Int. J. Mol. Sci. 2013, 14(8), 17221-17237; doi:10.3390/ijms140817221

Review
Environmental Stimuli Shape Biofilm Formation and the Virulence of Periodontal Pathogens
Marja T. Pöllänen 1,,*, Annamari Paino 2 and Riikka Ihalin 2,
1
Institute of Dentistry, University of Turku, FI-20014 Turku, Finland
2
Department of Biochemistry and Food Chemistry, University of Turku, FI-20014 Turku, Finland; E-Mails: aepain@utu.fi (A.P.); riikka.ihalin@utu.fi (R.I.)
These authors contributed equally to this work.
*
Author to whom correspondence should be addressed; E-Mail: marpol@utu.fi; Tel.: +358-40-723-58-18.
Received: 1 July 2013; in revised form: 2 August 2013 / Accepted: 7 August 2013 /
Published: 20 August 2013

Abstract

: Periodontitis is a common inflammatory disease affecting the tooth-supporting structures. It is initiated by bacteria growing as a biofilm at the gingival margin, and communication of the biofilms differs in health and disease. The bacterial composition of periodontitis-associated biofilms has been well documented and is under continual investigation. However, the roles of several host response and inflammation driven environmental stimuli on biofilm formation is not well understood. This review article addresses the effects of environmental factors such as pH, temperature, cytokines, hormones, and oxidative stress on periodontal biofilm formation and bacterial virulence.
Keywords:
periodontal pathogens; environmental stimuli; biofilm EPS; virulence factors

1. Introduction

Periodontitis is a common disease affecting the tooth-supporting structures of millions of people worldwide, and it is a multifactorial disease initiated by bacteria growing as a biofilm at the gingival margin. Periodontal biofilms are diverse, and the nature and communication of these biofilms differs in health and disease. The bacterial composition of periodontitis-associated biofilms has been well documented and is under constant analysis. Several key pathogens have been identified: Porphyromonas gingivalis, Treponema denticola, Tannerella forsythia, Aggregatibacter actinomycetemcomitans and more recently also Filifactor alocis, Staphylococcus aureus and the genus Desulfobulbus [14]. In addition to bacteria, viruses are commonly detected from periodontal lesions and subgingival plaque samples of patients with aggressive periodontitis [5,6]. Furthermore, the association of the biofilm-forming yeast Candida albicans has been detected in approximately 50% of severe chronic periodontitis patients and in only 15% of subgingival samples isolated from healthy patients [7]. Periodontal biofilm formation is a stepwise and continuous process. In the initial phase, the gram-positive and aerobic bacteria dominate. Later, the gram-negative anaerobic periodontopathogens increase in the biofilm. Clinically, the course of periodontitis leads to increased subgingival inflammation and formation of periodontal pockets. The subgingival environment is ideal for the periodontopathogens, being alkaline, hemin and protein rich with various cytokines and hormones. The bacterial cells in biofilm are surrounded by extracellular polymeric substance (EPS), which is composed of polysaccharides, proteins and extracellular DNA, and may account for as much as 90% of the total mass of the biofilm [810]. The EPS protects pathogens from host defence cells, such as macrophages, and humoural immune defence factors, such as antibodies and complement, as well as antibiotics. In addition, the high bacterial cell densities in biofilm enable small molecule mediated inter- and intra-species crosstalk, i.e., quorum sensing, which itself may regulate virulence gene expression via pathogens. Moreover, both the host response and the environmental factors in periodontitis can affect the biofilm formation and virulence gene expression of periodontal pathogens (Figure 1). We discuss this crosstalk network of molecular interactions in this review article.

2. Host Inflammatory Reaction-Related Stimuli

The oral environment is an ideal, nutrient-rich, warm and growth-promoting place for bacteria to form communities. This first part of the digestive tract offers the bacteria perfect non-shedding surfaces of the teeth to attach and multiply. The bacterial biofilm on the tooth surface activates both the innate and adaptive host responses, which, in turn, have an effect on the biofilm. The first-line host defence is initiated by the polymorphonuclear (PMN) leukocytes that are recruited to the site by chemotactic factors, e.g., the gradient of IL-8 and ICAM-1 in the junctional epithelium [11]. In the subgingival area, the temperature increases, and the inflammatory reaction causes the release of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) and superoxide (O2•−), and cytokines from the host cells to destroy the bacteria. However, the bacterial biofilm is a community, and not only the bacteria but also their virulence and the EPS surrounding them may be affected and changed by the changes produced during the inflammation process.

