Fungi Flashcards
Which bacteria are able to produce penicillin?
Penicillum Chrysogenum
How do fungi reproduce?
Sexually and asexually
How do moulds reproduce?
by producing spores
which domain of life do fungi belong to?
Eukaryotic
what are the benefits of fungi/yeast
- alcohol beverage production
- antibiotic production
- bread
- recombinant proteins
- enzymes
how do fungi grow?
they grow as single cells
how do moulds grow?
overlapping and interlinking hyphal filaments
what is the asexual mode of reproduction used by fungi?
budding / fission
define mycoses
infection caused by any fungus that invades the tissues
or
diseases caused by fungal infections
what are the different types of mycoses?
1- superficial: white Piedra/ pityriasis versicolor
2- cutaneous: tinea pedis/ onychomycosis/ tinea capitis
3- subcutaneous: chromoblastomycosis/ mycetoma
4- systemic: blastomycosis/ histoplasmosis/ coccidiomycosis
list 3 oppotunistic fungal infections
1- candidiasis
2- aspergillosis
4- pneumonia
describe the structure of a yeast cell
oval with a rigid cell wall
what are the components of a yeast cell wall?
50-60% glucan
(beta-1,6-glucan/beta-1,3-glucan/beta-1,6 complexed with chitin)
25% polysaccharides
15-23% mannan
1-9% chitin
what are the three types of glucan in a yeast cell wall
beta-1,6-glucan
beta-1,3-glucan
beta-1,6 complexed with chitin
what is the role of mannoproteins in the cell wall?
they form a fibrillar layer that radiates from an internal skeletal layer that is formed by polysaccharides of the cell wall which limits wall permeability to solutes by covalent bonds
what would happen if the cell wall of fungi was removed?
it would leave an osmotically fragile protoplast which will burst if not maintained in an osmotically stable environment
what is a protoplast?
a cell with a removed cell wall
what is the role of beta-1,3-glucan in the cell wall of fungi?
1- provides physical protection
2- maintains osmotic stability
3- it is a scaffold for proteins
4- it mediated cellular communication
5- it is the site of enzymatic reactions
what is the periplasmic space?
thing region that lies below the cell wall
what is the plasmalemma?
phospholipid region located directly below the periplasmic space
what is the composition of plasmalemma?
- phospholipids
- lipids
- proteins
- sterols
why does the nuclear membrane of the fungal cell contain pores?
to allow communication between the nucleus and the rest of the cell
what are the mitochondrial enzymes and where are they located within the mitochondria?
- Matrix: Krebs cycle enzymes
- inner membrane: electron transport & oxidative phosphorylation enzymes
- outer membrane: lipid biosynthesis enzymes
TRUE OR FALSE:
the mitochondria has its own DNA and is capable of synthesizing its own proteins, known as mitoribosomes
طبعا صح يعني -.-
what are polysomes?
ribosomes of the fungal cell which are strung together by mRNA
they are also the site of protein biosynthesis
Draw a fungal cell
you should’ve drawn it cheater
what are the classes of antifungal drugs?
- Polyene antifungals
- Azole antifungals
- Echinochandins
- Synthetic antifungals
1- what is the mechanism of action of polyene antifungals?
2- name two polyene antifungal drugs
1- binds ergosterol, the dominant sterol in fungal cells, thus increasing membrane permeability by formation of pores and allowing intracellular components to escape
2- amphoterecin b / nyastatin
1- what is the mechanism of action of azole antifungals?
2- what are the subclasses of azole antifungals?
3- name two azole antifungal drugs
1- interfere with ergosterol biosynthesis by binding to cytochrome P450mediated enzyme (14 alpha demethylase), this prevents lanosterol methylation which prevents lanosterol from becoming ergosterol. thus, lessening the amount of ergosterol in cell wall leading to membrane instability, growth inhibition and cell death
2- imidazoles / triazoles
3- ketoconazole / itraconazole
1- what is the difference between imidazole antifungals and triazole antifungals?
2- give an example of an imidazole and a triazole
1- imidazoles have two nitrogen atoms in the 5 membered sugar whereas triazoles have 3 nitrogens
2- imidazole: ketoconazole
triazole: itraconazole/ voriconazole
1- what is the mechanism of action of echinocandins?
target the synthesis of b-1,3-glucan which is the major polymer of the cell wall as it provides physical protection, maintains osmotic stability, regulates cell shape..etc therefore inhibition of its synthesis disrupts the structure of the growing cell wall resulting in osmotic instability and intracellular components would leave the cell leading to cell lysis
what are the subclasses of echinocandins?
