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Micro - mycology


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What are the 3 morphological types of fungi?
Describe the yeast form.
*reproduce by budding
Describe general features of molds
*filamentous w/hyphae
*reproduce via spores
What are the two forms dimorphic fungi take? What spurs the transition? Name 3 dimorphic fungi.
1.mold at ambient temp (~25); has infectious spores
2.yeast at body temp; pathogenic form
*histoplasma, blastomyces, coccidioides
What are conida?
The spores produced by mold fungi.
Describe a structural variation found among hyphae.
*aseptate: no cross walls present (is multinucleate)
*septate: has cross walls
What is a dematiatious fungus? What's the prognosis with it?
*has black and brown pigmented hyphae
*difficult to treat - poor prognosis
What fungus might be visulaized with an india ink stain? What feature of this fungus would be particularly evident?
Cryptococcus; reveals capsule
What substances are present in the cell wall and in the cytoplasmic membrane of fungi that are not found in bacteria?
*wall: chitin
*membrane: sterols
Antibacterials are generally not effective against fungi, but there is an exception. What is it?
PCP is susceptible to SMZ-TMP.
In general, bacteria are larger than yeasts.
False: yeasts are larger than bacteria.
What is the mechanism of action of amphoteracin B?
It binds to ergosterol in the cell membrane - this causes loss of membrane integrity.
Amphoteracin B is a broad spectrum anti-fungal and effective at killing - so why is its use reserved?
It is very toxic, especially to the kidneys.
What modifications may make amphoteracin more widely used? What is the drawback to these changes?
New liposome technology reduces toxicity, but is extremely expensive.
What is the mode of action of the azoles? What fungi are they effective against?
*inhibit ergosterol synthesis
*active against yeasts, Aspergillus, and some dimorphics
What is the mode of action of the echinocendins?
Block glucan synthesis - glucan is an impt component of the cell wall and is used in the synthesis of chitin.
What form are dermophytes? What is their site of infection?
They are molds that produce keratinases and target keratinized tissues (hair, skin, nails)
Name 3 common maladies caused by dermophytes.
1.Ring worm
2.Athelete's foot
3.Jock itch
Dermophytes are generally resolved by an antibody-mediated immune response.
False: B/c they generally do not invade tissue, dermophytes seldom elicit an immune response of any variety.
What are the 3 genuses of dermophytes that commonly affect humans?
What form is Sporothrix schenckii? How is it commonly contracted?
*dimorphic; cigar-shaped as yeast and thin, septate hyphae with pyriform conidia as mold
*infects SC tissue after trauma with splinters or thorns
What happens after sporothrix enters the skin?
*forms a papule
*can ascend along lymphatics
Patients with systemic infection by dimorphic fungus must be kept in negative pressure rooms to prevent spread of infection.
False: There is no p-p spread with infections of this type. The infection is acquired by inhalation of spores from the environment.
Where is coccidioides considered indigenous? What effect does this environment have on their life cycle?
In arid, or semi-arid regions like the american SW and northern Mexico. Dessication leads to formation of infectious spores.
The yeast form of coccidioides, the spherule, contains infectious endospores.
False: contrary to their name, endospores are not true spores and are not infectious.
What environmental factors favor the growth of Histoplasma? Which group of hobbyists are likely to become infected?
*bird and bat feces
Which part of the Histoplasma mold form is infectious - microconidia or macroconidia?
Microcondida are infectious; the tuberculated macroconidia are not.
Histoplasma is prevalent in what geographical areas?
Lower Mississippi River valley, Caribbean basin.
What does the yeast form of histoplasma look like? In what cell can this form be found?
*small and lemon-shaped
*seen in macrophages
The CXR of a patient with histoplasma can be confused with miliary TB. Why is this?
The presence of widespread granulomatous lesions in the lung fields.
Systemic Histoplasma is seen in immunocompromised patients. Specifically, what population and how is the disease manifested?
*HIV pts w/CH4+ < 100
*chronic pulmonary presentation
How can histoplasma be diagnosed?
*blood cultures
*bone marrow cultures
Name 4 infections that present similar to TB and can be differentiated based on bone marrow culture.
What is characteristic of the yeast phase for Blastomyces?
Broad-base budding
How can blastomycosis present in its disseminated form?
*chronic pulmonary form
*may affect any part of the body: skin lesions, osteomyelitis, and prostate

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