This site is 100% ad supported. Please add an exception to adblock for this site.

Micro: Oppurtunistic Fungi and Yeast


undefined, object
copy deck
What is the ecology and epidemiology of C. neoformans?
found in soil and associated with pigeon droppings; gains entry into the body via inhalation

there are two forms: cryptococcoma and diffuse penuomonitis; CNS involvement cause Meningitis

risk of developing meningitis is greatly increased in immunodeficient host esp those with Hodgekins, other reticuloedothelial defects, chronic lymphoblastic leukemia, sarcoid, lung carcinoma, SLE and AIDS
What special property C. neofrmans allows it to survive and multiply in such an environment?

ALSO it is able to utilize creatinine as its sole source of nitrogen

reproduces by budding
How is C. neoformans acquired?
inhalation of organism

found in 1 micrometer of soil, allows for easy uptake by alveolar macrophages
What is an important cell component of the yeast C. neoformans?
polysacchride capsule
- fibrils of capsule surround the organism
- fibrils repell India ink --> negative stain

muccicarmie stains the polysacchride capsule
Whay has there been a tremendous increase in the cases of meningitis due to C. neoformans?

How do you treat these cases?
it is the most common clinical presentation esp in patients with AIDS

organism is never completely cleared from the body

lack of effective CMI prevents elimination of orgs from body

treat with amphotericin B + flucystosine
What is the most sensitive and specific test for diagnosing disease due to C. neoformans?

What other method is used to examine CSF in the clinical lab?
Cryptococcal Latex Agglutination Test
- serological test for polysacchride capsule Ag

India ink stain
Diseases cause by C. albicans are quite varied. How is the organism acquired?
acquired endogenously
- exists as normal flora of respiratory, GI, and female genital tracts
- found in all women during pregnacy
- by age 1 every one has positive skin test
What are some of the factors that predispose individuals to infections with Candidiasis?
1) local factors
- disruption of skin; having your hands in water all day; poor fitting dentures

2) intrinsic factors
- age, young childrean more susceptible; pregnancy; diabetes, malignacies, leukemias and lymphomas

3) Extrinsic Factors
- antibiotics; corticosteroids; surgery; trasnplantation (immunosuppressive therapy); oral contraceptive use
Are blood cultures for C. albicans useful as definitive proof of life threatening infections?

If the clinical laboratory tells you that you have grown 10^6 colonies of C. albicans in a urine culture from a patient, is that significant?
Isolation from blood is diagnostic of disseminated infection only

No. Most patients on broad spectrum antibiotics have candidiasis overgrowth
What do you see in a direct mount or histopathology of tissue infected with Candida?
pseudohyphae and budding yeast

germ tubes at 37 degrees
What is Chronic mucocutaneous candidiasis (CMC)?
separate entity which generally begins early in life and is associated with polyendocrine disorders or defects of the immune system

all patients have defects in T-Cell Immunity

never develop life threatening Candida infections
What is Systemic (Disseminated) Candidiasis?
the organism invades the organ system of a debilitated or immunocompromised host; manifest by several life threatening conditions

Candida esophagitis
Candida endocarditis
systemic candidiasis of liver, kidney and bone marrow
How do Aspergillus species act on the lung?
1. may act as allergens causing asthma and bronchitis in sensitized patients - allergic aspergillosis

2. occur as saprophytes in lung cavities or dead areas of lung tissue - aspergilloma

3. may actively invade the living lung parenchyma in pts with reticuloendothelial disease - pulmonary aspergillosis
What is seen in histopathology of apsergillosis?
dichotomous branching 45 angle (septate hyphae)

Allergic Aspregillosis - infiltration of polymorphs and lymphocytes
What factors predispose to the development of an Aspergillus fungus ball?
long term immunosuppresion

old tuberculous or bronchiecstatic cavity, or infarct
What are the factors that predispose to Zygomycosis?
altered metabolism and decrease immunological response

diabetes --> mucormycosis
What is seen int he histopathology of zygomycosis?
hyphae are broad and aseptate

seen as short branche filaments that are often very distorted or collapsed

hypahe contain protoplasm, which stains haematoxylin, or appear empty

walls are very thin
What are the characteristics of the organisms?

Are they septate or non septate?
commonly isolated from soil and water

aseptate and form asexual spores in a sporangium
Of which organ do the zygomycetes have a marked tendency for invasion?
marked tendency to invade blood vessels --> thrombosis, occlusion and infarction by necrosis
What is associated with the pathogenecity of C. albicans?
transformation from a yeast to a hyphal form

Deck Info