**Core Concept**

Nocardia is a genus of weakly staining, gram-positive, catalase-positive bacteria. It primarily affects immunocompromised individuals, causing infections that can range from cutaneous to disseminated disease, including pulmonary and central nervous system involvement. Nocardia species are opportunistic pathogens that thrive in environments with poor sanitation and can be found in soil and water.

**Why the Correct Answer is Right**

Nocardia infections typically present with symptoms such as fever, cough, and chest pain, and can be diagnosed through culture of respiratory specimens or tissue biopsy. The bacteria can be identified using microscopy, PCR, and molecular techniques. Treatment involves the use of antibiotics, such as sulfonamides, trimethoprim-sulfamethoxazole, and amikacin, which target bacterial cell wall synthesis and protein synthesis.

**Why Each Wrong Option is Incorrect**

**Option A:** Nocardia species are typically aerobic. This statement is correct, as Nocardia species are aerobic and require oxygen for growth.

**Option B:** Nocardia infections are typically seen in immunocompetent individuals. This statement is incorrect, as Nocardia infections primarily affect immunocompromised individuals.

**Option C:** Nocardia species can be identified using acid-fast staining. This statement is correct, as Nocardia species can be identified using acid-fast staining, which highlights their characteristic weakly acidic cell wall.

**Option D:** Nocardia species are typically gram-negative. This statement is incorrect, as Nocardia species are gram-positive.

**Clinical Pearl / High-Yield Fact**

Nocardia infections can be prevented by avoiding exposure to contaminated soil and water, and by maintaining good hygiene practices. Additionally, individuals with immunocompromised conditions should be aware of their increased risk and seek medical attention promptly if symptoms develop.

**Correct Answer: B. Nocardia infections primarily affect immunocompromised individuals.**