Abstract
Porphyromonas gingivalis is a keystone pathogen of periodontitis. Outer membrane vesicles (OMVs) have been considered as both offense and defense components of this bacterium. Previous studies indicated that like their originating cells, P. gingivalis vesicles, are able to invade oral epithelial cells and gingival fibroblasts, in order to promote aggregation of some specific oral bacteria and to induce host immune responses. In the present study, we investigated the invasive efficiency of P. gingivalis OMVs and compared results with that of the originating cells. Results revealed that 70–90% of human primary oral epithelial cells, gingival fibroblasts, and human umbilical vein endothelial cells carried vesicles from P. gingivalis 33277 after being exposed to the vesicles for 1 h, while 20–50% of the host cells had internalized P. gingivalis cells. We also detected vesicle-associated DNA and RNA and a vesicle-mediated horizontal gene transfer in P. gingivalis strains, which represents a novel mechanism for gene transfer between P. gingivalis strains. Moreover, purified vesicles of P. gingivalis appear to have a negative impact on biofilm formation and the maintenance of Streptococcus gordonii. Our results suggest that vesicles are likely the best offence weapon of P. gingivalis for bacterial survival in the oral cavity and for induction of periodontitis.
Highlights
Bacterial vesicles are produced generally by Gram-negative bacteria through the blebbing and pinching-off of the bacterial outer membrane [1]
To expose human oral keratinocytes (HOK), Human gingival fibroblasts (HGF), and human umbilical vein endothelial cells (HUVEC) to P. gingivalis 33277 cells or their vesicles, host cells (2 × 104) were cultured with P. gingivalis cells (2 × 106) or vesicles (100 ng, equivalent to vesicles released by 2 × 104 of P. gingivalis in late log-phase) [18] for 1 h
By counting 10 random areas (1.34 × 1.34 mm), we found that 82 ± 5.4, 69 ± 6.5, and 80 ± 13.4% of the HOKs, HGFs, and HUVECs engulfed vesicles 3 h post exposure, respectively, and up to 85 ± 7.1, 93 ± 2.9, and 87 ± 6.9% of the HOKs, HGFs, and HUVECs contained the vesicles after a 24 h exposure (Fig 1B, 1C, and 1D)
Summary
Bacterial vesicles are produced generally by Gram-negative bacteria through the blebbing and pinching-off of the bacterial outer membrane [1]. Biller et al recently demonstrated that vesicles in the culture medium of Porchlorococcus were as abundant as the number of cells in early growth phase, while they were 10 times as numerous as the number of cells found in the exponential and stationary phases [2]. As they carry many of the virulence factors found in bacterial outer membranes and the periplasm, vesicles are known to be an efficient vehicle involved in the pathogenicity of Gram-negative bacteria. Studies have shown that vesicles are involved in adherence, biofilm formation, invasion, host
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