2.1. Temperature

Changes in the environmental temperature have an effect on various functions and virulence of diverse microbial species. Bacteria can sense changes in temperature by proteins, e.g., transcriptional regulators, kinases (e.g., histidine kinase in association with a cytoplasmic response regulator) and chaperones, and via their membrane lipids (for a review see [12]). In the periodontal pocket, an approximately 2 °C increase in the local subgingival temperature has been reported in diseased sites compared with healthy sites [13]. The temperature increase is a host defence mechanism that triggers virulence and heat shock gene expression in bacteria in response [12]. However, the temperature increase also affects the attachment of bacteria, coaggregation of bacteria, and protease production [1417]. P. gingivalis has displayed decreased expression of proteases and down-regulation of the genes coding fimbrial proteins in response to temperature elevation [15,16]. Furthermore, the structure of lipid-A in P. gingivalis also appears to be affected by temperature. In elevated temperature environments, increasing amounts of monophosphorylated penta-acylated lipid A are expressed [18]. This lipid A form in turn appears to be a more potent activator of the host Toll-like receptor 4 (TLR4) and further renders the bacteria more susceptible to host defensins [18]. However, the net effect of the temperature increase seems to favour the periodontal pathogens in subgingival biofilms because increased proportions of Prevotella intermedia, P. gingivalis and A. actinomycetemcomitans have been reported in sites with elevated temperatures [19].

2.2. Oxidative Stress

ROS generation, as a part of the host defence mechanism or from the initial Streptococcal colonisers in the biofilm, induces oxidative stress in other biofilm bacteria and especially in the anaerobic species of the community. The anaerobic bacteria sense the levels of ROS by transcriptional regulators such as OxyR, PerR and OhrR. Superoxide dismutases, alkyl hydroperoxide reductase (AhpC) and catalases are produced by the bacteria for the detoxification of the ROS [20,21]. In the periodontal biofilm community, F. nucleatum is important as an intermediate coloniser between the early Streptococcal and late anaerobic periodontopathogenic colonisers. F. nucleatum appears to facilitate the survival of other anaerobic bacteria in the biofilm [22]. Although an obligate anaerobe, F. nucleatum can adapt to oxidative stress in the biofilm and even increase in number in aerobic conditions for up to 2 days [23,24]. The response of F. nucleatum to oxidative stress appears to be mediated by the AhpC redox system [25]. Furthermore, the oxidative stress appears to also alter the carbohydrate metabolism of F. nucleatum by modifying or increasing the intracellular concentrations of glycolytic enzymes, thereby decreasing ATP production. Increases in the chaperone proteins ClpB and DnaK, the heat shock protein HtpG and the transcription repressor HrcA in F. nucleatum in oxidative stress conditions appear to be aimed at diminishing the harmful effects of ROS [25]. In addition, the periodontopathogens have developed strategies to adapt to oxidative stress. For example, P. gingivalis produces superoxide dismutase, AhpC, rubrerythrin (rbr), heat shock proteins (HtpG) and chaperons GroEL and DnaK when challenged with oxidative stress [26]. Similarly, elevated inflammatory temperatures upregulate the expression of superoxide dismutase in P. gingivalis [27]. Furthermore, the expression of several genes with unknown functions has been observed to be altered in P. gingivalis under oxidative stress [28].

2.3. Inflammatory Cytokines

In periodontitis, during the active phases of the tissue destruction, the periodontal tissue and gingival fluid typically contain high levels of proinflammatory mediators such as interleukin (IL)-1β [3,29,30]. This overexpression of IL-1β results in host tissue damage, which is characteristic for periodontal disease and aimed at eliminating pathogens together with the regulation of the immune response [3133]. In periodontium, cytokines are released by first-line human defence cells after identification of periodontopathogens and bacterial products. For instance, gingival epithelial cells and fibroblasts can secrete IL-1β after P. gingivalis and A. actinomycetemcomitans infection or after being cultured in the presence of Treponema denticola lipooligosaccharides [34,35]. Oral bacteria-derived compounds, such as leucotoxins and lipopolysaccharides of A. actinomycetemcomitans, induce IL-1β secretion in macrophages [36,37]. Macrophages and monocytes are considered the main producers of IL-1β during inflammation [3840]. As a key conductor of the inflammatory response, IL-1β induces the release of other proinflammatory mediators [34,41]. Thus, the release of IL-6 and IL-8 from gingival epithelial cells during periodontal infection can be hindered by blocking induction of IL-1β induction [34]. Tumour necrosis factor-alpha (TNF-α), IL-6 and IL-8 are cytokines commonly released by epithelial cells after bacterial infection [4245]. Recent studies suggest that the gingival cell response differs when infected with oral biofilm [46] or with multispecies biofilms ([47]; reviewed in [48]) as compared with planktonic bacterial infection.

