Which organism is a non-dimorphic fungus commonly associated with concentrated bird droppings and can cause meningitis in immunocompromised individuals?

• A. Coccidioides immitis
• B. Cryptococcus neoformans
• C. Histoplasma capsulatum
• D. Candida albicans

Answer: (B)

The main idea is recognizing a non-dimorphic environmental fungus that can cause meningitis in people with weakened immune systems and is classically linked to bird droppings. Cryptococcus neoformans fits this description: it remains a yeast (not a mold) at body temperature, and it is commonly found in soil contaminated with pigeon droppings. Inhalation of the organism can lead to a latent lung infection and subsequent spread to the central nervous system, where it causes meningitis, a classic problem in immunocompromised individuals such as those with AIDS. The organism’s polysaccharide capsule is a key virulence factor, making it harder for immune cells to clear the infection; this capsule is also what clinicians target with diagnostic tests like the India ink stain (encapsulated yeasts appear as a clear halo) and capsule antigen detections.

Other fungi mentioned have different features. For example, some are dimorphic, switching between mold forms in the environment and yeast forms in tissue, and are associated with different ecological niches. Candida albicans is a yeast that can cause opportunistic infections but is not characteristically tied to bird droppings or meningitis as a classic presentation in immunocompromised hosts.