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intruduction to fungi Flashcards

1
Q

fungi are eukaryotic or prokaryotic?

A

eukaryotic
• ‘eukaryotic,’ therefore true nuclei, internal organelles
• Not susceptible to antibiotics

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2
Q

describe the cell membrane of fungi

A

1) ontains ergosterol; analogous to cholesterol in humans
2) Phospholipid bilayer
3) Surrounds cytoplasm

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3
Q

what is the composition of fungal cell walls?

A

• Chitin + carbohydrates (ß-d-glucan and mannans)
• The chitin cell wall gives rigidity
• Antigenic
In contrast to the cell wall in plant cells, it does not contain cellulose.

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4
Q

what is the role of the chitin in the cell walls of fungi?

A

gives rigidity

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5
Q

do fungi have capsule?

A
  • Some fungi
  • Polysaccharide
  • Antiphagocytic virulence factor
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6
Q

what are the four basic morphological elements of fungi?

A
  • -particularly in dermatophytes and molds:
    1) Hyphae → multicellular compartments, which are connected by porous septa
    2) Mycelium → network of hyphae, which are formed by asexual reproduction
  • -Particularly in yeasts:
    1) Budding cells (blastospores) → in unicellular fungi, formed by budding off daughter cells
    2) Pseudomycelium → chains of budding cells, which are stretched in a hyphen-like manner, but are divided by septa
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7
Q

what is the clinical significance of ergosterol in cell membrane of fungi?

A

Azoles target the synthesis of ergosterol, the principal sterol in fungal cell membranes. They inhibit the synthesis of ergosterol from lanosterol by interfering with 14α-demethylase (cytochrome P-450 enzyme).

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8
Q

list a few substances that are synthesized by fungi?

A

1) Penicillin by Penicillium chrysogenum
2) Toxins:
- -Aflatoxins by molds (e.g., Aspergillus flavus) on nuts, seeds, and grains: poisonous carcinogen associated with hepatocellular carcinoma
- -Amanitin
- -Ergot alkaloids such as ergotamine produced by the ergot fungus Claviceps purpurea, which grows on rye: causes vasoconstriction by binding to 5-HT1D serotonin receptors and alpha-adrenergic receptors

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9
Q

what is the characteristic feature of yeasts?

A

Although yeast is single-celled organisms, they possess a cellular organization similar to that of higher organisms, including humans. Specifically, their genetic content is contained within a nucleus. This classifies them as eukaryotic organisms

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10
Q

how yeasts are reproduced?

A

by budding

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11
Q

describe the colonies of yeasts?

A

Moist, mucoid or waxy colonies

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12
Q

name few clinically significant yeasts

A

Cryptococcus neoformans

Saccharomyces cerevisiae

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13
Q

describe yeast-like fungi

A
  • Grow partly as yeast and partly as elongated cells resembling hyphae (pseudohyphae)
  • Reproduce by budding
  • Generally creamy white colonies
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14
Q

give example of yeast-like fungi

A

Candida

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15
Q

what are the molds?

A

is a fungus that grows in the form of multicellular filaments called hyphae. In contrast, fungi that can adopt a single-celled growth habit are called yeasts.

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16
Q

describe the characteristics of molds

A
  • Multicellular
  • Made up of clumps of intertwined branching hyphae
  • Grow by longitudinal extension
  • Produce spores
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17
Q

what is the hypha?

A

–is a long, branching filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth and are collectively called a mycelium.
• Tubules made up of fungal cells attached end to end
• Growth = extend in length from the tip of tubules

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18
Q

what is the mycelium?

A

a network of hyphae, which are formed by asexual reproduction

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19
Q

what are the reproducing bodies of molds?

A
  • Spores

* The reproducing bodies of molds

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20
Q

what are the dimorphic fungi?

