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PMI02-2010 Flashcards

1
Q

Are fungi eukaryotic or prokaryotic?

A

Eukaryotic

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2
Q

What are the two main types of fungi?

A

Yeast

Mould

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3
Q

Contrast yeast and mould.

A

Yeast = unicellular, reproduce by budding, some produce hyphae and pseudohyphae

Mould = multicellular, reproduce using specialised spore structures, always produce hyphae

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4
Q

Which type of fungi always produces hyphae?

A

Mould

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5
Q

Which type of fungi is unicellular and how does it reproduce?

A

Yeast

Reproduce by budding (making copies of itself)

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6
Q

What is budding?

A

Small cell forms off yeast cell and enlarges until its a complete cope

Separates and process repeats

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7
Q

Describe the growth of pseudohyphae.

A

Bud elongation

At max length, it buds again and elongates

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8
Q

What food do pseudohyphae resemble?

A

String of sausages

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9
Q

Describe true hyphae.

A

Produced by apical extension

Even and parallel sides which may have buds on its sides

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10
Q

What kind of appearance is produced by most yeasts?

A

Moist-looking colonies

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11
Q

Describe mould colonies.

A

Round (looking for nutrition in all directions)

Sub-surface growth occurs - hyphae above and below surface

Specialised spore structures on surface (to be distributed by air or water)

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12
Q

How could you tell the difference between a mould or yeast infection in skin using microscopy?

A

Mould = parallel-sided, regularly septate hyphae (true hyphae)

Yeast = budding yeasts, pseudohyphae and true hyphae

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13
Q

Name a species which is known to show budding, pseudohyphae and true hyphae.

A

Candida albicans

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14
Q

Name some commensal yeasts and where they’re typically found.

A

Candida albicans = GI tract and oral cavity

Other Candida species = GI tract

Malassezia species = skin

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15
Q

What does the presence of mould indicate?

A

Always infection (no commensal moulds)

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16
Q

Which yeasts cause candidiasis?

A

Candida species

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17
Q

List some factors that predispose for candidiasis.

A

Age - infancy and elderly due to immune function

Endocrine disorders (eg diabetes)

Defects in cell-mediated immunity

Cancer (impaired immunity)

Drug addiction - contaminated needles

Drug therapy - antibiotics, corticosteroids, immunosuppression

Surgery

Intravenous catheters - Candida biofilm

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18
Q

Are most Candida infections endogenous or exogenous?

A

Endogenous (found in GI tract)

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19
Q

Name some common Candida species in the body.

A

C. albicans

C. glabrata

C. tropicalis

C. parapsilosis

C. krusei

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20
Q

Which Candida species has some strains which are resistant to fluconazole?

A

C. glabrata

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21
Q

Which Candida species is completely resistant to fluconazole?

A

C. krusei

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22
Q

What is the most common type of exogenous Candida infection?

A

Nosocomial (in hospital)

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23
Q

Which Candida species is the most common culprit for hospital outbreaks?

A

C. albicans

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24
Q

Why is Candida auris a recent nosocomial issue?

