A polyether antibiotic; active against a variety of Gram-positive bacteria, including various strains of S. aureus and Streptococcus, as well as one strain of S. pneumoniae (MICs = 4, 4, and 2 μg/ml); active against coccidia in vitro but not in vivo in chicks at 200 μg/g in the diet; acts as an ionophore in lipid bilayer membranes and is selective for potassium ions; induces histamine release from rodent mast cells and human basophils in vitro in a calcium-dependent manner