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NBME Micro > Microbiology: Mycology > Flashcards

Microbiology: Mycology Flashcards

1
Q

How is Pneumocystis pneumonia diagnosed?

A

From a bronchoalveolar lavage or lung biopsy; sample stained with methenamine silver or identified with a fluorescent antibody

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2
Q

A woman has a fungal infection that produces aflatoxins. For what condition should this patient periodically be monitored?

A

Hepatocellular carcinoma (Aflatoxins, produced by some Aspergillus species, are associated with this malignancy)

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3
Q

How do you treat disseminated systemic mycoses?

A

Amphotericin B

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4
Q

What region is blastomycosis endemic to?

A

Eastern or central United States, Great Lakes

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5
Q

How is histoplasmosis generally acquired?

A

Inhalation from bird (eg, starling) or bat droppings

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6
Q

How do Histoplasma, Blastomyces, Coccidioides, and Paracoccidioides organisms compare in terms of size to an RBC?

A

Histoplasma organisms are smaller; Blastomyces organisms are the same size; Coccidioides and Paracoccidioides organisms are larger

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7
Q

A man with diabetes mellitus has a headache, facial pain, a black necrotic facial eschar, and cranial nerve palsies. What might cause his cranial nerve palsies?

A

Cavernous sinus thromboses, a possible complication of Mucor and Rhizopus infections

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8
Q

How does Aspergillus fumigatus appear on culture media at 37°C?

A

45° branching septate hyphae with conidia radiating from the ends of conidiophores (broom-like appearance)

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9
Q

A 70-year-old patient is diagnosed with coccidioidomycosis pneumonia subsequently develops persistent headache and blurry vision. What condition should he be evaluated for?

A

Meningitis; as coccidioidomycosis can result in meningitis

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10
Q

How do you treat disseminated candidiasis?

A

Amphotericin B, fluconazole, or echinocandins

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11
Q

What treatment options are available for Aspergillus infections?

A

Voriconazole, echinocandins (2nd line)

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12
Q

Pathologically, how are systemic mycoses and tuberculosis similar?

A

Both can form granulomas

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13
Q

An immunocompromised patient presents with “soap bubble” lesions in his brain on imaging. How does this infection most likely develop?

A

Cryptococcus neoformans spreads to the CNS (usually meninges) through hematogenous dissemination after inhalation

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14
Q

A man has multiple erythematous scaling rings with central clearing. Where are these rings typically found?

A

On the torso; he likely has tinea corporis infection (ringworm)

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15
Q

At what CD4+ count should patients who are HIV+ begin to receive prophylaxis against Pneumocystis pneumonia?

A

< 200 cells/mm3

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16
Q

How do Mucor and Rhizopus proliferate in the body and cause infection?

A

The fungi grow in the blood vessels and enter the brain via the cribriform plate

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17
Q

All systemic mycoses can primarily cause what type of illness?

A

Pneumonia; all can disseminate

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18
Q

What class of organisms causes tinea pedis, cruris, corporis, capitis, and unguium?

A

Dermatophytes (representative geni include Microsporum, Trichophyton, Epidermophyton)

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19
Q

Which group of hosts would be symptomatic if infected with Pneumocystis?

A

Immunocompromised patients (eg, those with AIDS); otherwise, most are asymptomatic

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20
Q

A gardener presents with a pustule on her forearm and multiple nodules tracing upward toward her axilla. What is the most likely diagnosis?

A

Sporotrichosis (rose gardener’s disease)

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21
Q

How do Mucor and Rhizopus enter the body?

A

Via inhalation of spores

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22
Q

How is sporotrichosis treated?

A

Itraconazole or potassium iodide (for cutaneous/lymphocutaneous disease)

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23
Q

An athlete has hypopigmented and hyperpigmented macules on her back after intensive summer training. What is the most likely diagnosis?

A

Tinea (pityriasis) versicolor (Malassezia spp, Pityrosporum spp)

24
Q

How are Mucor and Rhizopus infections with brain involvement treated?

A

Surgical debridement and amphotericin B or isavuconazole

25
Q

What populations are more likely to develop invasive aspergillosis?

A

Patients who are immunocompromised and those with disorders of neutrophil dysfunction (ie, chronic granulomatous disease)

26
Q

How does tinea versicolor cause discolored patches on skin?

A

Lipid degradation by Malassezia spp (Pityrosporum spp) produces acids→inhibit tyrosinase (melanin synthesis)→hypopigmentation; inflammatory responses→hyperpigmentation/pink patches

27
Q

Name 3 infections caused by Cryptococcus neoformans typically found in immunocompromised patients

A

Cryptococcosis, cryptococcal encephalitis, and cryptococcal meningitis

28
Q

What region is Coccidioidomycosis endemic to?

