The Effect of Gram-positive or -negative Bacteria Homogenates on Periodontal Tissue of Immunized Rats

Abstract

 Purpose: Gram-negative bacteria is a periodontal pathogen. Although the proportion of gram-negative bacteria increases markedly in gingival microflora with increasing severity of periodontitis, gram-positive bacteria is dominant in healthy gingival sulcus. Therefore, it is important to investigate the influence of gram-positive bacteria on the onset of periodontitis. In our previous study, we used heat-treated and sonicated Staphylococcus aureus as gram-positive bacteria, or Aggregatibacter actinomycetemcomitans as gram-negative bacteria, and both bacteria induced strong periodontal destruction in rats, so it was not clear which bacteria has a stronger influence in periodontal destruction. In the present study, we used a lower concentration of bacterial suspension than in the previous study, and histopathologically examined the influences of both bacteria homogenates on periodontal tissue.
 Methods: Rats previously immunized with heat-treated and sonicated S. aureus or A. actinomycetemcomitans were used as immunized groups. The non-immunized groups intraperitoneally received only sterile phosphate-buffered saline. In each animal, 12.5 μg/μl S. aureus or A. actinomycetemcomitans suspension was applied topically to the palatal gingival sulcus of first molars every 24 hours for 10 days. The first molar regions were resected and observed histopathologically. The control group did not receive the topical application.
 Results: The loss of attachment and decreases in alveolar bone level in the A. actinomycetemcomitans immunized group were significantly greater than in the control group. However, a statistically significant difference was not observed in the S. aureus immunized group or the A. actinomycetemcomitans non-immunized group. C1qB, which indicates the existence of immune complexes, was observed in the junctional epithelium in the A. actinomycetemcomitans immunized groups.
 Conclusion: Our results suggest that A. actinomycetemcomitans as gram-negative bacteria has a stronger influence on periodontal destruction than S. aureus as gram-positive bacteria. The presence of C1qB suggests that the formation of immune complexes is involved in periodontal destruction.