Ch 21 Mycology

MLT 142 Unit 2 Ch 21 Mycology

Fungal infections are generally acquired via which route?

Inhalation of spores

Fungal infections are generally not communicable in the usual sense of person-to-person transmission. Humans become an accidental host for fungi by inhaling spores or by the introduction of fungal elements into tissue by trauma.

An example of a dimorphic fungus is:

Coccidioides immitis

The medically important dimorphic fungi include Histoplasma capsulatum, Blastomyces dermatitidis, C. immitis, Paracoccidioides brasiliensis, Sporothrix schenckii, and Talaromyces marneffei

A 16-year-old male teenager is diagnosed with a fungal infection of his foot, which he acquired at the gym. This infection would most likely be classified as a(n) _______ mycosis.

Superficial

The condition is most likely athlete’s foot caused by a dermatophyte. The superficial, or cutaneous, mycoses are fungal infections that involve the hair, skin, or nails without direct invasion of the deeper tissue. The fungi in this category include the dermatophytes—agents of ringworm, athlete’s foot, and others—and agents of infections such as tinea, tinea nigra, and piedra. All of these infect keratinized tissues.

A 59-year-old patient with cancer who was receiving high doses of chemotherapy developed a secondary lung infection that was identified as a fungus. The organism disseminated, which ultimately was fatal to the patient. The organism isolated from sputum exhibited septate hyphae that were dichotomous. The organism is most likely which of the following?

Aspergillus

Infections primarily occur in patients with some type of compromise to their immune system. The infection may be secondary to an underlying disease process, such as diabetes mellitus, or the result of an immunosuppressive agent. Although any fungus can potentially cause disease in these patients, the most commonly encountered organisms in this group include Aspergillus Candida, and Cryptococcus, among others. All of these organisms may cause disseminated (systemic) disease. Aspergillus, however, exhibits septate hyphae that are dichotomous.

A 29-year-old patient with acquired immunodeficiency syndrome (AIDS) is suspected of having a Cryptococcus spp. infection in the cerebrospinal fluid (CSF). A CSF specimen is collected and set up on cycloheximide agar. In addition, an India ink stain is set up. The India ink stain reveals encapsulated yeast; however, 3 weeks later, the cycloheximide agar is negative. Which one of the following statements explains this discrepancy?

The ingredients in the cycloheximide agar most likely inhibited the growth of the organism.

Cycloheximide may be added to any of the media that contain or lack antibacterial antibiotics. However, if cycloheximide is included in the battery of culture media, then a medium lacking this ingredient should also be included. Pathogenic fungi, such as Cryptococcus, Candida krusei, other Candida spp., Pseudallescheria boydii, and Aspergillus spp., are partially or completely inhibited by cycloheximide.

If a fungal colony is described as rugose, then it means that the colony:

furrows radiate out from the center

Topography can be described as verrucose (furrowed or convoluted), umbonate (slightly raised in the center), and rugose (furrows radiate out from the center).

Microscopically, this fungus appears barrel shaped with thick walls, which best describes which type of conidia?

Arthroconidia

Arthroconidia are formed directly from the hyphae by fragmentation through the points of septation. When mature, they appear as square, rectangular, or barrel-shaped thick-walled cells. These are a result of the simple fragmentation of the hyphae into spores, which are easily dislodged and disseminated into the environment.

All mold cultures and clinical samples should always be handled in a Class _____ level biosafety cabinet.

II

A septate hyphae is microscopically observed using lactophenol cotton blue. Which organism can be ruled out as the cause of infection on the basis of this information?

Rhizopus

Rhizopus is the only organism listed that has aseptate hyphae (Table 58-3).

The mode of transmission for most of the dimorphic fungi is:

inhalation

The majority of the dimorphic fungi are transmitted via the inhalation of spores. Trauma is another portal of entry of the organism.

Which stain requires the use of a fluorescent microscope?

Calcofluor white

Calcofluor white requires a fluorescent microscope, whereas the other stains do not.

