Release of toxic microvesicles by Actinobacillus actinomycetemcomitans

Oral isolates of Actinobacillus actinomycetemcomitans (strain Y4) release spherical microvesicles in large numbers during normal growth. The biological activities of these products were studied, and it was estimated that approximately 1/10 of their dry weight was made up of heat- and proteolysis-resistant endotoxin. The chicken embryo lethality and bone-resorbing activity of the microvesicles were heat stable but proteolysis sensitive. Other laboratories have reported the presence of a heat- and proteolysis-sensitive leukotoxin in similar preparations. Accordingly, the microvesicles released by strain Y4 may contain, in addition to endotoxin, several potent substances which are highly toxic and active in bone resorption, and these may be significant factors in the pathogenesis of periodontal diseases.