A

Colonises people very quickly

Persistent in environment

Highly resistant to many antifungals

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25
What are some oral manifestations of candidiasis?
Acute pseudomembranous candidiasis (detachable plaques) Chronic pseudomembranous candidiasis - AIDS associated Chronic mucocutaneous candidiasis Angular cheilitis
26
What is chronic pseudomembranous candidiasis associated with?
AIDS
27
Describe chronic mucocutaneous candidiasis.
Presents in infancy/childhood and is usually inherited Associated with hypothyroidism or hypoparathyroidism or hypoadrenalism or idiopathic Recurrent oral, skin and nail infections Skin lesions crusted on face and scalp = "Candida granuloma" Immunological abnormality involved
28
Describe angular cheilitis.
4-8% of infants HIV+ = much increased risk Affects corners of mouth, across lips and tongue
29
How does Candida infection affect interdigital regions?
Moist, wet, sore
30
What causes onychomycosis and paronychia and how do they present?
Candida Discolouration and swollen and red bed of nails
31
Describe intertrigo.
Candida infection Submammary region Red, scaly with satellite lesions
32
What are risk factors for Candida infection?
Occlusion of skin (fingerwebs, finger nails, obesity) Wetness in folds Diabetes
33
Describe nappy dermatitis.
Affects buttocks, perianal and groin regions (nappy rash) Erythema, scaling and satellite lesions Candida may be a primary or secondary invader (damage due to urine and faecal matter)
34
What are some disposing factors to systemic candidiasis?
Age Immune state or suppression Antibiotics Abdominal surgery Catheters Prolonged hospitalisation
35
What areas are affected in systemic candidiasis?
Blood Lungs Internal organs Skin
36
List the virulence factors/mechanisms of Candida albicans.
Able to adapt to changes in environment Able to adhere to different surfaces Produces destructive enzymes (aspartyl proteinases, phospholipases, hyaluronidase) Can change cellular morphology to avoid recognition Produce biofilm structures as protection Evade host defence (kill monocytes, block degranulation) Produce toxins (candidalysin)
37
What surfaces/molecules is Candida albicans able to adhere to?
Has surface molecules that bind to iC3b, fibrinogen, laminin, epithelial cells Can aggregate with Streptococci and Fusobacterium
38
Describe the destructive enzymes produced by Candida albicans.
Secreted aspartyl proteinases, phospholipases, hyaluronidase Degrade ECM proteins to get nutrition and enable invasion Secreted aspartyl proteinases (SAP) have roles in adherence, invasion and development of disease
39
What are the functions of the different secreted aspartyl proteinases in Candida albicans infection?
1, 2, 3 = active during adhesion and are critical for mucosal infection 1 = skin penetration 4, 5, 6 = active in systemic infection
40
How can Candida albicans evade host defence mechanisms?
Block ROS production and degranulation of PMNs Kill monocytes Immunomodulatory effects of cell wall components cause cytokine release and complement activation
41
What is the toxin produced by Candida albicans and what does it do?
Candidalysin Cytolytic peptide secreted during hyphal invasion which damages tissues and activates the immune response
42
Describe cryptococcosis.
Chronic Subacute to acute pulmonary infection resulting from inhalation of Cryptococcus yeasts On dissemination, shows predilection for CNS --> cryptococcal meningtitis
43
What is Cryptococcus neoformans associated with?
Large amounts of bird droppings
44
Which patients are at major risk of cryptococcosis?
HIV/AIDs
45
Which Cryptococcal yeast is associated with large amounts of bird droppings?
Cryptococcus neoformans
46
Which Cryptococcal yeast is more likely to infect healthy people and what is it associated with?
Cryptococcus gattii Trees and soil
47
In what form does Cryptococcus grow?
Yeast form only - no hyphae
48
What is the major virulence factor of Cryptococcus?
Capsule - protective against drugs and prevents phagocytosis
49
Are mould infections endogenous or exogenous?
Exogenous
50
What are some predisposing factors to mould infections?
History of trauma to the site Host immune status - affects extent, duration and outcome of systemic infection Underlying disease Exposure to souce Portal of entry
51
What kind of infections do dermatophytes cause?
Tinea (superficial infections) - "ringworm fungi"
52
Who can be affected by dermatophytes and how is it spread?
Infects healthy and immunocompromised people Spread between people, animals and soil
53
What organism causes tinea?
Dermatophyte (mould)
54
Why do dermatophytes affect hair, skin and nails?
Uses keratin as a substrate
55
What is the commonest cause of skin and nail mould infections?
Trichophyton rubrum
56
What is the commonest cause of hair/scalp mould infection?
Trichophyton tonsurans
57
Describe tinea capitis.
Highly contagious scalp infection of children, often a bacterial infection too Highest incidence before puberty as sebum production inhibits fungal growth Minor trauma required to inoculate (scratching, sharing hats) More severe in immunocompromised than healthy but equal incidence Scaling, hair loss/patchy alopecia, mild erythema Lymphadenopathy at back of neck, kerion
58
What is a kerion?
Painful inflammatory mass where the body is fighting infection
59
Considering tinea capitis, why do we clean the headrest/chairs between patients?
Endothrix hair infection - spores within hair shaft and breakage will release them Clean to prevent spread to other patients
60
What pathogenicity mechanisms do dermatophytes have?
Adherence with adhesins, enzymes and fibrillar projections on cell surface Invasion with phospholipases, subtilisins, MMPs, carboxy proteinases Use a sulphite pump to reduce disulphide bonds in keratin to allow cleavage and access Immunomodulatory effect via cell wall mannans which suppress lymphoproliferative activity Different enzymes produced by fungi when attacking different hosts
61
What are the two main types of mould?
Dermatophytes Aspergillus
62
Describe Aspergillus.
Common in environment (ubiquitous) but uncommon infections Often infects immunocompromised hosts and cause systemic infection Involved in decay of leaves (compost), highest during autumn Disease type determined by host status
63
Name some of the commonest Aspergillus species.
A. fumigatus A. flavus A. nidulans A. niger A. terreus
64
Why are Aspergillus species referred to as a "species complexes"?
Each species comprises of closely-related organisms that can only be distinguished genetically
65
What is allergic aspergillosis?
Temporary presence of Aspergillus in respiratory tract in healthy hosts Mainly affects agricultural and horticultural workers
66
What is aspergilloma?
Inhalation of Aspergillus and colonisation of pre-existing cavities in lungs and form a fungal ball Predisposed by anything that causes lung cavitation but otherwise healthy hosts
67
Describe invasive aspergillosis.
Caused by A. fumigatus Has a pulmonary focus but can disseminate Linked to immunocompromised hosts
68
What is systemic aspergillosis?
When invasive aspergillosis leaves lungs and spreads to other organs, brain Only immunocompromised hosts
69
What may cause cutaneous aspergillosis?
Primary infection from skin damage and entry Secondary infection due to dissemination/systemic aspergillosis by travelling via blood Usually A. fumigatus or A. flavus
70
How is A. flavus often linked to food (eg peanuts)?
In contaminated food (peanuts usually), produces aflatoxin Causes aflatoxicosis when ingested so affects all hosts Liver damage and death
71
Which Aspergillus species is most common?
A. fumigatus

BDS2 PMI (21 decks)

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