Characteristics of Porphyromonas gingivalis lipopolysaccharide in co-culture with Fusobacterium nucleatum.

Porphyromonas gingivalis is associated with chronic periodontitis and forms multi-species biofilms. They can communicate within species as well as with other species found in the subgingiva, which may induce changes in the growth ratio and virulence of periodontopathogens. The lipopolysaccharide (LPS) of P. gingivalis shows different virulence by growth condition. The purpose of this study was to investigate the characteristics of P. gingivalis LPS when co-cultured with Fusobacterium nucleatum. After culture of P. gingivalis in the presence or absence of F. nucleatum, P. gingivalis LPS was extracted. THP-1 cells were treated with the LPS and induction of cytokine expression was investigated using real-time reverse transcription polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). For the analysis of P. gingivalis LPS, LPS biosynthesis-related genes such as lpxA and lpxD were evaluated with real-time RT-PCR. Finally, molecular mass of lipid A was measured by mass spectrometry after hydrolysis of the LPS. Co-cultured P. gingivalis LPS exhibited higher induction of expression of interleukin 1β, 6, and 8 than single-cultured P. gingivalis LPS. These symptoms may be caused by an increase in m/z 1689 lipid A through the upregulation of lpxA and lpxD expression by communication between P. gingivalis and F. nucleatum.