Associations between microbial species in subgingival plaque samples

Samples of subgingival plaque were taken from 275 active and inactive sites in 35 subjects with destructive periodontal diseases. The predominant cultivable microbiota was determined in each of the samples by characterizing 50 randomly selected isolates recovered on anaerobically incubated Trypticase soy agar supplemented with 5% sheep blood. Microbial associations between species were determined by computing the odds ratio of a site being infected by a “target” species in the presence of an “effector” species. Data are presented for 22 numerically dominant “effector” species and 8 “target” species which consisted of suspected periodontal pathogens. These included Actinobacillus actinomycetemcomitans, Bacteroides forsythus, Bacteroides gingivalis, Bacteroides intermedicus, Bacteroides melaninogenicus, Peptostreptococcus micros, Streptococcus intermedius and Wolinella recta. Positive associations were considered to be relationships in which the odds ratio of detecting a “target” species was >2:1 in the presence of the “effector” species, while negative associations were defined as those in which the odds ratio of detecting the “target” species was < 0.5:1 in the presence of the “effector” species. In general, species of streptococci, an unnamed Actinomyces sp. and Propionibacterium acnes showed a negative association with the 8 suspected pathogens, while many Gram‐negative species tended to show a positive association with these suspected pathogens. There appeared to be specificity in the associations observed. For example, S. intermedius was positively associated with Streptococcus mitis and Streptococcus sanguis I , but negatively associated with Bacteroides forsythus. In contrast, W. recta was negatively associated with S. mitis and Streptococcus sanguis I , but positively associated with Bacteroides forsythus. S. sanguis II, Streptococcus uberis, P. acnes, Capnocytophaga ochracea and an unnamed Actinomyces sp. showed negative associations with 4 of the suspected periodontal pathogens, while B. gingivalis, Fusobacterium nucleatum and the Eubacterium sp. showed only positive or “neutral” associations with the “target” species. Data from this and other investigations suggest that microbial associations might play an important role in controlling the composition of subgingival plaque and, thus, be a major determinant of health or destructive periodontal diseases.