Differential morphological changes in human polymorphonuclear leucocytes induced by culture products of Porphyromonas (Bacteroides) gingivalis W50 and its colonial variants with reduced virulence

The colonial variants of W50, derived after growth in a chemostat and previously designated W50/BP1, W50/BR1 and W50/BE1, produced black-, brown- and beige-pigmented colonies, respectively, and showed reductions in mouse virulence and proteolytic activity correlating with their reduced pigmentation. Incubation of glass-adherent polymorphonuclear leucocytes with culture supernatants from the virulent, highly proteolytic, black-pigmented strain produced significant changes in morphology when compared with changes among sterile bacterial growth medium treated, control polymorphonuclear leucocytes. Large, non-polar cells (⩾ 18 μm dia) increased by 130% ( p < 0.01) while polarized and small non-polar cells (< 18 μm dia) decreased by 48 and 30% ( p < 0.05), respectively. Changes in percentages of the different morphological forms of polymorphonuclear leucocyte after exposure to the culture supernatant from the less virulent W50/BR1 variant showed similar, though less marked trends, while the avirulent W50/BE1 variant failed to produce significant changes in any morphological category. The specific activities of trypsin-like enzyme in the culture supernatants of the different variants were greater in black-pigmented than brown-pigmented and least in the beige-pigmented variant, thus correlating with the morphological changes in polymorphonuclear leucocytes. Morphological changes similar to those seen with culture supernatants from black-pigmented strains were reproduced by exposure of polymorphonuclear leucocytes to commercially available trypsin type II and prior heat treatment of these culture supernatants abolished the shape changes in polymorphonuclear leucocytes. Thus a bacterial, trypsin-like enzyme may play a role in the morphological changes observed.