Microtubules are associated with intracellular movement and spread of the periodontopathogen Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans SUNY 365, the invasion prototype strai n, enters epithelial cells by an actin-dependent mechanism, escapes from th e host cell vacuole, and spreads intracellularly and to adjacent epithelial cells via intercellular protrusions. Internalized organisms also egress fr om host cells into the assay medium,ia protrusions that are associated with just a single epithelial cell. Here we demonstrate that agents which inhib it microtubule polymerization (e.g., colchicine) and those which stabilize polymerized microtubules (e.g., taxol) both increase markedly the number of intracellular A. actinomycetemcomitans organisms. Furthermore, bath colchi cine and taxol prevented the egression of A. actinomycetemcomitans from hos t cells into the assay medium, Immunofluorescence microscopy revealed that protrusions that mediate the bacterial: spread contain microtubules, A. act inomycetemcomitans SUNY 465 and 652, strains that are both invasive and egr essive, interacted specifically with the plus ends (growing ends) of the fi laments of microtubule asters in a KB cell extract. By contrast, neither A. actinomycetemcomitans 523, a strain that is invasive but not egessive, nor Haemophilus aphrophilus a noninvasive oral bacterium with characteristics similar to those of A. actinomycetemcomitans bound to microtubules, Togethe r these data suggest that microtubules function in the spread and movement of. A. actinomycetemcomitans and provide the first evidence that host cell dispersion of an invasive bacterium may involve the usurption of host cell microtubules.