton & Lange; 1992.

Ryan KJ, Champoux JJ, Drew WL, Falkow S, Neidhardt FC, Plorde JJ, and Ray CG. Sheriis Medical Microbiology. 3rd ed. Norwalk, Conn: Appleton & Lange, 1994.

Fungi:
1. are prokaryotic cells
2. are susceptible to certain antibacterial antibiotics
3. are Gram positive microorganisms
4. are, in general, smaller than bacteria
5. contain either DNA or RNA, not both.
Answer and explanation
Dimorphism in fungi refers to:
1. the ability of fungi to produce two types of spores
2. the characteristic of certain fungi to develop male and female hyphae in one colony
3. the ability of fungi to grow in two different forms, yeast and mycelial, depending on environmental conditions
4. the ability of fungi to undergo mitosis as well as meiosis
5. the property of fungi to develop spherical and elongated forms of nuclei
Answer and explanation
All of the following statements about fungal growth are true EXCEPT that:
1. hyphae result from continuous apical extension
2. all fungi, except for those belonging to the class zygomycetes, are septated
3. budding is a common reproductive mechanism of yeast cells
4. entangled masses of individual hyphae are called mycelium
5. only the yeast form of fungi produces sexual spores
Answer and explanation
All of the following statements concerning fungal spores are true EXCEPT that:
1. a conidium is an asexually formed fungal spore
2. in the majority of fungi pathogenic to humans, sexual cycles of spore formation are not demonstrated
3. morphologic characteristics of conidia are a useful aid for the identification of fungi
4. fungal spores are as resistant to heat as bacterial spores
5. fungal spores cause allergies in some people
Answer and explanation
The cell walls of most fungi:
1. are the target of penicillin action
2. contain teichoic acid and peptidoglycan
3. contain chitin and ß-1 : 3-linked glucan
4. lack antigenicity
5. contain sterols
Answer and explanation
Mycotic infections
1. can be diagnosed without isolation of a causative agent.
2. usually need no medication because they tend to heal spontaneously
3. are opportunistic infections
4. do not resemble to bacterial infections in their clinical manifestations
5. are one of the most frequent complications that kill AIDS patients
Answer and explanation
All of the following statements are true EXCEPT that
1. aflatoxins are produced by Aspergillus flavus and have been implicated in human liver cancer
2. amatoxins and phallotoxins are produced by poisonous mushrooms
3. amatoxins and phallotoxins interfere with messenger RNA functions in the liver
4. mycotoxicosis can be treated with sera containing specific antitoxins
5. heating has essentially no effect on reducing the toxicity of mycotoxins
Answer and explanation
Dermatophytosis is a fungal skin infection that:
1. is caused by one specific species of fungus
2. often spreads to the subcutaneous tissues or deep-seated organs
3. should be treated with amphotericin B
4. is rarely transmitted from human to human
5. is often fatal
Answer and explanation
The characteristics of zygomycoses (synonyms: mucormycosis and phycomycosis) include all of the following EXCEPT that:
1. the causative fungi often invade capillary blood vessels, producing occlusion of the vessels
2. they are highly transmissible from person to person
3. infections occur mostly in compromised hosts
4. septa are absent in hyphae of the causative agents
5. the central nervous system is often involved
Answer and explanation
Conditions often underlying opportunistic fungal infections include all of the following EXCEPT:
1. use of broad-spectrum antibacterial antibiotics for extended periods
2. therapeutic use of immunosuppressive drugs
3. therapeutic use of radiation
4. loss of T-helper-cell functions due to human immunodeficiency virus infections
5. all of the above
Answer and explanation
Which of the following statements concerning Coccidioides immitis and coccidioidomycosis is NOT correct?
1. infections usually occur through the inhalation of arthroconidia
2. spherules are formed in infected tissues and are considered to be of diagnostic value
3. the coccidioidin test is useful in the diagnosis of the infection
4. amphotericin B is the drug of choice in the treatment
5. arthroconidia are found in the soil of any state in the United States
Answer and explanation
Coccidioidomycosis is:
1. transmitted from person to person via air-borne spherules
2. by and large an inapparent and self-limited infection in endemic areas
3. best treated with griseofulvin
4. most prevalent in the southeastern region of the United States
5. diagnosed by demonstrating arthroconidia formed in vivo
Answer and explanation
Acquired resistance to coccidioidomycosis is demonstrated by:
1. elevated levels of humoral antibody
2. an immediate wheal reaction following an intradermal injection of coccidioidin
3. a positive tuberculin reaction
4. delayed hypersensitivity to coccidioidin
5. a negative reaction to coccidioidin
Answer and explanation
A leukemic patient complains of respiratory symptoms including frequent coughs. X-ray examination of the left lung reveals the presence of a coin-sized lesion characterized by the presence of an air space surrounding the cavity. Sputa of the patient show the presence of thick and uniformly septate hyphae. The culture of sputa yields hairy colonies firmly adhering to the agar surface. The patient _Fs tuberculin test is negative. The most likely cause of the respiratory problem of this patient is:
1. tuberculosis
2. mucormycosis
3. aspergillosis
4. histoplasmosis
5. candidiasis
Answer and explanation
The binding of polyene antibiotics to the cytoplasmic membrane of fungi causes:
1. the initiation of cell division
2. blocking of protein synthesis
3. accumulation of intracellular K+
4. loss of mitochondria
5. loss of intracellular K+
Answer and explanation
All of the following statements concerning the pathogenicity of fungi are true EXCEPT that:
1. Only a small number of fungi are able to cause diseases in previously healthy persons
2. Most fungi are readily killed by neutrophils
3. No exotoxin or endotoxin is involved in fungal pathogenesis
4. T-cell mediated responses are not important in the development of immunity to fungal infections
5. For some fungi, the capsule is an important pathogenic factor
Answer and explanation
Pneumocystis carinii:
1. infection should be treated with trimethoprim-sulfamethoxazole
2. is a strict pathogen
3. in infected tissues can not be detected by any stains
4. can be cultured on blood agar
5. can be treated effectively by ketoconazole
Answer and explanation
Azole antifungal agents such as ketoconazole and itraconazole:
1. are metabolites of bacteria
2. interfere with the biosynthesis of ergosterol in susceptible fungi
3. should never be given orally
4. are similar to polyene antibiotics in their mode of action
5. are indicated only for dermatophytosis
Answer and explanation
A female patient who participated in an archeological excavation of Indian ruins in the southwestern region of the United States complains of severe systemic and respiratory symptoms. Her skin coccidioidin test is positive. The titers of complement-fixing antibody are as follows:
Day 15 after exposure 1 : 8
Day 21 after exposure 1 : 16
Day 28 after exposure 1 : 64

