Cytotoxicity in bacterial cultures: interaction and cell-specificity, possible factors in periodontal disease.

Cytotoxicity in culture media of various growing bacterial strains was estimated by Cr-51 release of labelled target-cells. Interaction studies were made by adding each of the different UV-killed bacteria to the medium with viable bacteria. The reference oral bacterial strains were: Actinobacillus actinomycetemcomitans Y4, Porphyromonas gingivalis, Fusobacterium nucleatum and Streptococcus mitis, which were compared with the reference bacteria Staphylococcus aureus 209 and Staphylococcus epidermidis. The target cells were: gingival fibroblasts (GF), periodontal membrane fibroblasts (PMF), pulpal fibroblasts (PF), HeLa-cells (HeLa), and lymphoid neoplasm cells (LN). Synergistic, as well as antagonistic, effects on target cells were observed. The cytotoxicity of A. actinomycetemcomitans in presence of P. gingivalis is neutralized while in presence of S. aureus it was increased. Bacterial interactions with F. nucleatum and P. gingivalis cytotoxicity were observed. The cytotoxicity of F. nucleatum was increased when cultured together with A. actinomycetemcomitans. Each cell type reacted differently to the toxicity of the supernatant of growth medium in which the same bacterial strain had been cultivated, which indicates cell specificity of the toxins.