what are conidia
greek for dust. Sexual spores that arise from the hyphae of the fungi
why is it hard to treat a fungal infection with most anti-protein synthesis antibiotics
because they have multiple RNA polymerases just like we do and ribosomes like ours whihc means that they are not killed by most anti-protein synthesis antibiotics
describe the plant like righid cell wall of fungi
- That cell wall is comprised of an inner glucose polymer which is referred to as a glucan. Glucan is a long linear polymer.
- Outside of the glucose polymer there’s also a mannose polymer that’s usually highly branched and provides a lot of antigenic specificity that we can use both for diagnosis and also for classifying fungi.
what is a major difference between fungi and humans
we have cholesterol as our major sterol in the plasma membrane which holds it together, fungi usually have some form of the sterol ergosterol in the membrane. The only difference between ergosterol and cholesterol is one double bond. However this little difference is enough to provide some drug specificity for therapy.
hyphae vs pseudohyphae
i. Pseudohyphae are simply yeast cells that grow in an elongated manner. The growing tip cell will divide to produce a chain of yeast cells that are in a pseudohyphal conformation. These are elongated yeast cell. If we have pseudohyphal growth, we refer to those colonies as having a pseudomycelium.
ii. If we have regular hyphal growth it’s called a mycelium.
what kind of spore is common in athletes foot
aleurospore
what kind of spore is a jointed spore
arthrospores…these spores that grow within the hyphae and they give a joint-like appearance
histoplasma and cadida albicans exhibit what type of spores
chlamdospores, which are large, round and thick walled spores
if fungus gives rise to a yeast cell what do we call the spore
blastospore
describe the steps of sexual reproduction in fungi
- Two sexes communcate with each other via peptide pheromones
- That stimulate a ras protein kinase cascade that turns on an alternate developmental pathway
- Cell fusion and karyogamy
- Sometimes zygote can grwo and produce more diploid fungi. ultimately, zygote undergoes meiosis
in this fungal sexual cycle, sexual spores are produced in a sac or ascus
ascomycetes and the fungi in this category include Penicillium
When these undergo meiosis, the sexual spores are put on a base or basidium
basidiomycetes and include all mushrooms such as amanitis, porcini, and cryptococcus
Nonseptate fungi which have a very large diameter probably about 5-10 times the diameter of other hyphae.
Zygomycetes are the nonseptate fungi and includes an opportunistic fungus called Mucor.
what role do protein formation play in fungal processes
They secrete cell wall components like enzymes and partly-made polysaccharides that assemble at the growing tip into a cell wall. But in order to eat, some other of those ribosomes in the rough ER get resorted to make different proteins which are transported via vesicles to the same growing tip. These other proteins are secreted as proteases, nucleases, lipases, and carbohydrolases which are the enzymes that can turn decaying organic matter into basic compounds. These secreted proteins also play an important part in the disease process as well. Fungi are also capable of changing their cell types depending on the environment. Not all fungi can do this. But it’s a very important process with respect to the disease processes especially in the case of systemic fungi
what happens when you culture yeast cell on Sabouraud’s agar
it will produce a mold
how do we see fungal infections
- 10% KOH
- Calcofluor: because of chitin fluoureescent stain
- CSF because of polysaccharide capsule
- Silver stain protein
- Gram stain
- UV light/ wood lamp
probably the most lethal drug to fungi but can be lethal to immunocomprised humans with fungal infections is ____ and explain its mechanism
polyenes: 1. Amphotericin B works by incorporating preferentially into ergosterol containing membranes. When amphotericin B incorporates into the cell membrane it forms a pore. The pore renders the cell membrane useless and small molecules leak into the cell. The cell wall won’t protect the fungus because it is very permeable. The cell can’t maintain its osmolarity and it dies. It’s a very effective anti-fungal medication.
2. The only problem with amphotericin B is that whereas it incorporates preferentially into ergosterol-containing membranes, it can still go into cholesterol-containing membranes at a much lower efficiency. However it can still render mammalian cells permeable and therefore dead this way. Obviously your most important cells with respect to transport and permeability are the kidney cells and as a result kidney failure for people treated with amphotericin B is fairly common. Amphotericin B is called “amphoterrible” in the clinic because of its side effects. Unfortunately since most of the fungal infections that require amphotericin B treatment are acquired by immunocompromised patients, you’re making them more vulnerable to side effects since they are already sick. So this is a drug of choice but it’s also a drug of last choice.
how do imidazoles work
ii. Imidazoles are a little bit more benign. These work by inhibiting a cytochrome 450 containing enzyme. Because this enzyme is blocked by imidazole, the fungal cell cannot make ergosterol. If you can’t make ergosterol, you can’t make good membranes. The membranes will be leaky and the cells die. It’s thought that imidazoles may affect steroid metabolism a little bit in some people but generally they are much more benign than polyenes.
how do terbinafine or allylamines work against fungal infections
accumulation of squalene and the prevention of ergosterol biosynthesis.
terbinafine or allylamines. These drugs inhibit squalene epoxidase which is an early enzyme in ergosterol biosynthesis. Allylamines are specific for fungi. There are two modes of action that have been proposed for terbinafine or allylamines.
- One thing that’s believed is that they prevent the formation of ergosterol to some extent.
- But it’s also believed that because fungal cell cannot process squalene due to inhibition, the cell accumulates squalene. Although squalene is an important intermediate, it’s also toxic at high concentrations.
how do echinocandins work?
the penicillin of fungal drugs. Echinocandins inhibit cell wall formation by inhibiting the glucan. Caspofungin and Cancidas are types of echinocandins which are made by Merck.
how does fluorocytosine or Ancobon work
inhibits synthesis of nucleic acids. It’s not all that fungi specific but it seems to work better on fungi than on mammalian cells. Fluorocytosine is often used in combination with other antifungals. However high concentrations of fluorocytosine can be carcinogenic because it inhibits nucleic acid synthesis
what is the fungal name for athletes foot
trichophyton mentagrophytes
what causes the itching in athletes foot
Those secreted proteases are antigenic and cause a Type II hypersensitivity response. As a result of the Type II HS reaction, mast cells come in and you start itching which leads you to scratch.
is ringworm on the beard
b. Tinea barbi
