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Infection and Immunity, January 2006, p. 703-710, Vol. 74, No. 1
0019-9567/06/$08.00+0     doi:10.1128/IAI.74.1.703-710.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Intercellular Spreading of Porphyromonas gingivalis Infection in Primary Gingival Epithelial Cells

Department of Pathobiology, University of Washington, Seattle, Washington 98195,¹ Institut Jacques Monod, Université Paris 7, 75251 Paris Cedex 5, France,² Department of Oral Biology, College of Dentistry, University of Florida, Gainesville, Florida 32610,³ School of Natural Sciences, University of California, Merced, California 95344⁴

Received 21 July 2005/ Returned for modification 24 August 2005/ Accepted 7 September 2005

Porphyromonas gingivalis, an important periodontal pathogen, is an effective colonizer of oral tissues. The organism successfully invades, multiplies in, and survives for extended periods in primary gingival epithelial cells (GECs). It is unknown whether P. gingivalis resides in the cytoplasm of infected cells throughout the infection or can spread to adjacent cells over time. We developed a technique based on flow cytofluorometry and fluorescence microscopy to study propagation of the organism at different stages of infection of GECs. Results showed that P. gingivalis spreads cell to cell and that the amount of spreading increases gradually over time. There was a very low level of propagation of bacteria to uninfected cells early in the infection (3 h postinfection), but there were 20-fold and 45-fold increases in the propagation rate after 24 h and 48 h, respectively, of infection. Immunofluorescence microscopy of infected cells suggested that intercellular translocation of P. gingivalis may be mediated through actin-based membrane protrusions, bypassing the need for release of bacteria into extracellular medium. Consistent with these observations, cytochalasin D treatment of infected cells resulted in significant inhibition of bacterial spreading. This study shows for the first time that P. gingivalis disseminates from cell to cell without passing through the extracellular space. This mechanism of spreading may allow P. gingivalis to colonize oral tissues without exposure to the humoral immune response.

Editor: D. L. Burns

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