2004 Spring Scientific Meeting of the British Endodontic Society

Abstract

Co‐aggregation studies on bacteria from infected root canalsAim Co‐aggregation phenomena may play a crucial role in root canal colonization and subsequent infection, and may be an important aspect of the selection process taking place. The aims were to determine intracanal and intercanal co‐aggregation partners in bacterial strains isolated from infected root canal systems.Methodology Bacterial strains isolated from the root canals of four intact teeth, and one strain of Fusobacterium nucleatum from a separate tooth were selected for the study. The isolates were grown in static culture at 37 °C in brain heart infusion broth. The cells were harvested by centrifugation and prepared for the co‐aggregation study in an appropriate buffer. Aliquots (100 µL) of each pair of isolates (all combinations) were placed in a durham tube, mixed and left to settle. A visual co‐aggregation assay was performed after 1–2 h after pairing and again 6–7 h later. Co‐aggregation was judged by a predetermined 5‐point visual assessment scale, which showed good reproducibility.Results Co‐aggregation results were identical at the different time points. Physical interaction between bacterial cells within a genus and between different genera was surprisingly infrequent; where it manifested in auto‐aggregation (within strain) or co‐aggregation, it was found to be species‐ and strain‐specific. Actinomyces viscosus, Rothia dentocariosa, Streptomyces scabei, Neiserria mucosa and two unidentified strains displayed auto‐aggregation. Intrageneric and intergeneric co‐aggregation was observed both between strains from the same tooth and those from different teeth. Sometimes, strains that showed no intracanal co‐aggregation were identified as co‐aggregation partners with strains from different teeth. Intrageneric co‐aggregation occurred between Streptococcus species, and intergeneric co‐aggregation involved Abiotrophia adiacens, A. naeslundii, Pediococcus urinaeequii, R. dentocariosa, S. scabei, Streptococcus gordonii and S. mitis. The F. nucleatum strain tested for co‐aggregation did not auto‐aggregate or co‐aggregate with any of the isolates it was paired with.Conclusions This study showed that co‐aggregation is species‐ and strain‐dependent, and was surprisingly infrequent among the various pairings. The renowned associations between root canal isolates may be dominated by interactions other than physical, such as nutritional and physiological dependence.