A 28-year-old woman was gardening when a rose thorn pricked her finger, which later became infected. A sample is taken of the exudate and sent to the microbiology laboratory. Small, round, cigar-shaped structures are microscopically observed. She is most likely infected with which type of fungi?

S. schenckii

Small, round, cigar-shaped structures describe the morphologic appearance of S. schenckii, which is associated with gardening since the organism is found in the soil.

A capsule and phenoloxidase melanin synthesis are virulence factors contributing to the pathogenicity of which of the following organisms?

Cryptococcus spp.

A capsule and phenoloxidase melanin synthesis are both virulence factors of Cryptococcus.

Organisms that cannot be differentiated to the species level using phenotypic, physiological or biochemical means and are indistinguishable clinically are considered:

molecular siblings

Organisms that cannot be distinguished or speciated based on phenotypic, metabolic and clinical presentations but are recognized as different species based on molecular analysis are considered a molecular sibling

Direct detection of yeast in blood stream infections is problematic due to:

low numbers of organisms present in the sample.

blood proteins cause erroneous spectra and failed identification

hemoglobin interferes with spectral patterns

The level of fungal organisms, such as yeast in the blood stream and other clinical fluid samples is generally too low for direct detection by MALDI-TOF MS. In addition, proteins and hemoglobin tend to interfere with the spectra analytics making identification problematic

Unbranched sporangiophores with rhizoids that appear opposite the point where the stolon arises at the base of the sporangiophore best describes which zygomycetes?

Rhizopus

Rhizopus has unbranched sporangiophores with rhizoids that appear opposite the point where the stolon arises at the base of the sporangiophore. In contrast, Mucor is characterized by sporangiophores that are singularly produced or branched and have a round sporangium at the tip filled with sporangiospores. It does not have rhizoids or stolons, which distinguishes it from the other genera of zygomycetes. Lichtheimia, an uncommon isolate in the clinical laboratory, is characterized by the presence of rhizoids that originate between sporangiophores.

Which genus is involved in infections of the skin and nails only?

Epidermophyton

The genus Trichophyton is capable of invading the hair, skin, and nails, whereas the genus Microsporum involves only the hair and skin; the genus Epidermophyton involves the skin and nails.

The term used to describe ringworm of the nail is:

Tinea unguium

Cutaneous mycoses are perhaps the most common fungal infections of humans and are usually referred to as tinea (Latin for worm or ringworm). Examples include Tinea corporis, which is ringworm of the body; Tinea cruris, which is ringworm of the groin (“jock itch”); Tinea capitis, which is ringworm of the scalp and hair; Tinea barbae, which is ringworm of the beard; Tinea unguium, which is ringworm of the nail; and Tinea pedis, which is ringworm of the feet (“athlete’s foot”).

The slow-growing organism Trichophyton rubrum produces a flat or heaped-up colony, generally white to reddish with a cottony or velvety surface. The cherry-red color is best observed on the reverse side of the colony. This organism is capable of infecting which of the following?

Hair, skin, and nails

T. rubrum is a slow-growing organism that infects hair, skin, and nails. T. rubrum produces a flat or heaped-up colony, generally white to reddish with a cottony or velvety surface. The characteristic cherry-red color is best observed on the reverse side of the colony; however, this color is produced only after 3 to 4 weeks of incubation.

A hair perforation test is performed using Trichophyton mentagrophytes and T. rubrum. The expected results are:

positive for T. mentagrophytes and negative for T. rubrum.

T. mentagrophytes produces urease within 2 to 3 days after inoculation onto Christensen’s urea agar. In contrast to T. rubrum, T. mentagrophytes perforates hair (Figure 59-10). This latter criterion may be used when distinguishing these two species is difficult.

Which dermatophyte usually fluoresces yellow-green under a Wood’s lamp?

