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Clinical Microbiology > Yeasts > Flashcards

Yeasts Flashcards

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1
Q

Yeasts

A

Eukaryotic, unicellular organisms. They are oval, elongate, or irregular shaped. They multiple by producing Blastoconidia – budding, pseudohyphae. Colonies are moist, creamy, and glabrous. They may produce a capsule (mucoid) or may be darkly pigmented (melanin production). Inhibited by cyclohexamide

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2
Q

How are yeasts identified?

A

Macro and microscopic methods- corn meal, rapid biochemical testing, and molecular methods in development

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3
Q

Yeasts as normal flora

A

Yeast are normal microbiota and common contaminants. Interpretation of a significant isolate difficult from site where usually considered normal microbiota- sputum and stool vs sterile body sites (blood, CSF, etc.)

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4
Q

Considerations for patients with yeast infections

A

Need to consider the quantity of yeast vs. bacteria (normally less than bacteria). Also, if the patient is on antimicrobial treatment, this could increase yeast. Not reporting Genus and species may lead to consequences-Candida tropicalis can be aggressive in immunocompromised people.
Isolation from sterile body sites is always considered a significant isolate.

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5
Q

Specimen collection and transport

A

Special transport is not needed, but it should be less than 2 hours. If there is a delay for sterile body site specimens place at 37°C. If there is a delay for specimen containing normal flora bacteria, the recommendation is 4°C. Yeast can withstand refrigeration

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6
Q

Special plating considerations (2)

A

There are special considerations if ruling out:
1. Coccidiodes immitis – highly infectious
2. Malassezia furfur – lipid growth requirement

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7
Q

Microscopic identification of direct yeast specimens (5)

A
  1. Gram stain of specimen-budding yeast, pseudohyphae OR true hyphae
  2. Wet prep – patient sample and saline for review
  3. 0-40% KOH
  4. Calcofluor white stain
  5. India Ink – capsule visualization
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8
Q

Growth characteristics of yeast

A

Most grow well on both yeast/fungus and bacteria specific media, but Malassezia sp. is an exception. 48 to 72 hours is necessary for good colony growth. Temperature-
30 or 37°C. Yeast form smooth, creamy colonies. Morphology-pigment, “Feet”, Mucoid – capsule

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9
Q

Sabouraud dextrose agar

A

Mycology specific media lacking cyclohexamide- primary plated media

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10
Q

Germ tube

A

Hyphal-like extension of yeast cells that are not constricted. Yeasts are incubated with serum at 37oC for up to 3 hours and examined microscopically. Candida albicans, tropicalis =(>2hrs), dubliniensis (not in commercial media). Rapid and inexpensive test, incubation of less than 3hr is a false positive

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11
Q

Rapid Systems

A

Use carbohydrate or nitrate assimilation for full identification. Identification systems include Vitek-Yeast Biochemical Card, Microscan Rapid Yeast ID and API 20C, API Candida, Uni-Yeast Tek. Also includes Cornmeal Tween 80

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12
Q

Assimilation

A

Utilization of carbon or nitrogen source by a microorganism in the presence of oxygen

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13
Q

Biochemical identification of yeast (9)

A
  1. Germ tube
  2. Rapid systems- MALDI-TOF, PCR
  3. Chromogenic agars - CHROMagar Candida
  4. Phenol oxidase test
  5. Urease test
  6. PNA-FISH
  7. Molecular methods
  8. Rapid nitrate assimilation
  9. Rapid trehalose
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14
Q

Cornmeal Tween 80

A

basic media utilized to cultivate the growth of many fungal isolates while also inhibiting the growth of contaminating bacterial flora and some saprophytic fungi. Identification is confirmed with morphology. Chlamydospore development and Blastoconidia, arthroconidia, pseudohyphae and true hyphae. Used for Candida Albicans.

