P. gingivalis transmission into new host cells does not require cell-to-cell contact. This is demonstrated using the Transwell inserts to separate initially infected from subsequently added host cells. The initial infected cells were spin inoculated at M.O.I. of 100. Twenty-four hours later, 2 × 104 invaded cells were harvested and seeded into a Transwell insert. The insert was placed on top of 8 × 104 uninfected cells. Following combinations were tested. 1) Transmission from the insert with infected EC (iEC) to SMC at the bottom compartment; 2) Transmission from iEC to KB cells; 3) Transmission from iSMC to SMC; and 4) Transmission from iSMC to KB. After 24 hour incubation with the Transwell insert, the cells at the bottom were fixed. For P. gingivalis, anti-P. gingivalis antibody, 61BG1.3 was used, followed by Cy3-labeled secondary antibody. For SMC, anti-smooth muscle actin antibody was used followed by FITC-labeled secondary antibody. Blue, DAPI staining. Red, Pg; Blue, DAPI; Green, SMA. Scale bar is 50 μm.