An antibiotic (trade name Erythrocin or E-Mycin or Ethril or Ilosone or Pediamycin) obtained from the actinomycete Streptomyces erythreus; effective against many Gram-positive bacteria and some Gram-negative. Synonyms: Erythrocin, erythromycin, Ethril, Ilosone, Pediamycin.