Effect of microbial interactions on bacterial colonization of epithelial cells

Objective: Actinobacillus actinomycetemcomitans (Aa) is considered to be a key pathogen for periodontal destruction. The adhesion of this pathogen to epithelial cells is a first important step in this mucosal infection. Although a lot of information is available regarding this process, the effect of beneficial bacteria on this process is largely unknown. This project aimed to screen 7 presumed benefical bacterial species (Actinomyces naeslundi, Streptococcus cristatus, Streptococcus sanguinis, Streptococcus mitis BMS, Streptococcus salivarius TOVE-R, Fusobacterium nucleatum mut113 and Haemophilus influenzae) on their ability to interfere with the adhesion of Aa to epithelial cells. Methods: Confluent epithelial monolayers were inoculated following 3 different infection protocols: mixed infection (a mixture of a beneficial strain and Aa was left to adhere for 2 hours), pre-infection (the epithelial cells were infected for 2 hours with a beneficial strain and subsequently for another 2 hours with Aa) and post-infection (the epithelial cells were infected for 2 hours with Aa and subsequently for another 2 hours with a beneficial strain). Mono-infections of Pg or of the beneficial strains were used as controls. The epithelial colonization resulting from these interactions was analyzed by microbial culturing. Results: The most pronounced inhibition of the attachment of Aa was seen for the streptococcal strains. Of all tested strains, S. sanguinis had the most pronounced effect on Aa colonization. The interactions between Aa and the presumed beneficial strains also resulted in changes of colonization behavior of the beneficial strains. Conclusion: The microbial interactions between Aa and the presumed beneficial strains are species specific and can affect the colonization of epithelial cells. New analyzing techniques and in vitro models, which allow longer interaction times, are needed to further explore these microbial interactions during bacterial adhesion to epithelial cells. (Supported by NIDCR grant 1 R21 DE015360-01)