Human IL-1β, crucial for the host battle against pathogens, might also be sensed by host-colonising microbes. The first evidence of bacterial response against cytokines was observed in studies with virulent Escherichia coli strains over 20 years ago. It was shown that E. coli cells can bind IL-1β and that the growth of these strains increased after IL-1β exposure, whereas treatment with IL-4 or TNF-α was ineffective. Moreover, the use of decoy receptor IL-Ra for IL-1β reversed the growth-promoting effect in E. coli. [49] Later, it was demonstrated that other bacterial species such as Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter spp. can alter their growth properties as a consequence of exposure to IL-1β, IL-6 or TNF-α [50].

Gram-positive S. aureus has been a central model species for studies of the role of IL-1β in pathogen-cytokine crosstalk. Surprisingly, S. aureus, which is most often associated with nasal passages and skin, was also identified from subgingival plaques in 60% of aggressive periodontitis patients belonging to a group of non-smokers [4]. According to an in vitro experiment, the growth of S. aureus biofilms increases when cultured in the presence of IL-1β [51,52]. The growth enhancement was also observed with two linear peptide fragments (<5 kDa) of human IL-1β [53]. In addition to growth enhancement, the cytokine modulated the gene expression of S. aureus biofilms. The cytokine decreased the gene expression of some toxin-encoding genes and increased the expression of host tissue-attachment responsible genes [54].

The hypothesis concerning the capability of the bacteria to specifically bind IL-1β was strengthened by the characterisation of a specific bacterial outer membrane receptor for IL-1β in gram-negative Yersinia pestis. The IL-1β-interacting protein is known as a capsule antigen F1 assembly protein (Caf1A), which contributes to capsule antigen (Caf1) transportation across the outer membrane [55]. Interestingly, Caf1 displays 28% sequence homology with human IL-Ra [56]. The second bacterial cytokine receptor, the outer membrane protein OprF, which binds only human interferon-γ, was initially observed in gram-negative P. aeruginosa. As a response to cytokine binding, P. aeruginosa increased lectin-encoding gene (lecA) expression in a quorum sensing dependent manner [57]. The hydrophobic galactose-binding lectin localised in the EPS of P. aeruginosa biofilms contributes to species biofilm formation and endothelial cell adherence [58].

Cytokines, such as IL-1α, IL-1β, IL-2, IL-3, IL-4, IL6, IL-7 [59] and TNF [60], use their carbohydrate-binding domains to recognise specific oligosaccharide ligands (reviewed in [61]). The receptor-binding site of IL-1 associates with its cognate receptor, and the second domain, localised opposite to the receptor binding sites, interacts with carbohydrate. For instance, IL-1α and IL-β have different carbohydrate binding activities. Whereas IL-1α binds N-glycan with two α-2–3-linked sialic acid residues, IL-1β recognises the α2–3-sialylated β-galactosyl-ceramides, which have very long and unusual long-chain bases [62]. Moreover, some lipooligosaccharides of Haemophilus species are sialylated, and they encode sialyltransferases [63,64].

A. actinomycetemcomitans is the only major periodontopathogen to our knowledge that has been shown to both sense and bind IL-1β. The clinical strains of the species display a physiological response to cytokines by decreasing their metabolism and by increasing their biofilm mass [65]. A. actinomycetemcomitans biofilms co-cultured with an organotypic gingival mucosa model bind IL-1β, but the use of antibiotics during co-culturing inhibits IL-1β binding [66]. Moreover, the species appears to uptake IL-1β as the cytokine has been detected in the intracellular space of the bacterium [66]. Two intracellular proteins, the trimeric form of ATP synthase subunit β and bacterial histone-like protein HU, have displayed interaction with human IL-β [65,66]. The interaction of internalised IL-1β with a key protein in cellular energy production and genomic DNA condensing HU protein might explain the above-described physiological responses of A. actinomycetemcomitans. These results suggest that viable A. actinomycetemcomitans cells possess a specific uptake mechanism for IL-1β. According to our recent results, A. actinomycetemcomitans encodes a Pasteurellaceae-specific outer membrane lipoprotein responsible for IL-1β interaction [67]. In addition to bacterial species, herpesviruses and yeasts found in subgingival biofilms can sense and bind the cytokines produced by the host [68,69].