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15
Q

Nitrate assimilation is used for which species? (3)

A

Best for ID of Candida, Cryptococcus or Rhodotorula spp.

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16
Q

Chromogenic agars

A

Includes CHROMagar Candida. Differentiation of 10 species, presumptive ID of C. albicans, C. tropicalis, C. krusei. Identifications are only presumptive, variation in colony color is found

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17
Q

Phenol oxidase test

A

Detects ability of Cryptococcus neoformans to produce phenol oxidase on substrates containing caffeic acid. Uses bird seed agar - niger or thistle seed. Dark brown to black growth - Cryptococcus neoformans

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18
Q

Urease test

A

Test for urease using a urea slant, takes 24 to 72 hours. Turning a pink color is a positive result. ID for Cryptococcus sp., Rhodotorula sp., Trichosporon sp.

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19
Q

PNA-FISH

A

Full identification in 2.5 hours- commercial peptide nucleic acid fluorescent in situ hybridization. Identification of C. albicans from blood cultures only using 26S rRNA. Peptide-nucleic acid chains mimic rRNA, hybridize to target rRNA

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20
Q

Molecular methods (3)

A
  1. T2 Biosystem
  2. NAAT
  3. BioFire for blood culture
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21
Q

Rapid nitrate assimilation

A

Use of KNO3 as a sole source of nitrogen- reduction of nitrate to nitrite. Differentiate between Cryptococcus spp. isolates and Rhodotorula

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22
Q

Rapid trehalose

A

Utilization of trehalose in the presence of a protein inhibitor. C. glabrata degrades trehalose quicker, producing increased acid as compared to other yeasts.

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23
Q

Commonly isolated pathogenic yeasts (7)

A
  1. Candida species
  2. Cryptococcus sp.
  3. Trichosporon sp.
  4. Malassezia sp.
  5. Rhodotorula sp
  6. Saccharomyces sp.
  7. Geotrichum sp.
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24
Q

Candida species (10)

A
  1. Albicans/dubliniensis
  2. Auris
  3. Tropicalis
  4. Glabrata complex
  5. Parapsilosis complex
  6. Pichia kudriavzevii
  7. Kluyveromyces marxianus
  8. Clavispora lusitaniae
  9. Meyerozyma guilliermondii
  10. Yarrowia lipolytica
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25
Q

Cryptococcus species (4)

A
  1. Neoformans
  2. Gattii
  3. Albidus
  4. Laurentii
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26
Q

Malassezia species (5)

A
  1. Furfur
  2. Globosa
  3. Sympodialis
  4. Obtusa
  5. Restricta
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27
Q

Which Candida species are most invasive? (5)

A

95% of all invasive Candida infections are caused by 5 species:
1. Albicans
2. Glabrata complex
3. Tropicalis
4. Parapsilosis
5. Pichia kudriavzevii (formerly Candida krusei)

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28
Q

Infections caused by Candida species (8)

A
  1. Oral candidiasis (thrush)
  2. Vaginal candidiasis
  3. Cutaneous candidiasis
  4. Onychomycosis
  5. Bronchopulmonary
  6. Urinary tract infection
  7. Intestinal candidiasis
  8. Systemic
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29
Q

Oral candidiasis (thrush) risk factors (9)

A

Risk factors- infants or elderly, immunosuppressed (AIDS), transplant recipients
leukemia, cancer, TB, diabetes
oral contraceptives, antibacterial treatment

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30
Q

Vaginal candidiasis risk factors

A

Pregnancy or diabetes. Needs to be isolated repeatedly

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31
Q

Cutaneous candidiasis

A

Red, inflamed patches that can be localized or disseminated. Yeast are isolated in large numbers. Risk factors- obese, alcoholic, profuse sweating

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32
Q

Onychomycosis

A

Candidiasis of nail

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33
Q

Bronchopulmonary candidiasis

A

A secondary infection following antimicrobial therapy. Symptoms- irritating cough, mucoid sputum. Pneumonia is visible on x-ray

