Fungi II Flashcards
Primary infections by these systemic mycoses causing organisms are usually in the
Lung
Most primary infections are inapparent and self-limiting, recognized only by immune response or
X-ray
Organisms are dimorphic, grow as yeast in tissue and mycelia in culture under usual conditions
Systemic mycoces organisms
The organisms that cause systemic mycoses can be converted to yeast form by culture on
Blood agar
Cultures of mold forms are identified by reaction of soluble antigens with specific antisera. This is called the
Exoantigen test
This is an Oucherlony double-diffusion test; a line of identity is considered
Diagnostically significant
A dimorphic fungus; in tissue Cryptococcus grows as a heavily
Encapsulated yeast
A dimorphic fungus; in tissue Cryptococcus grows as a heavily encapsulated yeast. It is the imperfect stage of a
Basidiomycete Filobasidiella
Like S. pneumoniae, H. influenzae, and N. meningitidis, it is a heavilyencapsulated pathogen that initially infects the respiratory tract and can spread from there to the brain and/or meninges
Cryptococcus
Straddles the boundary between ‘pathogen’ and ‘opportunist’
Candida
In clinical material, can appear as yeast, hyphae, or pseudophyphae
C. albicans
A diagnostic feature which separates C. albicans from other Candida is formation of
“Germ tubes” when yeast are placed in serum
Buds which in serum elongate to form the beginnings of hyphae
Germ tubes
Chronic mucocutaneous candidiasis is a hallmark of defects in
Cell-mediated immunity
Ubiquitous; important pathogens of AIDS patients, transplant recipients, and patients receiving anticancer therapy
Opportunistic fungal pathogens
What are three examples of opportunistic fungal pathogens?
Aspergillus, zygomyces, and pneumocystis carinii
A large genus, ubiquitous in soil and plant material.
-The most frequent pathogen is A. fumigatus although other species are common causes of disease
Aspergillus
The most frequent pathogen of aspergillus is
A. fumigatus
Most aspergillus infections are
Pulmonary
Most aspergillus infections are pulmonary. Infection can be local and non-invasive [‘Aspergilloma’] or invasive and
Necrotizing
Can cause thrombosis, infarction, necrosis, and hemorrhage if they penetrate the walls of a blood vessel, and can also disseminate the infection to other sites
Hyphae
A potent allergen and can cause severe bronchopulmonary reactions in atopic individuals and those heavily [occupationally] exposed
Aspergillus
We can treat aspergillus infections with
Amphotericin/fluorocytosine or one of the newer azoles
Even with treatment, mortality from aspergillus infection is
50-90%
Cause upper or lower respiratory tract disease in immunodeficient patients
Zygomyces [Mucor, Rhizopus]
Tissue hyphae from zygomycetes can be distinguished from those of other fungi by their breadth, sparse/absent septae, tendency to branch at
Right angles
Other fungi tend to branch at
Acute angles
A ubiquitous organism, to which virtually 100% of the U.S. population develops antibodies in childhood
Pneumocystis carinii
Prior to widespread prophylaxis, many AIDS patients developed
Pneumocystis carinii pneumonia [PCP]
Diagnosis is usually made by staining broncho-alveolar lavage fluid
Pneumocystis carinii infection
What are the three genera of opportunists that infect humans?
Encephalitozoon, Enterocytozoon, and Nosemia
Transmission is via contaminated food or water. Life cycle is similar to that of Apicomplexa
Opportunists
The infectious form of the opportunist is the
Spore
Inside the spore wall the cytosol of the microsporidian is continuous with the lumen of a long coiled
Polar filament
When a spore contacts a host cell the filament everts and pierces the host-cell
Plasma membrane
Osmotic flow of water into the spore forces the cytoplasm of the parasite through the polar filament and into the cytosol of the host cell, where it becomes surrounded by
Membrane
Once inside a host cell, a spore develops into a trophozoite and then a
Schizont
After further mitotic and meiotic divisions and formation of zygotes, infectious spores are formed and released by
Host-cell lysis
Have the smallest genomes of any eukaryotes
- 2 mb, smaller than many bacteria
Microsporidia
Mostly intestinal, eye, or systemic infections, although any tissue can become infected
Microsporidia opportunists
An infected expectant mother can infect her fetus transplacentally if the infectio is from
Microsporidia
Used to treat intestinal microsporidia infections
Albendazole
Have been used successfully to treat microsporidial eye infections
Azoles
The “Rose Gardener’s” disease
Sporotrichosis (caused by S. Shcenkii)
Macro life with an Amphipathic ring structure
Amphotericin B
The non-polar side binds tightly to ergosterol in fungal cell membranes and the polar side forms pores for leak from cells
Amphotericin
The crucial link between amphotericin and ergosterol
Mycosamine sugar unit
Drug of choice for almost all life-threatening systemic fungal infections
Amphotericin B
Flucytosine is removed by the kidney in
3-6 Hours
Unlike amphotericin B which binds directly to ergosterol, these drugs target the 3rd step in the biosynthesis of ergosterol
Azoles
Cause accumulation of toxic methylsterols that inhibit membrane enzymes
Azoles
Binds less efficiently to mammalian p450s,offering some specificity toward fungal cells
Azoles
The most potent azole
- wide spectrum
- used orally
Itraconazole
Triazole that least affects the liver enzymes?
Fluconazole
Newest anti-fungal agents
-cell wall disrupters
Echinocandins
Water-soluble semi-synthetic lipopeptide derivative of pneumocandin B
Echinocandins