3. Periodontitis-Associated Environmental Factors

Various environmental factors, other than those strictly related to the inflammatory response of the host, may change during the progression of periodontitis. Such factors include, for example, pH, the concentration of iron and hemin, and the presence of various host hormones. All these factors can be sensed by at least some of the periodontal pathogens, although studies at the molecular level are scarce. However, the results obtained thus far suggest that elevated pH and iron limitation may enhance the biofilm formation of some species and influence virulence gene expression, which, in turn, might alter the host inflammatory response.

3.1. Alkaline pH

The environment of the periodontitis-associated gingival pocket, and especially the gingival crevicular fluid, is characterised by alkaline pH, which may rise above 8.5 [7072]. Some periodontal pathogens, such as P. gingivalis, P. intermedia and F. nucleatum, are able to elevate the ambient pH by fermenting amino acids in vitro [73], a feature which may also alkalify the microenvironment in subgingival biofilm locally.

An alkaline pH of 8.2 has been shown to increase cell surface hydrophobicity as well as induce the co-adhesion and biofilm formation of F. nucleatum, which is accompanied by decreased intracellular polyglucose content and elongation of individual cells [74]. When grown at a slightly lower pH than 8.2, i.e., at pH 7.8, F. nucleatum cells display upregulated expression of the enzyme formiminotetrahydrofolate cyclodeaminase, which could be involved in raising the surrounding pH value [75]. In addition, the production of a non-iron redox acceptor flavodoxin, the expression of which is typically upregulated in iron-limited growth conditions [76], was also observed to be upregulated in alkaline pH conditions [75]. F. nucleatum cells appear to change their metabolism in response to high pH, because some enzymes of the glycolytic pathway, as well as glutamic acid and histidine catabolism, are downregulated in planktonic cells grown at an alkaline pH of 7.8 [75]. However, when the pH is further raised to 8.2, which induces biofilm formation, the amounts of glycolytic enzymes do not increase, whereas glucose storage and lactate production increases [77]. In contrast to increased glucose storage, the production of various proteins involved in protein synthesis decrease at high pH values in F. nucleatum biofilm [77]. At pH 8.2, another change in the expression of metabolic enzymes is the increased production of glutamate dehydrogenase, which might indicate that the bacterium adjusts its metabolism to the increased concentration of glutamate in the gingival crevicular fluid associated with inflamed periodontal tissue [77]. The cellular stress response in bacteria might also be activated at an alkaline pH because F. nucleatum cells upregulate the expression of peptidyl-prolyl cis-trans isomerase (PPI) and the heat-shock protein GroEL [75,77]. Of these proteins, GroEL might have a role in the host-bacterium crosstalk because GroEL-like proteins may modulate the host immune response, as shown with F. nucleatum [78] and A. actinomycetemcomitans [79]. Moreover, GroEL might be a link between periodontitis and systemic diseases, such as atherosclerosis, as F. nucleatum GroEL induces various risk factors of atherosclerosis in mice [80].

