Streptomyces noursei

from The Collaborative International Dictionary of English v.0.48

nystatin \nystatin\ n. [From NY state + -in, due to its
   discovery in New York State.]
   An antifungal antibiotic, extracted from fermentation broths
   of the soil actinomycete {Streptomyces noursei} and other
   actinomycetes; called also {fungicidin}. It is a polyene
   macrolide antibiotic, and consists of several related
   components. Component nystatin A1 has formula {C47H75NO17}.
   [WordNet 1.5]