Objectives: The purpose of this study was to demonstrate the role of microbial coaggregation on the killing ability of polymorphonuclear leukocytes (PMNs).
Methods: A coaggregated bacterial pairs (S. gordonii and P. melaninogenicus); which were previously isolated from an endodontic abscess, and spontaneously occurring coaggregation-defective mutants of P. melaninogenicus were tested with human PMNs using bacterial killing assay and fluorescent microscopic observation. In bacterial killing assay, bacteria in coaggregated or non-aggregated form were mixed with the PMNs. The percent reduction of bacterial colony forming units from both groups was compared. The difference between groups was analyzed by one way ANOVA and Post Hoc test using SPSS. The fluorescent microscopic observation was determined by staining bacteria in both forms with a green nucleic acid stain before being added to the reaction mixtures containing the PMNs. Propidium iodide was then added to stain dead cells before being observed with a fluorescence microscope.
Results: Under the condition tested in this study, coaggregation between the bacterial pairs caused significantly greater bacterial killing by the PMNs (p<0.001) and seemed to promote more PMN accumulation and cytolysis than the counterparts containing coaggregation-defective mutants.
Conclusions: Coaggregated bacteria were better killed by PMNs but seemed to promote the secretion and local death of the PMNs which might lead to abscess formation.
This study was supported by the Royal Golden Jubilee Ph.D. program of the Thailand Research Fund.