Background: We previously demonstrated an association between interleukin-6 (IL-6) polymorphisms and the detection of periodontopathogenic bacteria in aggressive and chronic periodontitis on a patient basis (pooled samples). The aim of this study is to comprehensively analyze the relative contribution of IL-6 genetic factors and local (tooth and site) factors on the detection of Aggregatibacter actinomycetemcomitans (previously Actinobacillus actinomycetemcomitans) and Porphyromonas gingivalis in patients with chronic periodontitis.
Methods: Forty patients diagnosed with severe chronic periodontitis had subgingival samples harvested from four sites (the deepest probing depths in each quadrant). All subjects had a blood sample taken to genotype the single nucleotide polymorphism at position -174 in the IL-6 gene promoter. Nested polymerase chain reaction analysis was performed on subgingival plaque samples for the detection of A. actinomycetemcomitans and P. gingivalis in each of the 160 sampled sites. The association between IL-6 -174 genotypes and bacterial detection was investigated with multilevel analysis accounting for the clustering of multiple sites analyzed within patients.
Results: Respectively 60%, 62%, and 40% of subjects had A. actinomycetemcomitans, P. gingivalis, and both bacteria concomitantly detected in ≥1 site. The multilevel analysis confirmed that, among all site and subject factors, IL-6 -174 G homozygosity showed the strongest association with the presence of A. actinomycetemcomitans in all subjects and in the subgroup of whites only. No associations were detected for P. gingivalis.
Conclusion: This study provides further confirmatory evidence that the detection of A. actinomycetemcomitans is associated with IL-6 genetic factors in chronic periodontitis cases.