Microsporum audouinii

M. audouinii was, in past years, the most important cause of epidemic Tinea capitis among schoolchildren in the United States. This organism is anthropophilic and is spread directly by means of infected hairs on hats, caps, upholstery, combs, or barber clippers. The majority of infections are chronic; some heal spontaneously, whereas others may persist for several years. Infected hair shafts fluoresce yellow-green using a Wood’s lamp.

A fungus is recovered from a nail scraping. Microscopic examination reveals numerous smooth, thin-walled, club-shaped, multiseptate macroconidia; however, microconidia are absent. The organism can be identified as:

E. floccosum

E. floccosum grows slowly, and growth appears as an olive green-to-khaki color, with the periphery surrounded by a dull orange-brown color. After several weeks, colonies develop a cottony white aerial mycelium that completely overgrows the colony and is sterile; it remains so, even after subculture. Microscopically, numerous smooth, thin-walled, club-shaped, multiseptate (2 to 4 µm) macroconidia are observed. They are rounded at the tip and are borne singly on a conidiophore or in groups of two or three. Microconidia are absent, spiral hyphae are rare, and chlamydoconidia are usually numerous.

A pulmonary fungus ball and external otomycosis and onychomycosis are all infections caused by which genera?

Aspergillus

Aspergillus spp. are capable of causing disseminated infection, as observed in patients who are immunocompromised, but are also capable of causing a wide variety of other types of infections, including a pulmonary or sinus fungus ball, allergic bronchopulmonary aspergillosis, external otomycosis (i.e., a fungus ball of the external auditory canal), mycotic keratitis, onychomycosis (i.e., infection of nail and surrounding tissue), sinusitis, endocarditis, and central nervous system infection. Most often, patients who are immunocompromised acquire a primary pulmonary infection that rapidly becomes progressive and may disseminate to virtually any organ

Which rapidly growing Aspergillus spp. (2 to 6 days) best describes a mold that produces a fluffy-to-granular, white-to-blue green colony?

A. fumigatus

A. fumigatus is a rapidly growing mold (2 to 6 days) that produces a fluffy-to-granular, white-to-blue green colony. Mature sporulating colonies most often exhibit the blue-green powdery appearance.

Which organism produces mostly shades of green or blue-green colonies? Microscopically, hyphae are hyaline and septate and produce brushlike conidiophores

Penicillium

Colonies of Penicillium are most commonly shades of green or blue-green, but pink, white, or other colors may also be observed. The surface of the colonies may be velvety to powdery because of the presence of conidia. Microscopically, hyphae are hyaline and septate and produce brush-like conidiophores (i.e., a penicillus).

A patient presents with a pulmonary infection that demonstrates large granulomas in the lung. Histological examination identified the presence of budding yeast and adiaspores. The most likely identification of the etiologic agent is:

Emmonsia

Emmonsia spp. produces a self-limited, localized pulmonary infection that may appear asymptomatic. Diagnosis is generally incidentally to other underlying conditions. The organism produces adiaspores which enlarge but do not reproduce in the patient. Emergomyces spp. produce budding yeast cells but do not demonstrate adiaspores and often develops into a systemic disorder with widespread cutaneous lesions. Nucleic-acid sequencing may be required to speciate and differentiate these organisms.

Dermatophytes that are contracted by exposure to contaminated soil or animals is considered:

geophilic and zoophilic

Dermatophytes are transmitted through various routes including species are anthropophilic, or “human loving” and found on the skin of individuals; few are zoophilic, primarily infecting animals and associated with contact with animals or geophilic, soil associated.

An agricultural worker is punctured by a tool used in the field. An infection, characterized by the development of a papule that is similar to a cauliflower appearance, develops. The worker is most likely suffering from which type of infection?

Chromoblastomycosis

Chromoblastomycosis is a chronic fungal infection acquired via the traumatic inoculation of an organism, primarily into the skin and subcutaneous tissue. The infection is characterized by the development of a papule at the site of the traumatic insult that slowly spreads to form warty or tumorlike lesions characterized as similar in appearance to cauliflower

In general, yeast reproduces asexually by the formation of:

blastoconidia

In general, yeast reproduces asexually by blastoconidia formation (budding) (Figure 62-1) and s*xually by the production of ascospores or basidiospores.

