Effects of Porphyromonas gingivalis and Streptococcus gordonii on Cell Cycle

Microarray analysis has shown that distinct pathways of gingival cells are modulated upon infection with oral species; cell cycle control being one of the most differentially impacted pathways by these interactions.  Objective:  This study  examined the cell cycle kinetic progression of oral epithelial cells challenged with single and mixed cultures of commensal and pathogenic species.  Methods:  Human immortalized gingival keratinocytes (HIGK) were co-cultured with  P. gingivalis and S. gordonii for 4 hours in mono- and mixed-cultures,  washed, treated with gentamicin (300 ug/ml) and metronidazole (200 ug/ml) and allowed to grow for an additional 20 hours.  Cell cycle kinetics were measured using immunofluorescent staining and analyzed using fluorescence-activated cell sorting (FACS Calibur, Becton Dickerson).  Results:  The proportion of HIGK in different cell cycles varied whether HIGK cells were infected with mono- and mixed cultures of P. gingivalis and/or S. gordonii.  At 24 hours, 53.4% of uninfected HIGK cells were in S-phase as compared to mono-infected with P. gingivalis (44.9%), mono-infected with S. gordonii (73.2%), and mixed-infected (62.7%).  Otherwise, uninfected  cells were in the G₀/G₁ phases (10.56%) and G2 + M phases (11.8%), while P. gingivalis-infected were in G₀/G₁ phases (12.3%) and in G2 + M phases (15.5%). A lower (p<0.05) numbers of cells were found in these phases when HIGK were mono- or co-infected with S. gordonii. Conclusion: Infection with S. gordonii resulted in the majority of HIGK remaining in S phase while infection with P. gingivalis resulted in a wider distribution of HIGK in each of the various stages of cell cycling. Introducing commensal S. gordonii to P. gingivalis-infected HIGK cells promoted progression of HIGK into S-phase of the cell-cycle, shifting the trend towards the commensal species.  Acknowledgements:  This study was supported by NIH/NIDCR DE16715 (MH), a UFCD Student Summer Research Fellowship, and NIH/NIDCR T32 Grant DE007200.