Erythromycin 2'-propionate is a macrolide antibiotic and an esterified form of erythromycin .1It is active againstS. aureuswhen used at a concentration of 1 μg/ml. Erythromycin 2'-propionate (1 mM) inhibits protein synthesis in a cell-free assay. 1.Tardrew, P.L., Mao, J.C.H., and Kenney, D.Antibacterial activity of 2'-esters of erythromycinAppl. Microbiol.18(2)159-165(1969)