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34
Q

Intestinal candidiasis

A

Follows antimicrobial therapy that suppresses normal flora. Stool culture has predominant yeast growth

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35
Q

Systemic candidiasis

A

Hematogenous spread of the fungus occurring in debilitated patients. Inoculation can occur by medical devices or break in the skin barrier. Complications of the infection include endocarditis, meningitis, brain abscess, sepsis. There is a 19-24% mortality rate

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36
Q

Candida albicans habitat

A

In is normal flora of the skin, mouth, vagina, and stool. It is also found in the environment in leaves, flowers, water, and soil

37
Q

Clinical significance of Candida albicans

A

Most common cause of mycoses worldwide. Grows at 42-45 degrees Celsius and is germ tube positive

38
Q

Macroscopic and microscopic features of Candida albicans

A

Macroscopic- colonies appear cream colored, pasty, smooth, colonies have feet. CHROMagar -light green to light bluish-green. Microscopic- single yeast, budding, pseudohyphae

39
Q

How do candida albicans appear on cornmeal?

A

Pseudohyphae, clusters of Blastoconidia, thick-walled terminal, single chlamydospores

40
Q

Clinical significance of candida glabrata

A

Cause bloodstream, urogenital, lung and other infections. Difficult to treat, resistant to azole, reduced susceptibility to Amphotericin B. Echinocandins can be used for treatment.

41
Q

How does candida glabrata appear on cornmeal?

A

There is only a small, single, oval budding yeast

41
Q

How does Candida glabrata appear macroscopically and microscopically?

A

Macroscopic- colonies are small, white to cream, pasty, and smooth
Microscopic- single budding yeast (condida), there are no pseudohyphae

42
Q

Clinical significance of Candida tropicalis

A

Found in immunocompromised people, similar to all other Candida species. It is problematic in leukemia patients and other cancer patients

43
Q

How does candida tropicalis appear macroscopically and microscopically?

A

Macroscopic- colonies are cream colored and the edges may be wrinkled. Appear metallic blue on CHROMagar.
Microscopic- round to oval yeast cells

44
Q

How does candida tropicalis appear on cornmeal?

A

Oval blastospores may appear singly or in clusters located along the long pseudohyphae. Pseudohyphae branch abundantly, rare true hyphae

45
Q

Clinical significance of candida dubliniensis

A

Found worldwide. It is frequently associated with HIV resulting infections and bloodstream infections in non-HIV immunocompromised patients. These fungi do not grow at 42-45 degrees Celsius and are germ tube positive

46
Q

How does candida dubliniensis appear macroscopically and microscopically?

A

Macroscopic- colonies are white to cream, soft, and can be smooth or wrinkled. On CHROMagar, they appear dark green
Microscopic- only blastoconidia

47
Q

How do candida dubliniensis appear on cornmeal?

A

Branched pseudohyphae & true hyphae with Blastoconidia are present. Abundant chlamydoconidia includes single, pairs, chains, and clusters.

48
Q

Candida auris habitat

A

Hospital and nursing home acquired. Found in many body sites and fluids, including blood, urine, respiratory and abdominal specimens

49
Q

Clinical significance of Candida auris

A

These infections are very serious, they can cause significant bloodstream or brain infections that may lead to death. They are difficult to identify on automated systems since they can’t be differentiated from other species- MALDI-TOF or DNA sequencing must be used for an accurate identification. Candida auris is germ tube negative and grows well at 40-42. It has multi-colored colonies on CHROMagar

50
Q

Candida auris treatment

A

Treatment is difficult since these fungi are resistant to many antifungals. Resistant to azoles, possible amphotericin B, 5FC, echinocandin resistance

51
Q

How does Candida auris appear macroscopically and microscopically?

