Possible potentiation of toxins from Prevotella intermedia, Prevotella nigrescens, and Porphyromonas gingivalis by cotinine

Background: Smoking is a recognized risk factor for the initiation and prog ression of periodontitis. However, the mechanism by which smoking induces i ts negative effects on the periodontium is not clear. This study aimed to t est the hypothesis that synergy may occur between cotinine and bacterial pr oducts isolated from 3 putative periodontopathogens. Methods: A chick embryo toxin assay was used to investigate bacterial toxin s (cell-free extracellular toxins and cell-free cell lysates) from 5 specie s with and without cotinine. A total of 9 putative periodontopathogens (3 s pecies) and 2 non-oral controls (2 species) were studied. The periodontal s pecies were: Prevotella intermedia (n = 4), Prevotella nigrescens (n = 4), and Porphyromonas gingivalis (n = 1). The control species tested were: Stap hylococcus aureus (n = 1) and Escherichia coli (n = 1). Results: The toxicity kill was significantly greater than expected by simpl e addition alone (P <0.05, Fisher's exact test) between cotinine (800 ng/ml ) and 1) the cell-free extracellular toxins of P. nigrescens MH1 and 2) the cell-free cell lysates of P. intermedia MH2. Synergy occurred with cotinin e plus the cell-free extracellular toxins in all but 3 periodontal isolates , and the cell-free cell lysates in all but 2 periodontal isolates. Cotinin e significantly (P <0.05, Fisher's exact test) enhanced the effects off cel l-free extracellular toxins and cell lysates from one central species (E. c oli), but not the other (S. aureus). Conclusions: These findings indicate that synergy in an in vitro assay can occur between cotinine and toxins from putative periodontopathogens. This m ay be one important mechanism by which smoking increases the severity of pe riodontitis.