Whereas some of the pH-regulated intracellular proteins may alter the virulence of the bacterium, one interesting group of pH-regulated proteins are expressed in the cellular envelope of the bacterial cell. In particular, the proteins that are involved in adhesion to other periodontal pathogens as well as to host cells may play important roles in virulence. When F. nucleatum was grown at an alkaline pH of 8.2, elevated levels of FomA adhesion isoforms were detected [77]. FomA may function as recruiter of other periodontal pathogens, such as P. gingivalis, [81], and has been proven to be a possible vaccine target in a mouse study [82]. Some of the downregulated cellular envelope proteins of F. nucleatum are involved in ATP synthesis and maintenance of a neutral cyto- or periplasmic pH, indicating decreased metabolic activity and adjustment to alkaline conditions, respectively [83]. Some of the downregulated proteins likely have dual roles, as in the case of butyrate-acetoacetate CoA transferase, which is involved both in energy metabolism and, as a virulence factor, butyric acid production [83]. The group of cellular envelope proteins that were upregulated at an alkaline pH contained at least two putative surface antigens: outer membrane protein (OMP), belonging to the Omp IP family of porins, and a pathogen-specific membrane antigen that was predicted to have high affinity to Fe2+[83]. In addition to the Omp IP family porins, the expression levels of various transporter proteins was altered when F. nucleatum cells were grown in biofilm at a pH of 8.2, which could be an indication of a changed need to uptake various solutes from the microenvironment in the biofilm [77]. Most of the studies that have investigated the effects of alkaline environment on periodontal pathogens have been performed in F. nucleatum. However, up to 50% of the alkaline pH-regulated genes coding F. nucleatum cell envelope proteins could have been acquired through horizontal gene transfer, and similar proteins are also found in other periodontal pathogens, such as P. gingivalis and Treponema denticola [83].

3.2. Iron and Hemin

Because free iron catalyses the formation of toxic free radicals from H2O2 and is essential for the function of both the host and the pathogenic bacteria, human organs have developed complex ways to limit the availability of free iron in the environment [84]. Thus, the environment that surrounds potential colonisers when they enter a human host is suboptimal in terms of free iron concentration. Most of the host iron is bound to iron-binding proteins such as transferrin, ferritin, lactoferrin and haemoglobin that contain hemin or haem. However, the situation may change during the progression of periodontitis. It has been hypothesised that the concentration of hemin may increase due to the increasing concentration of haemoglobin leaking from vascular ulcers of the gingival pocket. Some periodontal pathogens, such as P. gingivalis, T. denticola and A. actinomycetemcomitans, have been demonstrated to express hemin-binding proteins on their surfaces [8587] that may facilitate iron acquisition in free iron-limited conditions. Moreover, hemin may also directly regulate the virulence characteristics of P. gingivalis [88].

Iron chelation has been shown to increase the expression of the EPS-, fimbrial-, and LPS-related genes, pgaC, tadV, and rmlB, respectively, in A. actinomycetemcomitans, which also leads to increased biofilm formation [89]. The effect of limited concentrations of iron most likely is mediated by small regulatory RNAs (sRNA) in A. actinomycetemcomitans, though the target genes for these sRNAs, have not been yet identified [90]. The most studied periodontal pathogen, regarding the need and effects of iron on the bacterium, is likely P. gingivalis. In agreement with being an essential growth factor and important cause of oxidative stress (for review see [9]), iron limitation upregulates the genes involved in iron uptake and downregulates the genes associated with the storage of iron as well as the oxidative stress response of P. gingivalis [9]. Moreover, by limiting iron and hemin availability, the host can also increase biofilm formation, the invasion of single bacterial cells to the host cells [9], and increase vesicle secretion and protease production of P. gingivalis [91]. Another potential virulence factor of P. gingivalis that is regulated by hemin is LPS, and more specifically, the lipid A form of it [88]. A form of lipid A, which is a Toll-like receptor (TLR) 4 antagonist, is produced at high hemin concentrations, whereas at low hemin concentrations TLR4-agonist lipid A is the major form, suggesting that P. gingivalis can alter the host response with the changing hemin microenvironment [88].

3.3. Hormones

Although various bacterial species are known to respond to the stress-related hormones adrenaline and noradrenaline, and the molecular players of their sensory machinery have been clarified in detailed (reviewed in [92]), the periodontal pathogens have been little studied. In the first study that investigated the effects of catecholamines, noradrenaline and adrenaline, on periodontal bacteria, both negative and positive growth effects on planktonic species were reported [93]. However, both catecholamines inhibited the growth of “red complex” [94] periodontal pathogens P. gingivalis and T. forsythia (formerly Bacteroides forsythus) as well as A. actinomycetemcomitans serotypes a and b and F. nucleatum [93]. Thus, the authors stressed the importance of negative growth effects and hypothesised that these species might also use catecholamines to enhance virulence gene expression [93]. A recent study by Saito et al. [95] demonstrated that growth inhibition of P. gingivalis by noradrenaline is accompanied with enhanced production of the virulence-associated protease arg-gingipain B and downregulation of the genes coding polysaccharide biosynthesis-related proteins.

