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: E-Mycin, Erythrocin, erythromycin, Ilosone, Pediamycin.