Endogenous/exogenous epinephrine supply iron to E. faecalis from transferrin

Enterococcus faecalis has been implicated in the pathogenesis of several infectious diseases including endodontic failure (Portenier et al., Endo Topics 6,135-159, 2003). Oral organisms vary in their responsiveness to the stress hormone epinephrine (Roberts et al., Oral Microbiol & Immunol 17, 296-303, 2002) which can act as an endogenous siderophore and promote the growth of E. coli by releasing bound iron from transferrin (Tf; Freestone et al., J Bacter 182, 6091-8, 2000). Iron acquisition is a fundamental virulence determinant for several oral pathogens and tissue epinephrine levels may increase from endogenous sources (stress responses) or exogenously by the administration of local anaesthetics. Objective: To investigate whether endogenous or local anaesthetic derived-epinephrine facilitate the supply of transferrin-bound iron to E. faecalis. Methods: E. faecalis (ATCC 29212) was grown to turbidity anaerobically (37°C) in mycoplasma broth and used to inoculate a minimal medium (SAPI: 30% serum) containing 55Fe-transferrin ± 100µM epinephrine or lignocaine (amount equivalent to 100µM epinephrine). After 7 days culture (anaerobic, 37°C), iron uptake from transferrin was determined by scintillation counting of washed bacteria normalised for growth (OD_600nm). Triplicate assays were performed. Results: Both forms of epinephrine increased the acquisition of transferrin-bound 55Fe and increased the 7 day growth of E. faecalis. The effects of epinephrine on uptake of 55Fe, expressed as the percent change from non-supplemented cultures, were epinephrine (+525%) and lignocaine (+35%). The effects of epinephrine on growth as the percent change from non-supplemented cultures, were epinephrine (+10.2%) and lignocaine (+0.2%). Conclusion: Enterococcus faecalis is capable of using endogenous epinephrine and local anaesthetic derived epinephrine to acquire transferrin-bound iron in-vitro. Enterococcus faecalis may use epinephrine to acquire sequestrated iron for growth and virulence expression which may be important in the failure of endodontic treatment.

Study supported by British Endodontic Society.