Which of the following is an antifungal agent?

Amphotericin B is classified as an antifungal agent due to its mechanism of action that targets fungal cell membranes. It binds to ergosterol, a key component of fungal membranes, creating pores that lead to cell death. This makes it effective in treating a variety of serious fungal infections, such as cryptococcal meningitis and fungal infections in immunocompromised patients.

The other agents listed do not have antifungal properties; they serve different therapeutic purposes. Rifampin is primarily used as an antibiotic, particularly in the treatment of tuberculosis. Streptomycin is also an antibiotic, often used against certain bacterial infections, and Ethambutol is another antituberculosis medication that works by inhibiting the synthesis of the bacterial cell wall. Therefore, Amphotericin B stands out as the only antifungal agent on the list.