August 28, 2007
When describing oral bacteria, dentists often mention “commensals.” The term refers to the “good” bacteria that tend to be plentiful in the mouths of people with healthy gums and which often are lower in number among those with periodontal disease. As well established as this paradigm is the dentistry, much remains to be learned about how commensals keep the “bad,” or pathogenic, bacteria from proliferating and infecting the gums. In the July issue of the Journal of Dental Research, NIDCR grantees and colleagues take a close look at this issue. Using cultured epithelial cells, they evaluated the ability of seven presumed commensals to interfere, exclude, or displace the oral pathogen Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans. A. actinomycetemcomitans is strongly associated with juvenile periodontal disease. The scientists determined that three presumed commensals - Streptococcus sanguinis, Streptococcus mitis, and Streptococcus salivarius - had prominent inhibitory effects on the colonization and/or recovery of A. actinomycetemcomitans. Interestingly, commensals Actinomyces naeslundii and Haemophilus parainfluenzae facilitated the colonization of A. actinomycetemcomitans. But as the researchers noted, “The colonization of the test strains was also affected by the pathogen, indicating that these are two-way interactions, influencing the colonization of both pathogen and test strains.” According to the authors, this study is the first to be published that describes in vitro interference of an oral pathogen’s colonization of epithelial cells.