A

Macroscopic- white to cream
Microscopic- Blastoconidia (budding yeast), almost never forms pseudohyphae

52
Q

Candida parapsilosis morphology

A

Radiating pseudohyphae and scattered blastoconidia, producing what are known as “spider” colonies

53
Q

Pichia kudriavzevii morphology

A

Formerly Candida krusei- long, wavy, branched pseudohyphae with elongated to ovoid Blastoconidia, budding off in branches.

54
Q

C. neoformans habitat

A

Pigeon roosts, fruit, milk, plants. Aerosolization and inhalation of pigeon excrement is thought to be the infection route

55
Q

C. gatti habitat

A

Tropical and subtropical regions. US/Canada (BC, Vancouver, Washington) – trees, soil, water, wood products. Caused by inhalation of spores from the environment

56
Q

Clinical significance of C. neoformans

A

Inhibited by cyclohexamide, affects the immunocompromised especially HIV(meningitis). Causes CNS infections, lesions on the skin, in the lungs, and other organs. Primarily a pulmonary disease. Latex agglutination for detection of cryptococcal antigen simple, sensitive and reliable - detects 90% of all cryptococcal meningitis cases.

57
Q

C. gattii clinical significance

A

Inhibited by cyclohexamide, recent pathogen, affects immunocompetent individuals. The primary site of infection is the lungs, where it causing pneumonia. Dissemination to other organs, notably the central nervous system (CNS), causes meningoencephalitis or brain cryptococcomas. Increasingly found in immunocompromising conditions.

58
Q

How do cryptococcus species (neoformans, gattii) appear macroscopically?

A

Both strains are identical. Colonies are cream then turn a tan color as they age. They are flat or heaped, mucoid and have smooth edges. Phenol oxidase positive, form brown to black colonies on bird seed or caffeic acid

59
Q

How do cryptococcus species (neoformans, gattii) appear microscopically?

A

The fungi are round, dark-walled, budding yeast. They produce capsules

60
Q

How do cryptococcus species (neoformans, gattii) appear on cornmeal?

A

Round, dark-walled budding yeast- no hyphae

61
Q

Saccharomyces sp habitat

A

Commonly isolated from humans, mammals, birds, wine, beer, fruits, trees, plants, olives, and soil. Common colonizer of mucosa surface, known as “baker’s” or “brewer’s” yeast

62
Q

Saccharomyces sp clinical significance

A

Non-pathogenic for immunocompetent, but RARE report of fungemia & aortic graft infection in immunocompetent.
Severe immunosuppression causes mucosal and disseminated disease-pneumonia, endocarditis, liver abscess, fungemia, and sepsis

63
Q

Saccharomyces sp macroscopic appearance

A

Rapid growth, mature in 3 days. Colonies - flat, smooth, moist, glistening or dull, cream to tannish color

64
Q

Saccharomyces sp microscopic and cornmeal appearance

A

Blastoconidia - unicellular, ellipsoid to elongate, multilateral budding is typical. Pseudohyphae, if present, are rudimentary, hyphae are absent

65
Q

Saccharomyces cerevisiae virulence factors

A

So far, none have been identified. In a case review of 3300 yeast infection of cancer patients, 19 were identified as S. cerevisiae. In another case review, of 138 systemic fungal infections over a 15 year period, only 2 identified as S. cerevisiae. It was found that strains recovered from infected immunocompromised hosts were more resistant to host oxidative stresses. Can cause mucosal and disseminated infection in significantly immunocompromised hosts.

