Macrolide antibiotics that target fungi, including amphotericin B and nystatin, amongst others, are some of the most effective therapeutics against potentially life-threatening fungal infections in humans
[23]. In 1950, nystatin was the first polyene macrolide antifungal compound to be discovered by Rachel Fuller Brown and Elizabeth Lee Haze. It was also the first widely available and effective antifungal treatment. Brown and Haze cultured
Streptomyces noursei from soil found near a dairy farm in Fauquier County, Virginia, and determined its antifungal properties by screening it against
C. albicans and
C. neoformans. Nystatin was then purified and characterized from the
Streptomyces noursei cultures
[24][25]. This work led to the continuation of mycological studies and the subsequent discovery of amphotericin B (AmB) in 1955 at the E.R. Squibb Institute
[25][26]. Amphotericin B, which is the current “gold standard” of treatment for fungal infections, was isolated from cultures of
Streptomyces nodosus found in soil near the Orinoco River of Venezuela and has been shown to have broad antifungal activity, as well as antiparasitic activity
[26]. Two additional antifungal compounds were discovered in 1955: natamycin (previously called pimaricin) and filipin
[27][28]. Natamycin was isolated from a culture of
Streptomyces natalensis found in soil from Natal, South Africa
[27]. Filipin was named after its place of discovery, the Philippines, where it was isolated from
Streptomyces filipinesis [28]. Cruentaren A and B were identified more recently and were isolated from
Byssovorax cruenta. Cruentaren A is most commonly used as an antifungal treatment, as cruentaren B displays a lack of antifungal activity
[29][30].
2.5. Immunosuppressants
The macrolide immunosuppressants represent a more recently discovered class of drugs that are used to prevent organ transplant rejection and treat inflammatory skin diseases
[31]. Tacrolimus is an immunosuppressant that was discovered in 1984 in
Streptomyces tsukabaensis cultures found from soil near Tsukuba, Japan
[32][33]. It has been used to prevent kidney, liver, and bone marrow rejection in transplant patients
[33][34][35]. A topical formulation of tacrolimus is the first non-glucocorticoid shown to be effective at treating atopic dermatitis
[34]. Pimecrolimus is an ascomycin derivative that was developed specifically to treat inflammatory skin conditions, including psoriasis and atopic dermatitis
[36][37]. Rapamycin, known by the common name sirolimus, was isolated from the actinomycete
Streptomyces hygroscopicus from soil found on Easter Island, where it was first determined to display antifungal properties
[38][39][40][41][42]. It was later found to display immunosuppressive properties, and has been developed for the prevention of renal, pancreatic islet cell, liver, and heart transplant rejection
[38][43].