100+ Free Cert ID(SA) Path Practice Questions

Explanation: Capnocytophaga canimorsus is a capnophilic, spindle-shaped (fusiform) gram-negative bacillus residing in the oral flora of dogs and cats. It causes fulminant sepsis, purpura fulminans, and DIC particularly in splenectomised or immunocompromised patients following canine bites or scratches. Gliding motility on agar and requirement for CO2 are key laboratory characteristics.

Explanation: Candida auris typically grows as yeast cells that fail to form pseudohyphae or hyphae on Cornmeal agar (unlike C. albicans or C. tropicalis). It is distinctive for its thermotolerance (grows well at 40-42°C) and osmotolerance (grows in broth containing 10% NaCl and high glucose), properties used in selective enrichment media.

Explanation: Mayer's mucicarmine stain specifically binds to acidic mucopolysaccharides in the capsule of Cryptococcus neoformans and Cryptococcus gattii, staining the capsule bright rose-red to magenta. This distinguishes Cryptococcus from other non-capsulated yeasts in tissue sections.

Explanation: At 25°C (mold phase), Histoplasma capsulatum produces characteristic large (8-15 µm), spherical, thick-walled macroconidia with finger-like projections (tuberculate macroconidia), alongside small microconidia (2-4 µm). In tissue or at 37°C, it converts to small intracellular oval yeast cells (2-4 µm).

Explanation: Enterobius vermicularis (pinworm) female worms migrate to the perianal area at night to deposit asymmetrical, flattened-on-one-side eggs. Direct stool examination is insensitive (<5-10% yield). The cellulose tape (Scotch tape) test applied to the perianal skin upon waking in the morning is the gold standard diagnostic method.

Explanation: Legionella pneumophila is an obligate fastidious gram-negative bacterium that requires L-cysteine and soluble iron (ferric pyrophosphate) for growth. BCYE agar supplies these essential nutrients while activated charcoal neutralizes toxic peroxides and fatty acids.

Explanation: GMS stain selectively colors the cell walls of Pneumocystis jirovecii cysts black. They appear as round, crushed-ball or cup-shaped cysts measuring 4-6 µm in diameter, frequently featuring a characteristic dark focal thickening ('parentheses' or central spot).

Explanation: Aspergillus fumigatus is characterized morphologically by columnar conidial heads with uniseriate phialides arising directly from the upper two-thirds of a dome-shaped vesicle. Tissue sections display hyaline, septate hyphae branching dichotomously at acute (45-degree) angles.

Explanation: Strongyloides stercoralis is unique among intestinal nematodes because eggs hatch into rhabditiform (L1) larvae within the intestinal lumen. Stool microscopy shows motile larvae featuring a short buccal capsule/cavity and a large, prominent genital primordium (distinguishing them from hookworm larvae, which have a long buccal cavity and indistinct genital primordium).

Explanation: Not all isolates of Corynebacterium diphtheriae carry the tox gene (introduced by a lysogenic beta-bacteriophage). Phenotypic verification of diphtheria toxin production requires the Elek immunodiffusion test (precipitin lines formed between antitoxin strip and growing strain) or detection of the tox gene via PCR.