Bactericidal effect of pooled human serum on Bacteroides melaninogenicus, Bacteroides asaccharolyticus and Actinobacillus actinomycetemcomitans.

Bacteria belonging to the species B. melaninogenicus ss. melaninogenicus (two strains), B. melaninogenicus ss. intermedius (five strains), B. asaccharolyticus (seven strains), and Actinobacillus actinomycetemcomitans (four strains) were tested under anaerobic conditions for their sensitivity to the bactericidal effect of pooled human serum. The A. actinomycetemcomitans strains were not killed to any extent by the serum. Both B. melaninogenicus ss. melaninogenicus strains were killed by serum. The sensitivity to serum among the strains of B. asaccharolyticus and B. melaninogenicus ss. intermedius was diverse. There was no correlation between the sensitivity to serum among the strains and the levels of specific antibodies in the serum. The bactericidal activity of serum was only effective if the complement system was present in serum. All strains initiated activation of complement and binding of a C3 component to the cell surface both in normal and MgEGTA chelated serum. The possible role of serum bactericidal activity in the pathogenesis of oral infections is unclear.