Fungal lectures

Question 1

no of fungal species and class

Answer 1

250,000 species but only 180 cause disease in humans or animals.
most fungi are saphrophytes that feed on dead plant or animal materail.

Question 2

eukaryotic characteristics of fungi

Answer 2

1 - membrane bound nucleus with several chromosomes
2 - genomic DNA with introns
3 - plasma membrane and cytoplasmic organelles
4 - membranes contain ergosterols

Question 3

fungal structure

Answer 3

cell wall - predominantly polysaccharides- inner layer of chitin microfibrils, outer matrix of glucans with mannose containing proteins embedded in the cell wall. some yeasts also have a discrete outer polysaccharide capsule.
2 - cytoplasmic membrane, cytoplasm, organelles, nucleus

Question 4

primary fungal morphologies

Answer 4

1 - yeasts
2 - filamentous moulds
3 - dimorphic fungi

Question 5

decribe yeast morphology

Answer 5

1 - oval or round unicellular organisms
2 - multiply by mitosis, either by symmetrical binary fission (schizosaccharomyces pombe) or asymmetrical budding (candida, cryptococcus)
3 - some also grow as short cylinders called pseudohyphae (candida)

Question 6

describe filamentous mould morphology

Answer 6

1 - thin branching multicellular cylinder = a hypha (plural is hyphae)
2 - apical growth, mitosis only occurs at the tip and at side branches
3 - can either be septate with multiple interconnected compartments (aspergillus) or aseptate with many nuclei in a common cytoplasm (mucor)
4 - can form an interwoven mass called a mycelium. when compacted together, layers of hyphae can form fungal tissue in macroscopic structures eg muschrooms.

Question 7

describe dimorphic fungi morphology

Answer 7

1 - either a filamentous mould at 22 degreesC in the environment or a yeast at 37degreesC in the body (eg histoplasma)

Question 8

overview of fungal reproduction - brief

Answer 8

produce spores, small, tough, light fungal cells adapted for dispersal and survival in hostile conditions.
spores can be either asexual or sexual, depending on the state of differentiation of the fungus during production.
asexual state = anamorphic state
sexual = teleomorph state

Question 9

asexual spores - mech of production, examples and function

Answer 9

1 - anamorphic state fungus (asexual/mitotic/imperfect state). produced by mitosis.
2 - yeasts produce internal endospores
3 - moulds produce either external spores = condida/condidium, or internal spores within a sporangium.
4 -asexual spores are for dispersal - germination - multiplication and so colonization.
5 - Deuteromycota group of fungi always exist in the anamorphic state and are incapable of sexual reproduction.

Question 10

sexual spores - mech of production, examples and function

Answer 10

1 - teleomorphic state (meiotic/sexual/perfect state). most fungi exist in a haploid state and will only briefly produce diploid fungi through this sexual reproduction.
2 - sexual structures are produced (motile gametes/specialized sexual hyphae). those from 2 seperate individuals fuse, nuclei fuse to make diploid - chromosome reassortment and recombination - meiotic reduction division to haploid sexual spores.
4 - usually tough and enable organism survival in hostile conditions. germinate once favourable conditions return.

Question 11

method of fungi classification (no details) and where are sexual spores formed?

Answer 11

classified by where the sexual spores are formed. either:
1 - internally in tubular structure called an ascus
2 - externally on a specialised club-like structure called a basidium
3 - or externally as a thick walled structure following fusion of the sexual hyphae.

Question 12

classify fungi

Answer 12

1 - broken down into yeasts, filamentous moulds and dimorphic fungi. each of these can divided into ascomycota, basidiomycota, zygomycota and deuteromycota.
2 - so, structure and reproduction.

3 - ascomycota = both sexual and asexual spores. sexual in an ascus, asexual externally as a conidium.

4 - basidiomycota - only sexual spores, externally on a basidium.

5 - zygomycota - both sexual via external fusion of hyphae, and asexual internally in a sporangium

6 - deuteromycota (imperfect fungi) - no sexual spores, asexual spores produced externally

Question 13

examples of ascomycota?

Answer 13

yeasts - schizosaccharomyces, saccharomyces, pneumocystis, candida

moulds - aspergillus, fusarium, microsporum, trichophyton, epidermophyton.

dimorphic - histoplasma

Question 14

examples of basidiomycota?