The most significant rise in the levels of the female sex hormones, oestrogen and progesterone, occurs during pregnancy [96]. Although pregnancy gingivitis is currently categorised under the class of “dental plaque-induced gingival diseases modified by the endocrine system” [97], the effects of hormone levels on the progression of gingivitis during pregnancy is still under debate [98100]. It appears that even though gingival inflammation may intensify during pregnancy, the hormones themselves may cause controversial changes in the periodontium, including decreased inflammatory reactions [101104] and changes in the composition of subgingival biofilm [105107]. Moreover, some gram-negative periodontal pathogens, such as Prevotella melaninogenica, P. intermedia and P. gingivalis are able to take up estradiol and progesterone, which the Prevotella species may use as a growth factor instead of vitamin K [108]. However, whether these hormones affect the biofilm formation and the virulence of periodontal pathogens is not known.

4. Conclusions

In periodontitis, the crosstalk between the host and the bacterial biofilm is diverse and bidirectional. The host response and environmental changes induce stress in the biofilm bacteria (Table 1). Elevated temperature of the subgingival environment, though aimed to eliminate the pathogens appears to only decrease virulence factors in pathogens (e.g., proteases in P. gingivalis) and does not sufficiently eliminate the pathogens [19]. The change in the local pH towards an alkaline environment appears to play an important role in the shift towards periodontopathogenic biofilm composition. The biofilm mass is increased in alkaline conditions and, in particular, the intermediate coloniser F. nucleatum displays increased adhesion and coaggregation with other bacteria. Oxidative stress and the inflammatory cytokine IL-1β result in decreased metabolism in periodontal biofilm but still increase various virulence factors as well as biofilm formation. The limited amount of free iron appears to enhance biofilm EPS formation [89]. During periodontal inflammation, the increased amount of hemin might downregulate the expression of bacterial virulence factors and upregulate the expression of immune-suppressing molecules. In summary, the environmental changes generated in inflammation favour biofilm formation and appear to drive the bacteria into the shelter provided by the EPS and the lower metabolic activity. The inflammatory environment with active immune cells and a hostile humoural response is not ideal for planktonic bacteria, which are released by mature biofilm when expanding to new habitats. Biofilm formation might explain the onset of less progressive phases in periodontal inflammation and tissue destruction and allow the periodontal pathogens to persist in subgingival spaces.

