Microbiology Flashcards

An encapsulated yeast from CSF is urease positive and produces brown colonies on birdseed agar. What is the organism?

Answer: Cryptococcus neoformans

C. neoformans is urease positive and has phenoloxidase that forms melanin on birdseed agar.

Which rapid test presumptively identifies Candida albicans after 2-3 hours of incubation in serum at 37°C?

Answer: Germ tube test

C. albicans forms germ tubes without constriction at the point of origin within 3 hours.

On a peripheral blood smear, crescent- or banana-shaped gametocytes are characteristic of which species?

Answer: Plasmodium falciparum

P. falciparum gametocytes are crescent-shaped, a key diagnostic feature.

A urine culture is plated with a 0.001 mL calibrated loop and grows 50 colonies. What is the colony count?

Answer: 50,000 CFU/mL

Multiply colonies by 1,000 for a 0.001 mL loop: 50 × 1,000 = 50,000 CFU/mL.

What blood-to-broth ratio is recommended for adult blood culture bottles to dilute inhibitory substances?

Answer: 1:5 to 1:10

A 1:5 to 1:10 ratio dilutes antibodies, complement, and antibiotics in the blood.

A mold shows septate hyphae with acute-angle branching and uniseriate phialides on the upper two-thirds of the vesicle. What is the likely identification?

Answer: Aspergillus fumigatus

A. fumigatus has uniseriate phialides covering the upper portion of the vesicle, pointing upward.

A pear-shaped flagellate with two nuclei and a sucking disk shows 'falling leaf' motility in a stool wet mount. What is the parasite?

Answer: Giardia duodenalis

Giardia trophozoites are pear-shaped and binucleate, with a ventral sucking disk and falling-leaf motility.