Week 10: 10.1 microbio pt 2 highlights Flashcards
Opportunistic fungi usually infect who?
Immunocompromised
How is Candida albicans diagnosed?
KOH wet mount from skin scrapings/sample shows characteristic budding yeast +/- pseudohyphae (or hyphae)
List key facts abt Histoplasma capsulatum
1) Caused by Histoplasma capsulatum
2) Inhaled from soil with bird or bat droppings
3) Oval budding yeast inside macrophages in tissues
4) Dxd with antigen and antibody detection (usually use >1 test)
Describe how to Dx histoplasmosis
1) Antigen detection: Histoplasma antigen detection EIA for urine, blood
2) Antibody detection (e.g., serology) may also help
Cryptococcus:
1) What type of organism? How is it transmitted?
2) What does it usually cause?
1) Encapsulated yeast; bird droppings
2) Meningitis/encephalitis and pneumonia
How is cryptococcis diagnosed?
Diagnostic tests (multiple); Dx supported by ID of of encapsulated yeast cells or cryptococcal antigen
[in normally sterile tissues]
CNS (meningoencephalitis): List the 3 tests involved in Dx
1) Definitive diagnosis established by CSF culture
2) Cryptococcal antigen (CRAg) detected in CSF and/or serum
3) India ink
How do you Dx pulmonary cryptococcus?
Sputum/respiratory specimen culture organism isolation
How do you Dx disseminated cryptococcus?
-Blood culture, serum CRAg testing helpful
-Associated skin lesions are common – biopsy would show Cryptococcus
Pneumocystis:
1) What does it cause?
2) How to Dx?
1) Pneumonia (Pneumocystis jirovecii pneumonia [PCP]) illness in immunocompromised patients
2) Cannot be cultured; staining or PCR of respiratory specimens
Describe special staining* with microscopy of respiratory specimens for pneumocystis
1) Induced sputum rapid and least invasive
2) BAL is is highly sensitive/specific (nearly 100% in immunosuppressed)
3) Biopsy (rare)
Pneumocystis:
1) What is increasingly being used as preferred test over microscopy of stained secretions? Why?
2) What is not specific but helpful as an adjunctive test to help support diagnosis in some situations?
1) PCR testing of respiratory specimens; most sensitive/ specific
2) Serum (blood) Beta-D-glucan antigen assay
Opportunistic Fungi: Aspergillus (invasive)
Describe the first step of testing for it.
Obtain noninvasive tests: serum biomarkers + sputum
a) Serum biomarkers: Antigen detection (via Beta-D-glucan assay or Galactomannan assay (not perfectly specific)) OR PCR (detects DNA)
b) Sputum for fungal staining and culture
Aspergillus: What is the second step of Dx?
If diagnosis cannot be established by noninvasive methods, then more invasive approach to obtain specimens is indicated when feasible:
Briefly describe how we contract Ascaris (roundworms; a helminth)
Adult worms live in human intestines and steal food
eggs excreted in human stool contaminate food/water
Ascaris (roundworms): Pulmonary ascariasis:
1) Who is more likely to get this form?
2) What can be seen in someone whose been exposed for the first time within weeks prior to onset of Sx?
3) How is definitive Dx made?
1) First Ascaris exposure
2) Eosinophilia
3) Ascaris larvae visualization on microscopy (Stool examination NOT helpful)
Ascaris (roundworms): Intestinal ascariasis:
How do you definitively Dx this form?
O&P stool microscopy visualizing Ascaris ova (eggs) or by examination of adult worms
-Microscopy will miss early disease, including during respiratory symptoms
What are Hookworms?
Ancylostoma (2 species) and Necator americanus
Hookworm life cycle:
1) Typically*, larvae _________________ after stepping on contaminated soil/sand/feces.
2) Which form can also be acquired by ingestion of larvae in food/water?
1) penetrate skin
2) Ancylostoma
Hookworms: How to Dx?
1) O&P stool microscopy: visualize eggs in stool
2) Stool PCR (better sensitivity)
3) Other common findings: eosinophilia, anemia
Enterobiasis (Pinworms):
1) Where are the eggs?
2) What does this cause?
1) Laid on perianal skin
2) Perianal pruritus
Enterobiasis (Pinworms):
1) Worms/eggs usually not found in _____________.
2) Diagnosis established by finding what? What is a common method of this?
3) What Sx is rare?
1) stool
2) adult worms or eggs on perianal skin; tape test
3) Eosinophilia is rare
What are interfering factors for?:
1) Bacteria detection
2) Parasite detection
1) Abx + urine shouldn’t be mixed w. stool
2) Recent barium studies
