Peptostreptococcus micros and
Streptococcus constellatus are organisms associated with periodontal abscesses (Dahlen, 2002). Periodontal bacteria vary in their
in vitro growth responses to the stress hormone norepinephrine (Roberts
et al, 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, 2000). Iron acquisition is a fundamental virulence determinant for periodontal pathogens and may contribute to their enhanced survival and therefore abscess formation. The periodontal tissues form an iron-limited environment (Holt
et al, 1999) due to the presence of various iron-binding proteins such as Tf.
Objective: To investigate whether norepinephrine facilitates the supply of Tf-bound iron to bacteria associated with periodontal abscesses.
Methods: Initial cultures of each organism were established (to turbidity) anaerobically (37°C) in mycoplasma broth. Organisms were inoculated into a minimal medium (SAPI: 30% serum) containing 55Fe-Tf and grown anaerobically (37°C) ± 50μM norepinephrine or ± 50μM ferric nitrate (Fe: +ve control). After 7-days, iron acquisition from transferrin was determined by scintillation counting of washed bacteria normalised for growth by optical density readings (600nm). Triplicate assays for
P. micros (ATCC 33270) and
S. constellatus (ATCC 27823) were performed 3-times.
Results: Norepinephrine increased the acquisition of Tf-bound 55Fe for both organisms investigated. The effect of norepinephrine (Fe) on uptake of Tf-bound 55Fe, expressed as the percent change from non-supplemented cultures, were: ATCC 33270, +327% (+371%) and ATCC 27823, +30% (+484%). Changes in 55Fe uptake were also associated with changes in growth: ATCC 33270, +14% (+4%) and ATCC 27823, +24% (+13%).
Conclusion: Abscess forming organisms are capable of using norepinephrine to acquire transferrin-bound iron
in-vitro. Further studies are needed to evaluate whether this siderophore-like property of norepinephrine contributes mechanistically to the process of abscess formation.
Supported by the British Society of Periodontology