Role of polymorphonuclear neutrophils in the clearance of Enterococcus faecalis derived from saliva and infected root canals

Objectives

The goal of this study was to measure (1) the ability of polymorphonuclear neutrophil leukocytes (PMNs) to kill oral Enterococcus faecalis strains, (2) up-regulation of inflammatory mediators by PMNs in interaction with E. faecalis, and (3) the ability of E. faecalis to cause inflammation in mouse muscle tissue.

Methods

Fifteen endodontic and nine saliva strains of E. faecalis were isolated and identified by specific 16S ribosomal RNA (16S rRNA) primers. The bacteria were grown in BHI broth and incubated with mouse PMN in appropriate media to determine the ability of the PMNs to kill the bacteria. In other experiments up-regulation of interleukin (IL)-1α, tumor necrosis factor α (TNF-α), matrix metalloproteinase-8 (MMP-8), and cyclooxygenase (COX)-2 messenger RNA in the PMNs was measured after exposure of the leukocytes to the bacteria using real-time polymerase chain reaction. Finally, the inflammatory potential of and PMN response to E. faecalis suspension in mouse muscle tissue was examined from histological sections using hematoxylin-eosin staining and immunostaining.

Results

Murine PMNs killed about 80% of the E. faecalis cells in 1 hour, irrespective of the source of isolation of the strains. Quantitative PCR results showed that IL-1α, TNF-α, MMP-8, and COX-2 messenger RNA were markedly up-regulated in E. faecalis-stimulated PMNs or in E. faecalis-invaded muscular tissues. MMP-8 messenger RNA level was positively related to COX-2 messenger RNA level. Histological evaluation and immunostaining disclosed that all E. faecalis strains could recruit PMNs to the local infectious sites and cause abscess formation.

Conclusion

E. faecalis strains from saliva and infected root canals have the potential to recruit PMNs in the infectious sites leading to inflammation via up-regulation of PMN IL-1α, TNF-α, MMP-8, and COX-2. PMNs can play an important role in killing of E. faecalis.