AP-Micro Microbiology: Mycology and Parasitology 2 — Questions and Answers
Question 1: Which fungal structure is responsible for asexual reproduction by producing chains of spores through budding at the tip?
- Ascospore
- Conidiophore (Correct answer)
- Zygospore
- Basidiospore
Correct answer: Conidiophore
Conidiophores are specialized hyphae that bear conidia (asexual spores) at their tips through a budding or fragmentation process.
Question 2: Plasmodium falciparum causes the most severe form of malaria primarily because it:
- Infects only reticulocytes
- Infects red blood cells of all ages and causes cytoadherence (Correct answer)
- Produces a dormant liver stage called hypnozoites
- Is transmitted by Culex mosquitoes
Correct answer: Infects red blood cells of all ages and causes cytoadherence
P. falciparum can infect erythrocytes of all ages and causes infected cells to adhere to capillary walls, leading to microvascular obstruction and cerebral malaria.
Question 3: The term 'dimorphic fungus' refers to an organism that:
- Reproduces both sexually and asexually
- Exists as a mold at 25°C and a yeast at 37°C (Correct answer)
- Has two distinct nuclear types in one cell
- Forms both hyphae and rhizoids simultaneously
Correct answer: Exists as a mold at 25°C and a yeast at 37°C
Dimorphic fungi switch between mold form (at environmental temperatures ~25°C) and yeast form (at body temperature ~37°C), which is critical to their pathogenicity.
Question 4: Entamoeba histolytica causes disease primarily by:
- Producing neurotoxins that paralyze the intestinal wall
- Secreting proteases that lyse intestinal epithelial cells (Correct answer)
- Blocking bile ducts with cysts
- Stimulating excess mucus production in the colon
Correct answer: Secreting proteases that lyse intestinal epithelial cells
E. histolytica trophozoites secrete cysteine proteases and form flask-shaped ulcers in the colon by lysing and invading intestinal epithelium.
Question 5: Which laboratory test is most useful for diagnosing invasive aspergillosis in an immunocompromised patient?
- India ink preparation of CSF
- Galactomannan antigen detection in serum (Correct answer)
- KOH preparation of skin scraping
- Germ tube test on blood culture
Correct answer: Galactomannan antigen detection in serum
Galactomannan is a cell wall polysaccharide released by Aspergillus during growth; its detection in serum is a sensitive marker for invasive aspergillosis.
Question 6: Toxoplasma gondii can cause severe congenital disease because:
- It is transmitted via the fecal-oral route between neonates
- Tachyzoites cross the placenta and infect fetal tissues during primary maternal infection (Correct answer)
- Bradyzoites are uniquely heat-stable and survive pasteurization
- It invades the placenta only in immunocompetent mothers
Correct answer: Tachyzoites cross the placenta and infect fetal tissues during primary maternal infection
During primary maternal infection, tachyzoites disseminate hematogenously and can cross the placental barrier, infecting the developing fetus and causing chorioretinitis, hydrocephalus, and calcifications.
Question 7: The cell wall component unique to fungi that is absent in humans, making it a key antifungal drug target, is:
- Peptidoglycan
- Ergosterol
- Glucan (β-1,3-glucan) (Correct answer)
- Chitin
Correct answer: Glucan (β-1,3-glucan)
β-1,3-glucan is a major structural component of the fungal cell wall absent in human cells; echinocandins (e.g., caspofungin) inhibit its synthesis.
AP-Micro Microbiology: Mycology and Parasitology 2
Which fungal structure is responsible for asexual reproduction by producing chains of spores through budding at the tip?