Required for persistent infection. Forms both homodimers and heterodimers with EsxA. Homodimerization is calcium-dependent. Secreted during infection via the ESAT-6 secretion system (Ess) / type VII secretion system (T7SS). Negatively regulated by EsaB. Deletion mutants display only a small defect in acute infection, but remarkably are unable to promote persistent abscesses during animal infection. Belongs to the EsxC family.