Effects of Bacteroides gingivalis culture products on human polymorphonuclear leucocyte morphology

This study aimed to determine whether leucocytes exposed to Bacteroides gingivalis culture supernatant exhibited consistent morphological changes and whether measurement of such changes could provide a simple screening assay for bacterial products with potential biological activity. Glass-adherent polymorphonuclear leucocytes were obtained from clotted blood preparations and from blood after purification by centrifugation through Ficoll-Hypaque. These were then incubated in Hanks' balanced salt solution, a sterile liquid medium (BM) and B. gingivalis (W83) culture supernatant. Polymorphonuclear leucocytes were classified by their shape into small non-polar (less than 18 microns diameter), large non-polar (greater than or equal to 18 microns diameter), bipolar and hyperpolar types. Treatment with B. gingivalis culture supernatant consistently increased large non-polar cells by 150% to over 300% (p less than 0.01), when compared with polymorphonuclear leucocytes incubated with the sterile liquid medium (control). This change was accompanied by smaller decreases in small non-polar, bipolar and hyperpolar cells, these being significant for bipolar cells in clot preparations (p less than 0.01) and small non-polar cells after Ficoll-Hypaque isolation (p less than 0.01). Neither the liquid medium nor the B. gingivalis culture supernatant was toxic to the cells as indicated by trypan blue exclusion tests. Lipopolysaccharide and short-chain fatty acids were not responsible for the changes in polymorphonuclear leucocyte shape. However, the activity of the culture supernatant was destroyed by heating at 80 degrees C for 30 min, indicating that proteolytic enzymes may have been involved.