When describing oral bacteria, dentists often mention “commensals.” The term refers to the “good” bacteria that is plentiful in mouths with healthy gums and often is lower in number among those with periodontal disease. Although a well-established paradigm in dentistry, much remains to be learned about how commensals keep the “bad,” or pathogenic, bacteria from proliferating and infecting the gums. In the Journal of Dental Research (July 2007), National Institute of Dental and Craniofacial Research grantees and colleagues look at this issue. Using cultured epithelial cells, they evaluated the ability of 7 presumed commensals to interfere, exclude, or displace the oral pathogen Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans, which is strongly associated with juvenile periodontal disease. The scientists determined that 3 presumed commensals, Streptococcus sanguinis, Streptococcus mitis, and Streptococcus salivarius, had prominent inhibitory effects on the colonization and/or recovery of A. actinomycetemcomitans. Interestingly, the 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.
(Source: NIDCR, Science News in Brief, August 28, 2007)