A

A fungus that has both a hyphal (mold) form at colder temperatures and a yeast or spherule form at warmer temperatures. Examples include Blastomyces dermatitidis, Candida albicans, Histoplasma capsulatum, Sporothrix schenckii, Blastomyces dermatitidis, and Coccidioides immitis.
• Molds in environment at 25-30° C
• Yeasts in human tissues at 35-37° C

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21
Q

what are the filamentous fungi?

A
  • -Dermatophytes

- -Aspergillus

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22
Q

what patients are vulnerable to fungal infections?

A

– Chemotherapy
– Transplantation
– Immunomodulatory therapies

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23
Q

give examples of superficial vs subcutaneous vs systemic fungal infections

A 
•	Superficial
	e.g. Dermatophytosis, thrush
•	Subcutaneous
	e.g. Sporotrichosis
•	Systemic
	e.g. Cryptococcal meningitis
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24
Q

hypersensitivity is seen with what fungi?

A

Aspergillus - induced asthma
Broncho-pulmonary aspergillosis
(actually, granulomas seen with some fungi are a result of type 4 hypersensitivity reaction)

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25
Q

how fungi cause disease?

A

1) invasion
2) hypersensitivity
3) toxins

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26
Q

give examples of superficial skin infections

A

Limited to outermost layers of skin, hair, nails and mucosa
1. Pityriasis Versicolor (pigmented lesions on the upper torso)
2. Dermatophytosis (Ringworm/tinea)
3. Candidiasis
Diagnosis – skin scrapings (KOH - microscopy)

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27
Q

how superficial fungal infections are diagnosed?

A

skin scrapings (KOH - microscopy)

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28
Q

what is pityriasis Versicolor?

A

A benign, superficial skin infection most commonly caused by the yeast species Malassezia furfur and Malassezia globosa. Particularly common in warm, humid climates and in individuals with hyperhidrosis. Presents with mildly pruritic, clearly demarcated macules with a fine-scale that become noticeably hypopigmented after exposure to the sun.

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29
Q

what is caused by Malassezia furfur?

A

Pityriasis Versicolor

a. Common – patchy rash
b. Pale brown/pink macules - Pale patches more common in darker skin c.
c. Itchy
d. Trunk / Neck most common

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30
Q

what is the Woods lamp examination?

A

a diagnostic test to examine skin lesions with a lamp that emits ultraviolet light. Used to evaluate hypopigmented or depigmented lesions (e.g., vitiligo) and superficial fungal infections of the skin (e.g., erythrasma), which appear characteristically fluorescent under ultraviolet light.

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31
Q

how pityriasis versicolor is diagnosed?

A

diagnostic test to examine skin lesions with a lamp that emits ultraviolet light. Used to evaluate hypopigmented or depigmented lesions (e.g., vitiligo) and superficial fungal infections of the skin (e.g., erythrasma), which appear characteristically fluorescent under ultraviolet light.

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32
Q

what is the characteristic pattern of pityriasis versicolor seen on skin scrapings?

A

potassium hydroxide (KOH) preparation of skin scrapings demonstrates the “spaghetti and meatballs” pattern

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33
Q

how pityriasis versicolor is treated?

A 
•	Topical: 
–azoles (ketoconazole)
–Selenium sulfide
•	Oral azoles:
–Fluconazole
–Itraconazole
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34
Q

what is the tinea?

A

A group of fungal skin infections often caused by dermatophytes. It can affect a variety of areas of the body, including: feet (tinea pedis), nails (tinea unguium), scalp (tinea capitis), torso (tinea corporis) and groin (tinea cruris). Less commonly-affected areas include the face (tinea faciei), hands (tinea manuum), and beard (tinea barbae).

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35
Q

what is the ringworm?

A

A dermatophyte infection that affects a body area other than the feet, scalp, nails, or groin. Manifests with erythematous, round, pruritic plaques with central clearing and raised borders (ringworm appearance).

36
Q

what genera of dermatophytes do you know?

