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The extracellular vesicles (ECV) and extracellular protein (EP) fractions of Bacteroides gingivalis W50 showed haemagglutinating (HA) activity towards sheep erythrocytes. Similar fractions from the nonpathogenic strain W50/BE1 did not haemagglutinate. W50 ECV HA activity was not inhibited by various glycosidase, phospholipase or protease pretreatments, sugars or amino acids, including arginine or lysine. The haemagglutinating activity of ECV was associated only with the extracellular vesicle membrane. The EP and ECV of both strains displayed haemolytic activity. This activity was apparently depressed in the presence of 10 mM dithiothreitol (DTT). All EP and ECV fractions degraded certain structural sheep erythrocyte membrane proteins. The greatest activity was displayed by W50 ECV and W50/BE1 EP and was enhanced by DTT. In the presence of DTT, the ECV of both strains degraded purified human haemoglobin but this activity was greatly reduced in its absence.

The effects of B. gingivalis W50 extracellular vesicles (ECV) on neutrophil chemotaxis and viability were assessed and compared with those of whole cells and the extracellular non-dialysable soluble protein (EP) fraction. None of the fractions tested, including soluble fractions derived from cells and ECV by sonication, induced neutrophil chemotaxis. Only ECV and cells inhibited f-MLP-stimulated chemotaxis. ECV and cells were cytotoxic towards neutrophils. The cytotoxic response was time dependent. The soluble EP fraction did not influence cell viability.

Forty strains of bacteria which may be isolated from subgingival plaque were tested for their in vitro susceptibility to several amine fluorides and a commercial formulation (Elmex gel) containing these compounds. The amine fluorides were active against a wide range of plaque bacteria with gram-positive strains tending to be more sensitive than gram-negatives. The minimum inhibitory concentrations ranged from 45 to 1440 micrograms/ml with approximately half of the strains being inhibited at a concentration of 130 micrograms/ml of amine fluoride. The Elmex gel had a bactericidal effect on all of the strains tested and exhibited a rapid killing action at high dilutions. These in vitro findings suggest that amine fluorides may be useful in the treatment or prophylaxis of plaque-related diseases.

The distribution of trypsin-like enzyme activity was studied in 48- and 72-h batch cultures of Bacteroides gingivalis W50 and an avirulent variant (W50/BE1) of the parent strain. Activity was measured at pH 7.4 in cells, the extracellular vesicle (ECV) and soluble extracellular protein (EP) fractions recovered by ammonium sulphate precipitation from spent growth medium. Both organisms produced cell surface and extracellular vesicles, but whilst strain W50 produced more ECV, W50/BE1 yielded more of the EP fraction by weight. Whole cultures of W50 displayed a three-fold greater trypsin activity than those of W50/BE1. However, 90% of the total enzyme activity of W50 cultures was associated with the particulate fraction (cells and ECV totalled), whereas this fraction accounted for only 10-30% of the total for W50/BE1. Unlike W50/BE1, the specific activities of W50 cells and ECV rose in 72-h cultures. Conversely, cultures of W50/BE1 displayed an increase in the yield and specific activity of the EP fraction.

Glycylprolyl dipeptidase activity was measured in cells, extracellular vesicles (ECV) and the soluble extracellular protein fraction (EP) of batch cultures of strains W50 and W50/BEI. Total culture enzyme activity of W50 dropped with age whilst that of W50/BEI remained constant. Activity was highest in the cellular fraction, greater for W50/BEI than W50 and rose with culture age. Both strains showed similar ECV activities but these declined with culture age. The EP glycylprolyl dipeptidase activity of W50/BEI in older cultures rose to a level 13-fold greater than W50. The majority of extracellular activity was represented by the ECV for strain W50 but by EP for W50/BEI. Variable but incomplete attenuation of activity was achieved by dithiothreitol. ECV and EP activities were associated with a high molecular mass fraction, but a smaller fraction (molecular mass 30,000) was detected in W50/BEI EP.