Acknowledgments

Biofilm research in the Ihalin laboratory has been funded by the Academy of Finland, the Paulo Foundation, the Ella and Georg Ehrnrooth Foundation, the Turku University Foundation and the Finnish Dental Society Apollonia.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Bartold, P.M.; van Dyke, T.E. Periodontitis: A host-mediated disruption of microbial homeostasis. Unlearning learned concepts. Periodontol 2000 2013, 62, 203–217.
  2. Griffen, A.L.; Beall, C.J.; Campbell, J.H.; Firestone, N.D.; Kumar, P.S.; Yang, Z.K.; Podar, M.; Leys, E.J. Distinct and complex bacterial profiles in human periodontitis and health revealed by 16S pyrosequencing. ISME J 2012, 6, 1176–1185.
  3. Rescala, B.; Rosalem, W., Jr; Teles, R.P.; Fischer, R.G.; Haffajee, A.D.; Socransky, S.S.; Gustafsson, A.; Figueredo, C.M. Immunologic and microbiologic profiles of chronic and aggressive periodontitis subjects. J. Periodontol. 2010, 81, 1308–1316.
  4. Fritschi, B.Z.; Albert-Kiszely, A.; Persson, G.R. Staphylococcus aureus and other bacteria in untreated periodontitis. J. Dent. Res 2008, 87, 589–593.
  5. Saygun, I.; Kubar, A.; Sahin, S.; Sener, K.; Slots, J. Quantitative analysis of association between herpesviruses and bacterial pathogens in periodontitis. J. Periodontal. Res 2008, 43, 352–359.
  6. Imbronito, A.V.; Okuda, O.S.; Maria de Freitas, N.; Moreira Lotufo, R.F.; Nunes, F.D. Detection of herpesviruses and periodontal pathogens in subgingival plaque of patients with chronic periodontitis, generalized aggressive periodontitis, or gingivitis. J. Periodontol 2008, 79, 2313–2321.
  7. Canabarro, A.; Valle, C.; Farias, M.R.; Santos, F.B.; Lazera, M.; Wanke, B. Association of subgingival colonization of Candida albicans and other yeasts with severity of chronic periodontitis. J. Periodontal. Res 2013, 48, 428–432.
  8. Flemming, H.C.; Wingender, J. The biofilm matrix. Nat. Rev. Microbiol 2010, 8, 623–633.
  9. Lewis, J.P. Metal Uptake in host-pathogen interactions: Role of iron in Porphyromonas gingivalis interactions with host organisms. Periodontol. 2000 2010, 52, 94–116.
  10. McDougald, D.; Rice, S.A.; Barraud, N.; Steinberg, P.D.; Kjelleberg, S. Should we stay or should we go: Mechanisms and ecological consequences for biofilm dispersal. Nat. Rev. Microbiol 2012, 10, 39–50.
  11. Tonetti, M.S.; Imboden, M.A.; Lang, N.P. Neutrophil Migration into the gingival sulcus is associated with transepithelial gradients of interleukin-8 and ICAM-1. J. Periodontol 1998, 69, 1139–1147.
  12. Shapiro, R.S.; Cowen, L.E. Thermal control of microbial development and virulence: Molecular mechanisms of microbial temperature sensing. MBio 2012, 3, doi:10.1128/mBio.00238-12.
  13. Fedi, P.F., Jr; Killoy, W.J. Temperature differences at periodontal sites in health and disease. J. Periodontol. 1992, 63, 24–27.
  14. Percival, R.S.; Marsh, P.D.; Devine, D.A.; Rangarajan, M.; Aduse-Opoku, J.; Shepherd, P.; Curtis, M.A. Effect of temperature on growth, hemagglutination, and protease activity of Porphyromonas gingivalis. Infect. Immun 1999, 67, 1917–1921.
  15. Amano, A.; Fujiwara, T.; Nagata, H.; Kuboniwa, M.; Sharma, A.; Sojar, H.T.; Genco, R.J.; Hamada, S.; Shizukuishi, S. Prophyromonas gingivalis fimbriae mediate coaggregation with Streptococcus oralis through specific domains. J. Dent. Res 1997, 76, 852–857.
  16. Murakami, Y.; Nagata, H.; Amano, A.; Takagaki, M.; Shizukuishi, S.; Tsunemitsu, A.; Aimoto, S. Inhibitory effects of human salivary histatins and lysozyme on coaggregation between Porphyromonas gingivalis and Streptococcus mitis. Infect. Immun 1991, 59, 3284–3286.
  17. Sato, T.; Nakazawa, F. Coaggregation between Prevotella oris and Porphyromonas gingivalis. J. Microbiol. Immunol. Infect. 2012, doi:10.1016/j.jmii.2012.09.005.
  18. Curtis, M.A.; Percival, R.S.; Devine, D.; Darveau, R.P.; Coats, S.R.; Rangarajan, M.; Tarelli, E.; Marsh, P.D. Temperature-dependent modulation of Porphyromonas gingivalis lipid A structure and interaction with the innate host defenses. Infect. Immun 2011, 79, 1187–1193.
  19. Haffajee, A.D.; Socransky, S.S.; Smith, C.; Dibart, S.; Goodson, J.M. Subgingival temperature (III). Relation to microbial counts. J. Clin. Periodontol 1992, 19, 417–422.