A

o Trichophyton spp
o Epidermophyton spp
o Microsporum spp
-affect keratinized tissue

37
Q

how does KOH test work?

A

A quick, inexpensive test to differentiate certain fungal infections (e.g., dermatophytes, Candida) from other skin disorders (e.g., eczema, psoriasis). A sample of the affected area is evaluated under a microscope after the addition of potassium hydroxide (KOH). KOH is a strong alkali that dissolves cells and protein debris in specimens but leaves fungal elements (e.g., budding yeasts, hyphae, spores, and pseudohyphae).

38
Q

what agar is used to grow fungi?

A

Sabouraud agar

A growth medium that contains dextrose and peptones. Used to culture dermatophytes and other fungi.

39
Q

how tinea are treated?

A
  • Oral terbinafine

* Topical antifungals (terbinafine, clotrimazole) and keratolytic agents

40
Q

how does terbinafine work?

A

inhibit fungal squalene epoxidase, which decreases ergosterol synthesis
Adverse effects include taste disturbance, gastrointestinal upset, hepatotoxicity, and headaches.

41
Q

give an important example of subcutaneous mycosis

A

• Involves deeper layers of the dermis and subcutaneous tissue
•At sites of trauma – acquired from soil/thorns
– Sporotrichosis – Sporothrix schenckii (dimorphic fungus)

42
Q

what are the clinical features of sporotrichosis?

A

Manifestations include localized skin lesions (e.g., pustules, ulcers, nodules) and ascending lymphangitis. It can become disseminated in patients who are immunocompromised.
Gardeners are at risk

43
Q

how sporotrichosis is treated?

A
  • Itraconazole

* Pulmonary or Disseminated disease = Amphotericin B

44
Q

how amphotericin B works?

A

Bind to ergosterol in the fungal cell membrane forms pores that disrupt electrolyte balance

45
Q

describe cryptococcus neoformans?

A

– Yeast (encapsulated)
– Soil, avian faeces, rotting vegetation
– Inhaled into lungs – generally no symptoms
– Meningitis in immunosuppressed patients

HIV
– Organ transplant
– Steroids
– Malignancy

46
Q

how cryptococcal infection is diagnosed?

A
  • Clinical suspicion
  • Antigen detection in blood & CSF
  • Microscopy (India-ink) rarely used now
  • Culture of CSF, blood
  • 18s PCR on tissue samples
47
Q

what are the features of Histoplasma capsulatum?

A

• Grow as molds at 25°C, yeasts at 37°C
• Not common in Ireland, UK or rest of Europe but found in North America
• Found in soil
• Guano from birds & bats
• Caves!
• May cause (clinically)
1)Asymptomatic infection
2)Acute/ chronic respiratory infection resembling TB
3)Disseminated, involving liver, lungs, spleen (immunosuppressed patients)
• Fungus lives intracellular in macrophages => immune-evasion

48
Q

what are the risk factors of Histoplasmosis

A

caving

49
Q

in what cells Histoplasma lives?

A

in macrophages

50
Q

what animal is a risk factor of Hisoplasmainfection?

A

bats

51
Q

what is the paracoccidioides?

A

A dimorphic fungus endemic to Latin America that causes paracoccidioidomycosis if its spores are inhaled. Forms large, budding yeast with a characteristic shape that resembles a captain’s wheel.
Cause skin and mucosal ulcers, granulomas

52
Q

what are the manifestations of paracoccidioides?

A
  • -Acute pneumonia
  • -Painful nasal, pharyngeal, and laryngeal mucosal ulcerations
  • -Lymphadenopathy (usually cervical)
  • -Can disseminate → extrapulmonary manifestations (including verrucous skin lesions)
53
Q

what are the features of candida species?

A
  • Pseudo-yeasts, eg Candida albicans, C. tropicalis, etc
  • Part of the normal flora of mouth, intestine and lower genital tract
  • Opportunist pathogens, of increasing importance
  • Superficial & systemic infections
54
Q

what skin lesions cause candida species?

