PMI02-2010 Flashcards
Are fungi eukaryotic or prokaryotic?
Eukaryotic
What are the two main types of fungi?
Yeast
Mould
Contrast yeast and mould.
Yeast = unicellular, reproduce by budding, some produce hyphae and pseudohyphae
Mould = multicellular, reproduce using specialised spore structures, always produce hyphae
Which type of fungi always produces hyphae?
Mould
Which type of fungi is unicellular and how does it reproduce?
Yeast
Reproduce by budding (making copies of itself)
What is budding?
Small cell forms off yeast cell and enlarges until its a complete cope
Separates and process repeats
Describe the growth of pseudohyphae.
Bud elongation
At max length, it buds again and elongates
What food do pseudohyphae resemble?
String of sausages
Describe true hyphae.
Produced by apical extension
Even and parallel sides which may have buds on its sides
What kind of appearance is produced by most yeasts?
Moist-looking colonies
Describe mould colonies.
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)
How could you tell the difference between a mould or yeast infection in skin using microscopy?
Mould = parallel-sided, regularly septate hyphae (true hyphae)
Yeast = budding yeasts, pseudohyphae and true hyphae
Name a species which is known to show budding, pseudohyphae and true hyphae.
Candida albicans
Name some commensal yeasts and where they’re typically found.
Candida albicans = GI tract and oral cavity
Other Candida species = GI tract
Malassezia species = skin
What does the presence of mould indicate?
Always infection (no commensal moulds)
Which yeasts cause candidiasis?
Candida species
List some factors that predispose for candidiasis.
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
Are most Candida infections endogenous or exogenous?
Endogenous (found in GI tract)
Name some common Candida species in the body.
C. albicans
C. glabrata
C. tropicalis
C. parapsilosis
C. krusei
Which Candida species has some strains which are resistant to fluconazole?
C. glabrata
Which Candida species is completely resistant to fluconazole?
C. krusei
What is the most common type of exogenous Candida infection?
Nosocomial (in hospital)
Which Candida species is the most common culprit for hospital outbreaks?
C. albicans
Why is Candida auris a recent nosocomial issue?
Colonises people very quickly
Persistent in environment
Highly resistant to many antifungals
What are some oral manifestations of candidiasis?
Acute pseudomembranous candidiasis (detachable plaques)
Chronic pseudomembranous candidiasis - AIDS associated
Chronic mucocutaneous candidiasis
Angular cheilitis
What is chronic pseudomembranous candidiasis associated with?
AIDS
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
Describe angular cheilitis.
4-8% of infants
HIV+ = much increased risk
Affects corners of mouth, across lips and tongue
How does Candida infection affect interdigital regions?
Moist, wet, sore
What causes onychomycosis and paronychia and how do they present?
Candida
Discolouration and swollen and red bed of nails
Describe intertrigo.
Candida infection
Submammary region
Red, scaly with satellite lesions
What are risk factors for Candida infection?
Occlusion of skin (fingerwebs, finger nails, obesity)
Wetness in folds
Diabetes
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)
What are some disposing factors to systemic candidiasis?
Age
Immune state or suppression
Antibiotics
Abdominal surgery
Catheters
Prolonged hospitalisation
What areas are affected in systemic candidiasis?
Blood
Lungs
Internal organs
Skin
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)
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
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
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
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
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
Describe cryptococcosis.
Chronic
Subacute to acute pulmonary infection resulting from inhalation of Cryptococcus yeasts
On dissemination, shows predilection for CNS –> cryptococcal meningtitis
What is Cryptococcus neoformans associated with?
Large amounts of bird droppings
Which patients are at major risk of cryptococcosis?
HIV/AIDs
Which Cryptococcal yeast is associated with large amounts of bird droppings?
Cryptococcus neoformans
Which Cryptococcal yeast is more likely to infect healthy people and what is it associated with?
Cryptococcus gattii
Trees and soil
In what form does Cryptococcus grow?
Yeast form only - no hyphae
What is the major virulence factor of Cryptococcus?
Capsule - protective against drugs and prevents phagocytosis
Are mould infections endogenous or exogenous?
Exogenous
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
What kind of infections do dermatophytes cause?
Tinea (superficial infections) - “ringworm fungi”
Who can be affected by dermatophytes and how is it spread?
Infects healthy and immunocompromised people
Spread between people, animals and soil
What organism causes tinea?
Dermatophyte (mould)
Why do dermatophytes affect hair, skin and nails?
Uses keratin as a substrate
What is the commonest cause of skin and nail mould infections?
Trichophyton rubrum
What is the commonest cause of hair/scalp mould infection?
Trichophyton tonsurans
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
What is a kerion?
Painful inflammatory mass where the body is fighting infection
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
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
What are the two main types of mould?
Dermatophytes
Aspergillus
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
Name some of the commonest Aspergillus species.
A. fumigatus
A. flavus
A. nidulans
A. niger
A. terreus
Why are Aspergillus species referred to as a “species complexes”?
Each species comprises of closely-related organisms that can only be distinguished genetically
What is allergic aspergillosis?
Temporary presence of Aspergillus in respiratory tract in healthy hosts
Mainly affects agricultural and horticultural workers
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
Describe invasive aspergillosis.
Caused by A. fumigatus
Has a pulmonary focus but can disseminate
Linked to immunocompromised hosts
What is systemic aspergillosis?
When invasive aspergillosis leaves lungs and spreads to other organs, brain
Only immunocompromised hosts
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
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
Which Aspergillus species is most common?
A. fumigatus
