MIXED INFECTION WITH PORPHYROMONAS-GINGIVALIS AND FUSOBACTERIUM-NUCLEATUM IN A MURINE LESION MODEL - POTENTIAL SYNERGISTIC EFFECTS ON VIRULENCE

These studies determined the characteristics of tissue destruction in a murine abscess model elicited by mixed infection with the periodonto pathogens Fusobacterium nucleatum and Porphyromonas gingivalis. The in terbacterial effects of this synergism, the kinetics of the relationsh ip of the bacterial interaction, and the characteristics of the bacter ia required for the tissue destruction were studied. Infection of mice with P. gingivalis and F. nucleatum strains elicited lesions of vario us sizes as a function of infective dose. Primary infection with F. nu cleatum plus P. gingivalis at various ratios (i.e., <1:1) resulted in a significantly greater lesion size (P < 0.001) compared with that res ulting from primary infection with P. gingivalis alone. At F. nucleatu m/P. gingivalis ratios of greater than or equal to 1:1, spreading lesi on formation and progression were significantly (P < 0.001) decreased, suggesting that bacterial interaction (i.e., coaggregation) may have inhibited the spread of the P. gingivalis infection to a site distant from the initial injection. Infection with F. nucleatum and P. gingiva lis simultaneously (at different sites) or F. nucleatum administered w ithin 4 h prior to or 1 h following P. gingivalis infection significan tly enhanced the ability of P. gingivalis to form large phlegmonous le sions. Chemical inhibition of the P. gingivalis trypsin-like protease activity or the use of a trypsin-negative P. gingivalis strain abrogat ed tissue destruction either alone or in combination with F. nucleatum . Therefore, it was possible to examine aspects of virulence of these pathogens in a murine lesion model by either altering bacterial ratios , manipulating the time of infection, or targeting vital bacterial vir ulence factors.