A
  • Erythema, plaque-like lesions
  • Warm, moist areas, skin folds (axilla, groin, perineum, under breasts) - intertrigo
  • Itchy, red, macular rash
55
Q

what is the intertrigo?

A

n inflammation if the skin that particularly affects skin folds (submammary, inguinal, interdigital). Typically manifests as white macerations on an erythematous base with satellite lesions and possibly scaling. Most commonly caused by infection with candida albicans. Aggravating factors include obesity, sweat, feces, urine, and vaginal discharge.

56
Q

what are the risk factors of candida infection?

A
  • Antibiotics
  • Steroids
  • Pregnancy
  • Immunosuppression
57
Q

candida vaginal is more aftermenopause

True/False

A

False

As there is a hypoestrogenic state

58
Q

how candida skin infections are treated?

A

– Topical antifungal agents: Clotrimazole

– Oral: Fluconazole

59
Q

what is the oral thrush?

A

localized, mucocutaneous Candida infection characterized by white plaques in the oral cavity that can be scraped off, giving way to red, inflamed, or bleeding areas. Other manifestations include a cottony feeling in the mouth, loss of taste, and in some cases, pain while eating.
Thrush can be also 1)Oral 2)Vaginal 3)esophageal (esp. HIV)

60
Q

what are the risk factors of invasive Candidal infection?

A 
–	Antibiotic or steroid therapy
–	Immunosuppressed (HIV, chemo)
–	Transplant (SOT and BMT)
–	Post-operative – GI surgery
–	Intravenous catheters/indwelling devices
–	Diabetes mellitus/Burns
–	ICU
–	PN (parenteral nutrition)
61
Q

what is the most common risk factors for systemic candidiasis?

A

– The major disease of immunocompromised hosts

– The fourth commonest cause of bloodstream infection in hospital patients

62
Q

how invasive candidiasis is diagnosed?

A 
–•	Specimens: 
–	Blood, sterile site samples, tissue
•	Microscopy :
–	Budding yeasts
–	Gram-positive- large dark purple cells
–	Germ tube test
•	Culture:
–	Grow aerobically on blood and selective agar (Sabouraud dextrose agar, Chromogenic agar)
•	Identification
- MALDI-TOF
63
Q

what is the germ tube?

A

A germ tube is an outgrowth produced by spores of spore-releasing fungi during germination.

  • -Candida spp. form yeast cells and pseudohyphae at 20–25°C
  • -Candida albicans forms germ tubes at 37°C
64
Q

what is MALDI-TOF

A

Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI TOF-MS) allows rapid and accurate identification of microorganisms.

65
Q

candida is G+ or G-

A

albicans can take on either a unicellular (yeast) or multicellular (hyphae, pseudohyphae) form. The yeast form is 10-12 microns across and is Gram-positive.

66
Q

what are the features aspergillus

A

• Mold/ filamentous fungus
• Found in soil, air, plants and decomposing organic matter
• Hospital environments: construction work
• Spore-forming organism
–Spores inhaled
–Germinate to form hyphae
–Destruct blood vessels & disseminate
• Allergy due to the reaction to Aspergillus antigens in atopic individuals

67
Q

what are the clinical features of aspergillosis?

A
  1. Allergic aspergillosis
    - Sinusitis
    - Broncho pulmonary
  2. Allergic bronchopulmonary aspergillosis (ABPA)
  3. Aspergilloma
  4. Invasive aspergillosis
68
Q

what is the ABPA?

A

Chronic exposure to Aspergillus can result in ABPA, presenting with asthmatic symptoms or sinusitis, especially in patients with a history of asthma or cystic fibrosis. It is primarily managed with glucocorticoid therapy.

69
Q

ABPA present with eosinophilia. True/False

A

True

• Eosinophilia, high IgE

70
Q

how ABPA is diagnosed?