66
Q

Malassezia sp habitat

A

Lipophilic yeast found on skin and body surfaces of humans and animals

67
Q

Malassezia sp clinical significance

A

Causes catheter-associated fungemia in neonates and adults receiving prolonged intravenous lipids. May also cause lung infections. Symptoms- tinea versicolor or pityriasis versicolor – multi-colored skin

68
Q

Malassezia sp macroscopic appearance

A

Smooth, cream to yellowish brown, with age – dry, wrinkled and brittle

69
Q

Malassezia sp microscopic appearance

A

These fungi do not bud. They form phialides with small collarettes. Thick round to oval yeast-like cells in clusters, spaghetti and meatballs morphology

70
Q

Malassezia sp appearance on cornmeal

A

Hyphal elements rare, phialides

71
Q

Malassezia sp virulence factors

A

Nutritional requirements leads to pathogenesis- the organisms are unable to synthesize medium and long chain fatty acids. Patients receiving central-line mediated total parenteral nutrition supplementation can be at increased risk of infection.
10% of newborns in non-NICU colonized. Additionally, 80% of newborns in the NICU are colonized. There is an increased association with prematurity, immunocompromised people, prolonged antimicrobial use and prolonged hospital stay. Infection causes fever, respiratory distress, sepsis, and it most commonly causes superficial skin infections

72
Q

Growth of M. furfur

A

M. furfur requires lipid supplementation for in vitro growth. Add olive oil to culture

73
Q

Rhodotorula sp habitat

A

Air, soil, lakes, ocean water, and dairy products. Colonizes plants, humans, other mammals

74
Q

Rhodotorula sp. clinical significance

A

Opportunistic mycoses in AIDS or acute leukemia patients - meningitis, endocarditis, ventriculitis, peritonitis, endophthalmitis, central venous catheter-infections, fungemia

75
Q

Rhodotorula sp. macroscopic appearance

A

Rapid grower, smooth, glistening, mucoid - cream to pink, coral red, orange or yellow colonies

76
Q

Rhodotorula sp. microscopic and corneal appearance

A

Blastoconidia- unicellular, elongate in shape, may be encapsulated. Pseudohyphae and hyphae are absent

77
Q

Geotrichum sp. habitat

A

Worldwide - soil, water, air, sewage, plants, cereals, and dairy products. They are normal human flora from sputum and feces, colonizer GI tract

78
Q

Geotrichum sp. clinical significance

A

Opportunistic infections (inhalation or ingestion) = geotrichosis. Causes bronchial, pulmonary, disseminated infections, and infections from trauma

79
Q

Geotrichum sp. macroscopic appearance

A

Rapidly growth, white, dry, powdery to cottony colony, resembling “ground glass.” When disturbed on the surface, the colony becomes yeast-like or slimy. The optimal growth 25°C, most strains = NG or weak growth at 37°C

80
Q

Geotrichum sp. microscopic appearance

A

Arthroconidia and coarse true hyphae are observed. Formation of arthroconidia and absence of empty cells that fragment to release arthroconidia (“disjunctor cells”) are typical. Blastoconidia, conidiophores, pseudohyphae = absent.

81
Q

Trichosporon sp. habitat

A

Found in soil, water samples, vegetables, mammals, and birds. They are normal flora of the mouth, skin and nails

82
Q

Trichosporon sp. clinical significance

A

White Piedra – forms white nodules on the hair shaft. Causes superficial and deep disseminated infections in humans. At risk populations include neutropenic patients and immunocompromised individuals

83
Q

Trichosporon sp. macroscopic appearance

A

Cream progresses to a yellow/gray color. Appears smooth at first, then wrinkled and powdery-like.

84
Q

Trichosporon sp. microscopic appearance

A

Oblong yeast cells

85
Q

Trichosporon sp. cornmeal appearance

A

True hyphae, pseudohyphae with Blastoconidia singly or in short chains. Arthroconidia on older cultures

86
Q

Chlamydospore

A

Chlamydospores are produced by many fungi and represent enlarged, thick-walled vegetative cells with varied forms and condensed cytoplasm

87
Q

Blastoconidia

A

A fungal cell produced by budding

88
Q

Arthroconidia

A

A spore that is formed from the hyphae by fragmentation. Microscopically, mature arthroconidia appear square, rectangular, or barrel-shaped with thick walls.

Clinical Microbiology (19 decks)

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