Answer 14

yeasts - cryptococcus, malassezia

Question 15

examples of zygomycota

Answer 15

moulds - mucor and rhizopus

Question 16

examples of deuteromycota

Answer 16

dimorphic - coccidioides, paracoccidioidea, sporothrix.

Question 17

how do fungi feed?

Answer 17

secrete enzymes into environment to digest food material, absorb simple molecules through cell wall pores. live in moist environments. hyphae penetrate food material.

Question 18

what are the different lifestyles of fungi?

Answer 18

1 - saprotrophs - feed on dead plants and animals, occasionally cause disease is accidentally implanted of inhaled
2 - parasites of living plants - makor cause of crop disease (ergot?)
3 - parasites of humans and animals, can cause disease.

Question 19

what 6 metabolites produced by fungi are of interest to us?

Answer 19

1 - CO2 - raising bread dough
2 - ethanol - alcoholic drinks
3 - antibiotics - penicillin, cephalosporin, streptomycin
4 - immunosuppressants - cyclosporin
5 - other drugs - ergotamine, ergometrine
6 - toxins - aflatoxins

Question 20

first defense against fungal infeciton?

Answer 20

intact epithelium is key. damage permits invasion then dissemination.
commensal bacterial flora in mouth and genital tract inhibits proliferation of the surface. broad spectrum antibiotics remove this allowing commensal fungi such as candida albicans to flourish.

Question 21

recognition of fungi by the immune system?

Answer 21

macromolecules recognised by PRRs on DCs, macrophages, neutrophils and some epithelial cells - initiate signal cascade - cytokines out for CD4 response - effector cytokines IL-17/23

Question 22

list some fungal PAMPs, their PRRs on DCs and macrophages, the cytokines and cells recruited.

Answer 22

1 - beta-glucan, phospholipomannan, O-linked mannose, N-linked mannose
2 - dectin-1 (- SYK/CARD9/MALT1/NFkB), TLR 2 (for phospholipoannan), TLR 4 (for O-linked mannose), Mannose receptor (for N-linked mannose).
3 - TGFbeta, IL-6/23
4 - Th17 T cells

Question 23

what’s a lectin?

Answer 23

protien that specifically binds a defined carbohydrate structure - ie C-type lectin Dectin-1 that binds beta-1,3glucan in the cell wall.

Question 24

what general categories of disfunction increase susceptability to fungal infection?

Answer 24

1 - impaired fungal recognition
2 - impaired IL-17 immunity
3 - impaired neutrophil number and funciton
4 - impaired T cell and macrophage number or function.

Question 25

causes of impaired fungal recognition?

Answer 25

2 rare inherited genetic disorders predispose to chronic fungal nail infection and or mucosal candida infection
1 - Dectin-1 deficiency - point mutation, premature stop codon in extracellular recognition domain. homozygotes = reduced expression of mutant on blood mononuclear cells , stimulation with beta-glucan produces reduced cytokine secretion (TNFalpha, IL-6/17). frequency of heterozygote carriers is 7% in dutch and 3% in african pop.
2 - otherr mutation is in caspase recruitment domain-containing protein 9 (CARD9). part of signal transduction for dectin-1. homozygous point mutation, premature stop codon, reduced expression, impaired signal, reduced numbers of Th17 CD4s.

Question 26

describe impaired IL-17 immunity

Answer 26

2 mechs, rare and inherited.
1 - deficiency of receptor for IL-17, selective susceptibility to chronic superficial Candida infection in childhood
2 - or autoantibodies vs IL-17/23 to inactivate and also permit chronic superficial Candida infection.

Question 27

describe impaired neutrophil number or function in fungal infection

Answer 27

predisposes to depp fungal infections especially opportunist filamentous moulds.

• severely reduced numbers = neutropenia, frequently following cancer chemotherapy.
• reduced function in inherited disorders ie chronic granulomatous disease. mutation in a gene for neutrophil NADPH oxidase needed to generate superoxide to kill phagocytosed fungi. normally results in aspergillus infection.

Question 28

describe impaired T cell and macrophage number or function in fungal infection

Answer 28

• predispose to superficial and deep yeast infection (candida, pneumocystis, Cryptococcus) and dimorphic fungi which invade the body as yeasts (histopasma). eg Primary (genetic) immuno-deficiency syndromes, immuno-suppressant drug treatment, haematological malignancies, AIDS.

