MICROBIOLOGY - Fungal and other Infections Flashcards
What is the mechanism of action of polyene groups (amphotericin and nystatin)
Binds to ergosterol and alter’s ionic transport and permeability of cell wall leading to cell lysis.
What is the mechanism of action of imidazole?
Inhibition of ergosterol production by affecting the cytochrome p450 pathway
Which imidazole is effective against aspergillus?
Itraconazole
Amphotericin (polyene group) is also effective.
What is the main side effect of imidazole ?
What is the main side effect of polyene groups?
- hepatotoxicity
- nephrotoxicity and anaemia
What is candida albicans cultured on?
Sabouraud’s glucose media in 24-48 hours.
When is candida albicans commonly seen in ophthalmology (4)
- Cataract surgery
- Corneal transplant
- Therapeutic contact lenses
- Steroids/immunosuppresion
What are the ocular manifestitations of candida albicans?
- Candidal chorioretinitis
- Candidal endophthalmitis (endogenous)
What are the clincial findings in fungal infections? (2)
- pseudophyphae in corneal stroma
- feathery-edged infiltrate with satellite lesions
What is the pathogenesis of aspergillus/fusarium keratitis?
- Hyphae which contain proteases penetrate through stroma into the AC (hypopyon)
- C-type lectins bind to cell wall components (beta-glucan and alpha-mannose) leading to chemotactic/cytokine release
What are the different types of acanthomoeba?
Protozoa
1. A castellani
2. A. polyphaga
What are the clinical features of acanthomoeba keratitis
- Ring infiltrate
- Perineural infiltrate
What is the pathogenesis of acanthomoeba keratitis? Which is the most potent form?
- Atachment of amoeba by increased expression of mannose-binding protein
- Expression of proteases which destroy the epithelium and upregulate MMPs promoting invasion and ulceration
- Breaches bowman’s layer and degrades stroma and causes radial neuritis
T4 is the most potent form
What is the main mechanism of transmission of toxoplasma gondii?
- Ingesting food contaminated with cat faeces
- Undercooked meat
- Maternal transmission
What are the virulence factors / pathogenesis of toxoplasmosis?
Toxo proteins activate toll-like receptors on monocytes and dendiritic cells to produce IL-2 and an indirect T cell response
Within the cell, the toxoplasma resides in a vacuole resistant to lysosomal destruction –> survives best in brain and retina.
Whats the main differences between toxocariasis and onchocerciasis?
CAUSE/PATHOGEN, VIRULENCE/PATHOGENESIS, TREATMENT
Cause
Toxocariasis - canine parasite transmitted by dogs/cats (helminth)
Onchocerciasis - Simulium blackfly acts as vector and breeds in rivers, transfers infected larvae into human host
Pathogenesis
Toxocariasis: IgE mediated response with eosinophilia
Onchocerciasis: simulium blackfly vector
Treatment
Toxocariasis: Tiabendazole
Onchocerciasis: Doxycycline, Ivermectin
- What is the cause of loa loa
- What is the pathogenesis of loa loa
- What is the diagnosis of loa loa
- What is the treatment of loa loa
Cause: Chrysop fly vectors -
Pathogenesis: calabar swellings form by eosinophilia
Diagnosis: microfiariae in blood
Management: –
What are the three forms of toxoplasmosis gondii?
- Oocyst/sporozoites - between 10-12 microns, soil form
- Tachyzoite - between 4-8 microns (smallest), infectious form
- Bradyzoite -between 10-200 microns, latent form (tissue cyst)
What is the different forms of acanthamoeba? Which is the most common genotype?
Biphasic lifecycle
1. Trophozoite - active stage
2. Cyst form - physiological inert
Most common: T4.
What is the most common genotype of acanthamoeba keratitis?
T4 genotype
When does congenital infection occur in toxoplasmosis? When mother is previously exposed to toxoplasma or becomes infected during first time in pregnancy?
Becomes infected during first time in pregnancy
What does candida stain?
What does candida culture?
Periodic Acid Schiff and Grocott’s methenamine silver stain
Grows on Sabouraud’s dextrose agar (better than blood)
Whats the difference between aspergillus and candida for corneal disease in terms of risk factors?
aspergillus - trauma involving plants
candida - immunosupressed/ocular surface disease
What are the 3 classifications of fungi with examples?
- molds (filamentous fungi) - Fusarium
- Yeasts - Candida
- Dimorphs (mold or yeast) - histoplasma
What are the ocular manifestations of toxocara (3)
Only elicit response when they die.
1. Low grade fibrous retinal involvement
2. Rapid retinal inflammation with eosinophilia
3. Vitritis and pars planitis
What type of parasite is
1. Toxocara
2. Acanthomoeba
3. Toxoplasmosis
4. Schistosoma
- Toxocara - Nematode
- Acanthamoeba - Protozoa
- Toxoplasmosis - Protozoa
- Schistosoma - Trematode
In which trimester is congenital toxoplasmosis most severe?
In which trimester is highest risk of developing congenital toxoplasmosis
most severe: First
most common: Third.
What is the most common ocular manifestation of lyme disease?
intermediate uveitis
What are the different forms of candida?
Yeast: Ovoid-shaped, budding, infects cornea
Pseudohyphae: formed in corneal stroma
True hyphae:
Parinaud’s oculoglandular syndrome is caused by which organism?
Bartonella (cat-scratch disease)
Granlumatous conjunctivitis and ipsilateral swallen pre-auricular lymph nodes