A

Southwestern United States and California

29
Q

What is the first-line treatment for oral thrush alone?

A

Treatment for superficial Candida infections is nystatin, fluconazole, or echinocandins

30
Q

What exposure is most strongly associated with coccidioidomycosis infection?

A

Dust exposure in endemic areas (eg, after earthquakes or during excavations)

31
Q

What fungal infection are patients with TB at risk for due to their cavitary lesions?

A

Aspergillus fumigatus, which may cause aspergillomas in preexisting lung cavities (especially those from TB)

32
Q

How is sporotrichosis transmitted?

A

Introduction of fungal spores into the skin after an injury, often caused by thorns (hence, rose gardener’s disease)

33
Q

Paracoccidioidomycosis presents most similarly to which other systemic fungal disease?

A

Blastomycosis

34
Q

Which 2 groups of patients are most likely to develop ABPA (allergic bronchopulmonary aspergillosis)?

A

Patients with asthma and cystic fibrosis

35
Q

What is observed when the causative organism of diaper rash is grown at 37°C?

A

Germ tube formation at 37°C, which is diagnostic for Candida albicans

36
Q

What structure must Mucor and Rhizopus penetrate to invade the brain?

A

Cribriform plate

37
Q

How do TB and the systemic mycoses differ in transmission?

A

Only TB can be transmitted from person to person

38
Q

How is Coccidioides distinguished from all other dimorphic fungi?

A

It is a spherule in tissue (37°C), not a yeast

39
Q

What populations are at high risk for oral/esophageal thrush?

A

Immunocompromised: neonates, patients with diabetes and AIDS, chronic steroid users

40
Q

A 40-year-old immunocompromised man presents with pneumonia and verrucous skin lesions shortly after traveling to Wisconsin. What is the most likely diagnosis?

A

Blastomycosis

41
Q

How do you treat local infections of systemic mycoses?

A

With azoles (eg, itraconazole, fluconazole)

42
Q

What opportunistic fungus is a cause of endocarditis in IV drug users?

A

Candida albicans

43
Q

What part of the body is affected in a tinea unguium infection?

A

Nails (fungal nail infection is also termed onychomycosis)

44
Q

How do Mucor and Rhizopus spp. appear on culture media?

A

Broad, irregular, nonseptate hyphae that branch at wide angles

45
Q

What are the various prophylaxis options for Pneumocystis pneumonia?

A

Trimethoprim-sulfamethoxazole (TMP-SMX), dapsone, pentamidine, or atovaquone

46
Q

How does Pneumocystis pneumonia appear on methanamine-stained samples?

A

Disc-shaped yeasts

47
Q

Where is paracoccidioidomycosis endemic?

A

Latin America (Paracoccidioparasails with the captain’s wheel all the way to Latin America)

48
Q

You culture Cryptococcus neoformans at 25°C and then at 37°C. What morphology do you note?

A

C neoformans grows as a yeast at both temperatures (it is not dimorphic)

49
Q

What are the 3 different manifestations of tinea pedis?

A

Moccasin distribution, vesicular type, and interdigital (most common)

50
Q

Where is histoplasmosis endemic?

A

The Ohio and Mississippi River valleys

51
Q

What is the most specific test to confirm an infection with Cryptococcus neoformans?

A

Latex agglutination test to detect the polysaccharide capsular antigen

52
Q

A male patient, positive for HIV, has an infection with a heavily encapsulated, nondimorphic yeast. What stains are used to confirm the diagnosis?

A

India ink stain and mucicarmine; this is a Cryptococcus infection

53
Q

What is the appearance of Pneumocystis pneumonia on chest imaging?

A

Diffuse, bilateral ground-glass opacities with pneumatoceles

54
Q

What physical exam findings are evident in coccidioidomycosis?

A

Erythema nodosum (desert bumps) and multiforme arthralgias (desert rheumatism), may see meningeal signs if meningitis is present

55
Q

Where are the abscesses in Mucor and Rhizopus infections most commonly found?

A

Rhinocerebral and frontal lobes

56
Q

What do histoplasmosis, paracoccidioidomycosis, and blastomycosis have in common?

A

All are systemic mycoses caused by dimorphic fungi (metamorphosing into mold in cold [20°C] and into yeast in heat [37°C])

57
Q

Branching hyphae with rosettes of conidia grow on Sabouraud agar. How does this fungus appear when grown at 37°C?

A

Cigar-shaped buds (yeast phase); Sporothrix schenckii is dimorphic

NBME Micro (36 decks)

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