Selected low-cohesion variants of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus lack distinct antigens recognized by human antibodies.

Actinobacillus actinomycetemcomitans OMZ 346 A and Haemophilus aphrophilus OMZ 384 A, isolated on a synthetic selective and differentiating agar, show the highly cohesive and wall adherent growth in liquid medium which is typical for all primary oral isolates of these species. From each of them a low cohesion variant, OMZ 346 F and OMZ 384 F, respectively, was obtained by selection for cells growing in suspension. Screening of Western blots of these four strains with several human sera revealed the loss of a 4000 Mr antigen in both F strains. Human antibodies bound to the 4000 Mr band material on preparative Western blots of the A strains were eluted with 4 M magnesium chloride. These antibodies showed no cross-reaction between the 4000 Mr material of the two closely related species.