A
  • Diagnosis –high antibody titers in serum

* Fleeting CXR changes

71
Q

what are the clinical features of BAPA

A
  • Bronchospasm, obstruction
  • Wheeze, cough, SOB, fever
  • Treat with steroids +/- itraconazole
72
Q

what is the aspergilloma?

A

A fungal mass in a pre-existing cavity that mainly affects the lungs and is visible on a chest X-ray as a “fungus ball” that moves on the repositioning of the patient. It is a form of chronic pulmonary aspergillosis.
– Sputum positive in 66%
– Antibodies positive in 70%

73
Q

what are the clinical features of aspergilloma?

A

Asymptomatic, chronic cough, hemoptysis

74
Q

how aspergilloma is treated?

A

surgery

75
Q

what are the risk factors of invasive aspergillosis?

A 
–	Prolonged neutropenia (> 14 days) e.g. AML
–	Transplantation 
–	HIV
–	Diabetes mellitus
–	High dose steroids
–	Major surgery
76
Q

what is the pathophysiology of invasive aspergillosis?

A

– The primary site is lung
– Macrophages/Neutrophils eradicate inhaled spores in immunocompetent
– Widespread destructive growth in lung tissue
– Invasion of blood vessels
– Dissemination to other sites(liver, spleen, kidney, CNS)
– Poor prognosis

77
Q

the primary site of infection leading to invasive aspergillosis?

A

The primary site is the lung

78
Q

what serum test is used to diagnose aspergillosis

A

galactomannan test: Galactomannan antigen is a heteropolysaccharide component of the Aspergillus cell wall that is shed during the phase of hyphal growth.

79
Q

what is the difference between the galactomannan and 3-β-D glucan test?

A

,3-β-D glucan tests are nearly as sensitive as galactomannan antigen assays but have a low specificity because they can also be seen with invasive candidiasis.

80
Q

what are the risk factors for pneumocystis jiroveci infection?

A

• Opportunistic lung infection in immunosuppressed patients
– HIV
– Organ transplantation especially lung
– Haematopoetic stem cell transplant
– Corticosteroid treatment
• Incidence has greatly declined since the introduction of prophylaxis

81
Q

what stain is used to diagnose P. jiroveci?

A

Methenamine silver
A yeast-like fungus originally classified as a protozoan that causes Pneumocystis pneumonia. Identified as disc-shaped yeast form on methenamine silver stain of lung tissue.

82
Q

what are the clinical feature of pneumocystis jiroveci infection

A

Symptoms typically have a gradual onset (days to weeks) and include:
-Low-grade fever and malaise
-Dyspnea and non-productive cough
-Fatigue, weight loss, chills
May progress to fulminant respiratory failure
Can be asymptomatic

83
Q

how pneumocystis is diagnosed?

A

If PCP is suspected based on the history and clinical examination, oxygen saturation, the CD4+ count, the beta-D-glucan level should be measured and a CXR conducted. If the CXR is inconclusive, a high-resolution CT scan can be obtained. The diagnosis should generally be confirmed via microscopic identification of P. jirovecii from respiratory secretions.

84
Q

what are the CXR and CT abnormalities of Pneumocystis pneumonia?

A

1) Chest X‑ray
- -Typically symmetrical, diffuse interstitial infiltrates extending from the perihilar region, ground glass infiltrates
- -May sometimes be normal
2) High-resolution CT
- -Indicated if PCP is still suspected in a patient with a normal CXR
- -High sensitivity for PCP; a negative scan thus suggests the diagnosis of PCP is unlikely

85
Q

what is the confirmatory test for PCP?

A

microscopic identification of P. jirovecii in a specimen obtained via bronchoalveolar lavage or induced sputum, with methenamine silver staining and immunofluorescence
Staining enables visualization of disc-shaped P. jirovecii cysts with central spores
these cysts resemble “crushed ping-pong balls” with central “dots”.

micro_db (18 decks)

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