Application Erythromycin ethyl succinate is used to study erythromycin-resistant Streptococcus pyogenes and Streptococcus pneumoniae1. It has been used to study down-regulation of motilin receptors on rabbit colon myocytes2 and lethal mutations in outer membrane genes omsA and firA in Salmonella typhimurium3. Biochem/physiol Actions Erythromycin ethyl succinate inhibits protein synthesis (elongation) at the level of transpeptidation (aminoacyl translocation A-site to P-site). Erythromycin inhibits protein synthesis (elongation) at the level of transpeptidation (aminoacyl translocation A-site to P-site) by binding to the 50s subunit of the bacterial 70s rRNA complex.