You may predict that she:
1. will recover soon because high complement fixation does not correlate with the severity of infection
2. may have active disseminated coccidioidomycosis
3. can be released soon because high levels found in the complement fixation test mean high immunity
4. may not need amphotericin B treatment
5. none of the above
Answer and explanation
A healthy middle-aged construction worker who engaged in a demolition task 10 days ago complains of respiratory symptoms similar to those of pneumonia. No causative agents are successfully isolated from his sputa. The patient does not respond to any antibacterial antibiotics and dies before a definitive diagnosis was established. Microscopic examination of specimens taken from granulomatous and suppurative lesions of the lung obtained during necropsy reveals the presence of large budding yeast cells. The bud is attached to the parent cell by a broad base. Based on this data, you diagnose the disease of this patient as:
1. histoplasmosis
2. coccidioidomycosis
3. cryptococcosis
4. blastomycosis
5. sporotrichosis
Answer and explanation
A male gardener sustains a minor scratch on his forearm while working in a thorny rose garden. A couple of weeks later, the wound progressively develops into granulomas involving the draining lymphatics. Although the wound does not spread beyond the subcutaneous tissues, it fails to respond to antibacterial antibiotic treatments. Microscopic examination of the exudates obtained from infected areas reveals the presence of yeast cells that assume a cigar shape. Cultures of aspirated fluids from the infected areas result in the isolation of a dimorphic fungus that grows yeast at 35°C and hyphae at 25°C. The most likely diagnosis of this infection is:
1. chromomycosis
2. histoplasmosis
3. sporotrichosis
4. coccidioidomycosis
5. blastomycosis
Answer and explanation
All of the following statements concerning chromomycosis are correct EXCEPT that it:
1. is caused by a group of dermatiaceous fungi that produce melanin-like pigments
2. is a deep-seated systemic mycotic infection
3. is most often caused by traumatic implantation
4. is characterized by granulomatous nodules and epithelial hyperplasia
5. affects both immunocompetent and immuno-compromised individuals
Answer and explanation
Flucytosine:
1. is effective against filamentous fungi
2. can not be administered orally
3. can be used without worrying about the development of resistance to the drug
4. is converted to 5-fluorouracil which can be incorporated into fungal RNA or serves as inhibitors of thymidylate synthetase
5. should not be used in combination with amphotericin B
Answer and explanation
Histoplasmosis and tuberculosis share the following characteristics EXCEPT that:
1. causative agents can survive within resident macrophages
2. infection elicits a delayed-type hypersensitivity skin reaction to appropriate antigens
3. pulmonary infections often leave calcified lesions
4. most infections are clinically inapparent
5. they can be treated by rifampin, streptomycin, and pyrazinamide
Answer and explanation
A 65-year-old female patient is admitted to an intensive care unit because of a sudden swelling of the right side of the face and an episode of bleeding from the right nostril. According to her daughter, these signs were not apparent a few days ago. She has a long history of diabetes and high blood pressure and recently developed clinical signs of ketoacidosis and renal insufficiency. Her blood sugar level at the time of admission is 700 mg/dL. The facial lesion becomes partially necrotic and shows slight protrusion of the right eye and facial paralysis. The patient dies on the second day. Histopathologic examination of the lesions reveals occlusion of small vessels and the presence of non-septate hyphae. This is most probably caused by:
1. candidiasis
2. nocardiosis
3. mucormycosis
4. erysipelas
5. gas gangrene
Answer and explanation

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Last Reviewed: Apr 15, 2006
Created: Aug 2, 1996