- caspofungin
- micafungin
- anidulafungin
1- what is the mechanism of action of synthetic antifungal agents?
2- what is one example of a synthetic antifungal?
1- synthetic antifungals can work in either of two mechanisms
- disruption of protein synthesis by inhibiting DNA synthesis
- Depletion in the amino acid pools within the cell as a result of protein synthesis inhibition
2- flucytosine
List six fungal pathogens
1- candida albicans
2- aspergillis fumigatus
3- histoplasma capsulatum
4- dermatophytes
5- cryptococcos neoformans
6- saccharomyces cervisae
What morphological forms can candida albicans exist as?
- blastospores
- hyphae
what patients are at risk of candida albicans?
diabetics
burns/wounds
indwelling urinary catheter
cystitis
trauma
underlying disease
organ transplant
how does candida albicans cause disease?
candida albicans is an opportunistic fungal pathogen, which means it is present in the normal microflora, however it only manifests as a disease when the microflora is disrupted
what is thigmotropism?
the ability to sense and respond to changes in surface contours, which aids in finding the line of least resistance in the host tissues
how does candida albicans bind to platelets?
via fibrinogen binding ligands resulting in fungal cell being surrounded by a cluster of platelets
what are the extracellular enzymes of candida albicans? and what is their function?
1- phospholipase A
2- phospholipase B
3- phospholipase C
4- lysophospholipase
their function is to aid adherence and degredation of IgG/IgA immunoglobulins
what are the most clinically common candida species?
candida albicans candida glabrata (resistant)
who is at risk of candida parapsillosis?
neutropenic patients
patients on broad spectrum antibiotics
ICU patients
Patients on parenteral nutrition
catheter associated
What can disrupt the normal flora?
- *1- antimicrobial agents:** allows candida proliferation on mucosa and maceration of skin
- *2- decreased t cell immunity**: allow candida proliferation on mucosa
- *3- neutropenia:** allows candida to escape from gut to bloodstream
- *4- central venous catheter:** allows entry to blood stream
what is the main host defense against candida albicans?
t cell mediated immunity
and neutrophils in mucosa
why is it that HIV patients have frequent oropharyngeal and vaginal candidiasis?
because HIV patients have low counts of CD4 lymphocytes making them susceptible to candidal infections
in a neutropenic patient, where does candida occur?
eyes/kidneys/heart/brain/liver/spleen
how is candida diagnosed?
scrapings/ blood culture/ germ tubes for differentiation
what is candidemia?
A Candida bloodstream infection
what are the symptoms of candidemia?
candidemia symptoms depend on the end organ and can manifest as meningitis or chorioretinitis abscess
who is at risk of cryptococcus neoformans
AIDS
Hematologoic malignancies
transplant
corticosteroids
immunosuppressant drugs
what is the virulence factor of cryptococcosis?
polysaccharide capsule, which inhibits phagocytosis of immune responses thus downregulating Th1 mediators development
how is cryptococcosis diagnosed?
lumbar puncture where fluid will show lymphocytes/ high proteins/ decreased glucose
how is cryptococcosis treated?
amphoterecin B + flucytosine for two weeks
after that, fluconazole for a few months
how does cryptococcus neoformans protect its cell wall?
by producing melanin that resist enzyme degradation of the host immune response
what are the most common aspergillus causing pathogens?
Aspergillus fumigatus + aspergillus flavus
who is at risk of aspergillus?
neutropenic
corticosteroids
transplant
immunosuppressant drugs
how do aspergillus species cause disease?
after entry to the body, they germinate and turn into hyphae which invade tissues thus causing disease
main host defenses against aspergillus
- neutrophils
macrophages
how do neutrophils defend against aspergillus
they line up along their surfaces & secrete reactive oxygen intermediates that kill the organism
how do macrophages defend against aspergillus?
pulmonary macrophages phagocytose and kill conidia but unable to kill hyphal forms
what damage does aspergillus cause?
tissue infarction/ haemorrhage/ necrosis
how is aspergillus diagnosed?
chest radiograph
computed tomography scan
tissue biopsy
how is aspergillus treated?
amphoterecin b
echinocandin
define dermatophytes
they are keratinophilic fungi that metabolize keratin, which is abundant in the skin
what fungal pathogens cause tinea pedis (athlete’s foot)?
- epidermophyton floccosum
- trichophyton rubrum
are tinea infections contagious?
yes