The most commonly isolated yeast in clinical specimens is:

Candida albicans

Candida infections are caused by a variety of species. Although C. albicans is the most commonly isolated yeast, other species are emerging such as Candida glabrata, Candida parapsilosis, C. tropicalis, C. dubliniensis, and C. krusei. The frequency with which these are isolated varies by institution.

Cryptococcus neoformans is widely distributed in nature, and aerosolization is a prerequisite to most infections. This organism is most often associated with exposure to:

pigeon excreta

C. neoformans exists as a saprobe in nature and is most often found associated with avian excreta, particularly that of pigeons. Numerous reports substantiate the hypothesis that pigeon habitats serve as reservoirs for human infection. The pigeon manure apparently serves as an enrichment factor for C. neoformans because of its composition. C. neoformans is believed to be widely distributed in nature, and aerosolization is a prerequisite to most infections

A patient with diabetes is experiencing creamy patches on his tongue and mucous membranes. Cultures are performed, and yeast is recovered. His diagnosis is most likely

thrush

Thrush is an infection of the mucous membranes in the mouth and is considered a localized infection. Thrush can be observed in newborns, in patients with human immunodeficiency virus or diabetes, and in patients who are receiving chemotherapy. Creamy patches or colonies will appear on the tongue and mucous membranes. Candida may be recovered from the oropharynx, gastrointestinal tract, genitourinary tract, and skin.

A patient with leukemia is diagnosed with a Candida infection after receiving several doses of chemotherapy. The most likely yeast causing the infection is

C. tropicalis

C. tropicalis has been shown to be prevalent in patients with hematologic malignancies, especially those with neutropenia

A fungal infection found mostly in the tropics and temperate regions is characterized by the development of soft, yellow or pale-brown aggregations around hair shafts in the axillary, facial, genital, and scalp regions. The fungus that would most likely be isolated is:

Trichosporon

White piedra caused by Trichosporon spp. is an uncommon fungal infection in patients who are immunocompetent and is found in both tropical and temperate regions of the world. It is characterized by the development of soft, yellow or pale-brown aggregations around hair shafts in the axillary, facial, genital, and scalp regions of the body. The Trichosporon spp. that causes this disease frequently invades the cortex of the hair and causes damage

Tinea versicolor is a skin infection characterized by superficial brownish scaly areas most often on the trunk, arms, or shoulders. Which type of replacement therapy places patients at risk for developing this type of skin infection?

Lipid

Malassezia furfur is the most common cause of tinea versicolor, a skin infection that is characterized by superficial brownish scaly areas on light-skinned persons and lighter areas on dark-skinned persons. The lesions occur on the smooth surfaces of the body, specifically, the trunk, arms, shoulders, and face. It has a worldwide distribution. M. furfur is also a cause of disseminated infection in infants and young children as well as in adults taking lipid replacement therapy.

Encapsulated yeast is identified in the cerebrospinal fluid (CSF) of a patient with AIDS. The most likely stain or reagent used to identify this organism is:

India ink

Traditionally, the India ink preparation has been the most widely used method for the rapid detection of C. neoformans in clinical specimens. This method delineates the large capsule of C. neoformans, because the ink particles cannot penetrate the capsular polysaccharide material

Agar medium overlaid with olive oil will enhance the growth of which organism?

Malassezia

Malassezia spp. is infrequently cultured in the clinical laboratory. Cultivation, for example, from a positive blood culture requires an agar medium overlaid with a long-chain fatty acid (olive oil). The colonies are small when compared with the colonies of C. albicans and are creamy and white to off white.