Question 29

3 methods of diagnosis of fungal infection?

Answer 29

1 - in vitro culture from clinicla sample ie bllod, urine, skin scraping, lung biopsy.
2 - detection fo fungal polysaccharide or DNA in clinical sample. ( crytptococcal polysaccharide in blood/CSF, or Pneumocystis DNA in lung fluid.
3 - tissue biopsy for microscopy - morphology used in identification of filamentous fungi.

Question 30

abroad targets of antifungal drugs?

Answer 30

1 - fungal membranes - either ergosterol function or synthesis.
2 - fungal microtubules
3 - fungal cell wall

Question 31

drug classes and examples that target ergosterol function

Answer 31

polyenes - amphotericin, nystatin.

Question 32

drug classes and examples that target ergosterol synthesis

Answer 32

1 - azoles - clotrimazole, fluconazol, voriconazole

2 - allylamine - terbinafine

Question 33

drug classes and examples that target fungal microtubules

Answer 33

griseofulvin

Question 34

drug classes and examples that target fungal cell walls

Answer 34

echinocandin - target synthesis of beta-1,3glucan - caspofungin

Question 35

5 general patterns/methods of fungal infection

Answer 35

1 - fungal toxins in food but no fungus in human - poisinous mushrooms, ergotamine.
2 - commensal infections ad normal flora - normal
3 - superficial fungal infection of dead keratinized tissue
4 - subcutaneous fungal infections
5 - systemic (deep) fungal infections

Question 36

example of a commensal infection

Answer 36

1 - Candida Albicans in throat, gut and vagina.

filamentous oulds not part of normal flora

Question 37

describe superficial fungal infections

Answer 37

in dead keratinized tissues ie skin, nails and hair. - also called ringworm
1 - dermatophyte moulds eg microsporum, trichophyton, epidermophyton.
v common on humans, acquired by sporee either directly (person to person) or indirectly (shared clothing or environment)
- not life threatening as they dont invade deeper tissues
- chronic infections
- non-toxic antigens often induce local hypersensitivity causing increased skin proliferation (flaky scaly), itching, scratching and secondary bacterial infection.
- often difficult to eradicate and can reoccur.

2 - yeast Candida Albicans - disfiguring chronic finger nail infection

3 - yeast Malassezia furfur - causes pityriasis versicolor (blotchy skin rash that doesnt tan). treat with topical Clotrimazole or Terbinafine cream, if necessary oral Terbinafine.

Question 38

Describe subcutaneous fungal infections

Answer 38

1 - low virulence saprotrophs in soil or vegetation, mostly warm climates.
2 - infection via injury and implantation
3 - usually developes slowly and remains localised as a subcutaneous nodule but may spread via lymphatics
4 - ege dimorphic Sporothrix schenckii - invades as yeast at 37degreesC - rose pickers’ disease with nodules that may spread

Question 39

describe systemic (deep) fungal infections

Answer 39

1 - may be confined to site of entry (usually inhaled into lung) or may disseminate. 2 main types - systemic pathogens and systemic opportunists.

2- systemic pathogens - relatively high virulence, inhaled spores into lung, asymptomatic infection of macrophages is common.

3 - systemic opportunists - low virulence, only immunocompromised subjects, lung, para-nasal sinuses, gut, IV lines, not asymptomatic infection of macrophages.

Question 40

6 examples of systemic fungal pathogens and their endemic areas

Answer 40

1 - histoplasma - USA, Africa
2 - Coccidioides - western USA
3 - Paracoccidioides - south america
4 - blastomyces - USA, Africa
5 - penicillium - south east asia
6 - cryptococcus - worldwide

Question 41

4 examples of systemic fungal opportunists

Answer 41

found worldwide
1 - candida
2 - pneumocystis
3 - aspergillus
4 - cryptococcus

Question 42

effect of temperature on Histoplasma?

Answer 42

histoplasma capsulatum, dimorphic fungus in soil or bat droppings in mississippi and ohio valleys. air bourne spores inhaled by bats or close humans.
1 - temp dependent switch in gene expression and morphology
2 - multicellular filamentous mould at 24degreesC releasing asexual spores. unicellular budding yeast at 37degreesC
3 - temp regulates kinases DRK1 and RYP1 to alter pattern of gene expression.
4 - includes expression of alpha-1,3-glucan not recognised by PRRs, fungal hsp60 which binds macrophage surface CD11/18, secreted protease-resistant calcium binding protein (CBP) that facilitates fungal growth within macrophage vacuoles.
5 - persistant infection results in macrophage activation and granuloma formation. inject dead histoplasma antigen under skin to test for past infection.

