Tobacco Smoke Augments Porphyromonas gingivalis - Streptococcus gordonii Biofilm Formation

Juhi Bagaitkar,Carol K Patel,Donald R Demuth,David A Scott,Diane E Renaud,Carlo A Daep,Roy Martin Roop Ii

doi:10.1371/journal.pone.0027386

Abstract

Smoking is responsible for the majority of periodontitis cases in the US and smokers are more susceptible than non-smokers to infection by the periodontal pathogen Porphyromonas gingivalis. P. gingivalis colonization of the oral cavity is dependent upon its interaction with other plaque bacteria, including Streptococcus gordonii. Microarray analysis suggested that exposure of P. gingivalis to cigarette smoke extract (CSE) increased the expression of the major fimbrial antigen (FimA), but not the minor fimbrial antigen (Mfa1). Therefore, we hypothesized that CSE promotes P. gingivalis-S. gordonii biofilm formation in a FimA-dependent manner. FimA total protein and cell surface expression were increased upon exposure to CSE whereas Mfa1 was unaffected. CSE exposure did not induce P. gingivalis auto-aggregation but did promote dual species biofilm formation, monitored by microcolony numbers and depth (both, p<0.05). Interestingly, P. gingivalis biofilms grown in the presence of CSE exhibited a lower pro-inflammatory capacity (TNF-α, IL-6) than control biofilms (both, p<0.01). CSE-exposed P. gingivalis bound more strongly to immobilized rGAPDH, the cognate FimA ligand on S. gordonii, than control biofilms (p<0.001) and did so in a dose-dependent manner. Nevertheless, a peptide representing the Mfa1 binding site on S. gordonii, SspB, completely inhibited dual species biofilm formation. Thus, CSE likely augments P. gingivalis biofilm formation by increasing FimA avidity which, in turn, supports initial interspecies interactions and promotes subsequent high affinity Mfa1-SspB interactions driving biofilm growth. CSE induction of P. gingivalis biofilms of limited pro-inflammatory potential may explain the increased persistence of this pathogen in smokers. These findings may also be relevant to other biofilm-induced infectious diseases and conditions.

Highlights

Periodontitis is an infectious, chronic inflammatory disease of the supportive structures of the teeth
Our previous studies suggested that exposure to cigarette smoke extract (CSE) augments the expression of the major fimbrial antigen of P. gingivalis (FimA) at the transcriptional and protein levels, while simultaneously down-regulating capsular polysaccharides [15,28]
CSE exposure has no effect on the absolute protein level of the minor fimbrial antigen of P. gingivalis (Mfa1; Figure 1A and B) or on Mfa1 surface presentation, as assessed by availability to anti-Mfa1 antibodies (Figure 1C)

Summary

Introduction

Periodontitis is an infectious, chronic inflammatory disease of the supportive structures of the teeth. Smokers often exhibit periodontal disease that is more severe than in non-smokers, with increased alveolar bone loss [1], attachment loss [2], tooth mobility, and tooth loss [3] all apparent and odds ratios of 3 to 7 commonly reported [4]. In periodontitis there is a bacterial succession to a microflora rich in Gram negative, obligate anaerobes that is responsible for the onset and progression of disease [8,9]. Multiple studies have shown that smokers are more likely to be infected with the key etiological agent of periodontitis, P. gingivalis, to harbor higher numbers of P. gingivalis, and to exhibit more persistent infection by this pathogen [11,12,13,14], relative to non-smokers

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Results

Conclusion