Electron microscopic study of the interaction of oral microorganisms with polymorphonuclear leukocytes

A variety of Gram-positive plaque bacteria can trigger lysosomal enzyme release from rabbit polymorphonuclear leukocytes (PMNs) in vitro. This electron microscopic study was undertaken to assess the correlation between phagocytic activity by PMNs and lysosome release to Streptococcus mutons 6715, Streptococcus sanguis G9B, and Actinomyces viscosus T14. PMN phagocytic activity was quantitated by determining the percentage of cells showing evidence of phagocytosis (phagocytic index) and the number of bacteria within the PMNs (avidity index). High phagocytic activity was accompanied by vigorous PMN lysosomal enzyme release. On the other hand, when PMNs exhibited low phagocytic activity lysosomal enzyme release was minimal. For example, Streptococcus mutans grown in brain-heart infusion broth did not induce significant lysosome release or demonstrable phagocytic activity by PMNs. In contrast, Strep. mutans grown in BHI containing sucrose or pre-incubated with anti-Strep. mutans antibodies acted as potent triggers of lysosome release and PMN phagocytosis. Our results indicate that various species of oral Gram-positive bacteria trigger different responses from PMNs and that phagocytic activity of PMNs correlates well with the ability of these microorganisms to stimulate lysosomal enzyme release.