Question 43

outcomes of histoplasma infection in lung?

Answer 43

1 - asymptomatic - positive skin test only clinical feature - resolved
2 - acute pulmonary (influenza like) disease - lung infiltrates and enlarged hilar lymph nodes - usually resolved
3 - chronic pulmonary disease - chronic lung inflammation, fibrosis and cavitation - progressive incapacity
4 - disseminated disease - focal spread outside lung ie skin, larynx, adrenals. - often fatal.

Question 44

describe candida albicans, infections it causes, conditions these need and treatment.

Answer 44

a commensal yeast on moist mucosal surfaces, usually restrained by host defence and bacterial competition. some strans have raised adhesion and invasion by forming pseudohyphae
1 - oral candidiasis - newborns following inhaled steroids for asthma
2 - vulvo-vaginitis - pergnancy, following antibiotic treatment
3 - urinary tract infection - following uretheal catheter and or prior antibiotics
4 - oesophagitis - advanced HIV infection
5 - candidaemia - IV lines in hospital, IV drug users
6 - disseminated infection - spread via blood to eyes, liver, spleen , heart valves. mainly in the immunosuppressed.

treat with fluconazole or caspofungin
deep infections by other candida species increasingly common in hospitalised. some species resistant to fluconazole ie Candida krusei

Question 45

what is pneumocystis jirovecii, what disease does it cause and how is it treated?

Answer 45

1- yeast, cant culture in vitro yet, human to human transmission, inhalation infection, most children have antibodies by age 3, other species of pneumocystis coevolved with other animals.

2 - requires T cell immunodeficiency ie HIV, leukaemia, lymphoma, immunosuppressants. reinfected, not reactivation of persistant infection.

3 - incidence is seasonal. at least 10% of cases involved coinfection with 2 or more strains.

4 - causes Pneumocystis pneumonia (PCP), a diffuse alveolitis. clusters of oval organisms damage alveolar epithelial cells, becoming filled with protein rich foamy exudate.

5 - impairs exchange hence arterial hypoxaemia. dry cough, progressive breathlessness, fever, weight loss, chest x ray shows diffuse opacification of alveoli.

6 - treat with high dose co-trimoxazole (sulphamethoxazole + trimethoprim) and corticosteroids (prednisolone) to reduce inflammatory response to dying organisms.

7 - in high risk patients its largely prevented by regular low dose co-trimoxazole or inhaled pentamidine.

Question 46

what is cryptococcus neoformans, what disease and conditions needed and treatment?

Answer 46

1 - a yeast saprotroph. worldwide. bird droppings. thick polysaccharide capsule important to its virulence. infection by inhalation
2 - rarely causes pneumonia - in normal or immunosuppressed patients
3 - characteristically causes meningo-encephalitis - in T cell immunodeficiency ie HIV infection, transplants. progressively worsening headache, fever, cognitive impairment, hydrocephalus, coma. despite treatment it has 20% mortality rate and significant neurological disability in survivors

4 - treat with amphoteracin plus flucytosine, followed by high dose fluconazole.

Question 47

what is aspergillus fumigatus, disease, conditions, treatment?

Answer 47

1 - mould saprotroph producing air bourne spores accidentally inhaled
2 - in asthmatics can cause broncho-pulmonary colonisation.
2 - with preexisting lung cavities ie following TB, can cause aspergilloma -a localiszed mass of hyphae
3 - in severe neutrophil deficiency ie following chemo for leukaemia can cause invasive infection of lung or paranasal sinus. has a tendency to spread along blood vessels leading to disseminated infection

4- invasive infection has a very high mortality rate.

5 - treat with amphoteracin or voriconazole. surgery if possible.

Question 48

what is Mucor, what does it cause and treatment?

Answer 48

1- environmental filamentous saprotroph, inhale spores.
2 - disease is Mucormycosis, rare but serious. in poorly controlled diabetes or leukaemia the mould aggressively invades through paranasal sinuses with a very high mortality rate.
3- treat with urgent surgical debridement and amphoteracin.