Blood cultures are drawn on a patient suspected of having a fungemia. Positive cultures reveal the presence of chlamydoconidia on cornmeal agar. In addition, the yeast is germ tube positive. The most likely identification of the fungal agent is:

C. albicans

One method of identification of C. albicans and the differentiation from other Candida spp. is made on the basis of the presence of chlamydoconidia (Figure 62-11) on cornmeal agar containing 1% Tween 80 and trypan blue incubated at room temperature for 24 to 48 hours

Determining urease activity and growth on niger seed agar is helpful in determining which type of yeast?

C. neoformans

The rapid urease test (Procedure 62-2) is a most useful tool for screening for urease-producing yeast recovered from respiratory secretions and other clinical specimens. An alternative to traditional urease testing is the rapid selective urease test (Procedure 62-3). This method appears to be useful in rapidly detecting C. neoformans. Using these screening tests is helpful to make a presumptive identification of C. neoformans. In instances in which inoculum is limited, the laboratorian must use tests that can be performed and then prepare a subculture so that additional tests can be performed later. Often, inoculating the organism onto the surface of a plate of niger seed agar is just as fast; the results may be obtained during the same day of incubation at 25°C. This is discussed further in this section.

Which of the following is used in superficial fungal infections to dissolve the skin, hair, or nails so that the fungal structures can be observed?

KOH

Which of the following stains is used to visualize fungal structures in tease preparations and slide cultures?

Lactophenol cotton blue

One drawback of using SDA with cycloheximide and chloramphenicol is that

Cryptococcus and other yeast may be inhibited

Macroscopic growth characteristics of the fungi include

A) topography.

B) texture.

C) pigmentation

Which dermatophyte typically produces two- to four-celled smooth, club-shaped macroconidia, but does not produce microconidia?

Epidermophyton

Dematiaceous fungi

are pigmented brown to black

Which of the following fungi associated with subcutaneous fungal infections is also considered to be a dimorphic fungus?

Sporothrix schenckii

Dimorphic fungi with rectangular arthrospores

produce large, round, thick-walled spherules with endospores in the tissue phase.

The most outstanding characteristic of Candida albicans is its

production of germ tubes

Vegetative hyphae

absorb nutrients and water for the fungus

Small, oval, intracellular yeast cells appearing in Giemsa-stained preparations of bone marrow or peripheral blood should most likely be worked up as:

Histoplasma capsulatum

An agent of chromoblastomycosis that is a very slow-growing, black-olive or gray mold and that microscopically produces dark, septate hyphae with primary conidia forming at the tip of the conidiophore with secondary and tertiary conidia is most likely:

Fonsecaea pedrosoi

Which of the following is characterized by aseptate hyphae, stolons with rhizoids, and sporangiophores giving rise to sporangia in an internodal attachment?

Lichtheimia

Which atypical fungus, originally classified as a protozoan parasite, is a cause of pneumonia in the immunosuppressed, especially those with HIV-AIDS?

Pneumocystis jiroveci

Characteristics of Candida auris include all of the following, except:

A) asymptomatically colonizes patients.

B) usually susceptible to fluconazole and most first-line antifungal treatments.

C) oval to elongated budding yeast.

D) can tolerate high salt concentrations and temperatures of 40ºC to 42ºC.

Tinea pedis refers to ringworm of the _____.

foot

A chronic granulomatous infection of the tissue and bone with draining sinuses is known as a(n) _____

mycetoma

Dimorphic fungi exhibit a(n) _____or tissue phase at 35ºC to 37ºC

yeast

Thick-walled resistant spores that represent enlarged terminal hyphae are known as ______

chlamydospores/conidia

The primary isolation media for fungi is ______ dextrose agar

SAB/Sabourau/SDA

True or false? Zoophilic fungal infections are transmitted through contact with an infected animal.

True

True or False? Trichophyton species can infect the skin and hair, but not the nails

False

True or False? The agent of Black Piedra is Trichosporon beigelii

False

True or False? The Mucormycetes  produce septate hyphae

False

True or False? Cryptococcus is an encapsulated yeast that is urease positive

True