  20. Imlay, J.A. Cellular defenses against superoxide and hydrogen peroxide. Annu. Rev. Biochem 2008, 77, 755–776.
  21. Cabiscol, E.; Tamarit, J.; Ros, J. Oxidative stress in bacteria and protein damage by reactive oxygen species. Int. Microbiol 2000, 3, 3–8.
  22. Bradshaw, D.J.; Marsh, P.D.; Watson, G.K.; Allison, C. Role of Fusobacterium nucleatum and coaggregation in anaerobe survival in planktonic and biofilm oral microbial communities during aeration. Infect. Immun 1998, 66, 4729–4732.
  23. Silva, V.L.; Diniz, C.G.; Cara, D.C.; Santos, S.G.; Nicoli, J.R.; Carvalho, M.A.; Farias, L.M. Enhanced pathogenicity of Fusobacterium nucleatum adapted to oxidative stress. Microb. Pathog 2005, 39, 131–138.
  24. Gursoy, U.K.; Pöllänen, M.; Könönen, E.; Uitto, V.J. Biofilm formation enhances the oxygen tolerance and invasiveness of Fusobacterium nucleatum in an oral mucosa culture model. J. Periodontol 2010, 81, 1084–1091.
  25. Steeves, C.H.; Potrykus, J.; Barnett, D.A.; Bearne, S.L. Oxidative stress response in the opportunistic oral pathogen Fusobacterium nucleatum. Proteomics 2011, 11, 2027–2037.
  26. Okano, S.; Shibata, Y.; Shiroza, T.; Abiko, Y. Proteomics-based analysis of a counter-oxidative stress system in Porphyromonas gingivalis. Proteomics 2006, 6, 251–258.
  27. Amano, A.; Sharma, A.; Sojar, H.T.; Kuramitsu, H.K.; Genco, R.J. Effects of temperature stress on expression of fimbriae and superoxide dismutase by Porphyromonas gingivalis. Infect. Immun 1994, 62, 4682–4685.
  28. McKenzie, R.M.; Johnson, N.A.; Aruni, W.; Dou, Y.; Masinde, G.; Fletcher, H.M. Differential response of Porphyromonas gingivalis to varying levels and duration of hydrogen peroxide-induced oxidative stress. Microbiology 2012, 158, 2465–2479.
  29. Gamonal, J.; Acevedo, A.; Bascones, A.; Jorge, O.; Silva, A. Levels of interleukin-1 beta, −8, and −10 and RANTES in gingival crevicular fluid and cell populations in adult periodontitis patients and the effect of periodontal treatment. J. Periodontol 2000, 71, 1535–1545.
  30. Silva, N.; Dutzan, N.; Hernandez, M.; Dezerega, A.; Rivera, O.; Aguillon, J.C.; Aravena, O.; Lastres, P.; Pozo, P.; Vernal, R.; et al. Characterization of progressive periodontal lesions in chronic periodontitis patients: Levels of chemokines, cytokines, matrix metalloproteinase-13, periodontal pathogens and inflammatory cells. J. Clin. Periodontol 2008, 35, 206–214.
  31. Graves, D.T.; Cochran, D. The contribution of interleukin-1 and tumor necrosis factor to periodontal tissue destruction. J. Periodontol 2003, 74, 391–401.
  32. Ishihara, Y.; Nishihara, T.; Maki, E.; Noguchi, T.; Koga, T. Role of interleukin-1 and prostaglandin in in vitro bone resorption induced by Actinobacillus actinomycetemcomitans lipopolysaccharide. J. Periodontal. Res 1991, 26, 155–160.
  33. Cochran, D.L. Inflammation and bone loss in periodontal disease. J. Periodontol 2008, 79, 1569–1576.
  34. Eskan, M.A.; Benakanakere, M.R.; Rose, B.G.; Zhang, P.; Zhao, J.; Stathopoulou, P.; Fujioka, D.; Kinane, D.F. Interleukin-1beta modulates proinflammatory cytokine production in human epithelial cells. Infect. Immun 2008, 76, 2080–2089.
  35. Tanabe, S.; Bodet, C.; Grenier, D. Treponema denticola lipooligosaccharide activates gingival fibroblasts and upregulates inflammatory mediator production. J. Cell. Physiol 2008, 216, 727–731.
  36. Kelk, P.; Claesson, R.; Chen, C.; Sjöstedt, A.; Johansson, A. IL-1beta secretion induced by Aggregatibacter (Actinobacillus) actinomycetemcomitans is mainly caused by the leukotoxin. Int. J. Med. Microbiol 2008, 298, 529–541.
  37. Tanabe, S.I.; Grenier, D. Macrophage tolerance response to Aggregatibacter actinomycetemcomitans lipopolysaccharide induces differential regulation of tumor necrosis factor-alpha, interleukin-1 beta and matrix metalloproteinase 9 secretion. J. Periodontal. Res 2008, 43, 372–377.
  38. Matsuki, Y.; Yamamoto, T.; Hara, K. Interleukin-1 mRNA-expressing macrophages in human chronically inflamed gingival tissues. Am. J. Pathol 1991, 138, 1299–1305.
  39. Hsi, E.D.; Remick, D.G. Monocytes are the major producers of interleukin-1 beta in an ex vivo model of local cytokine production. J. Interferon Cytokine Res 1995, 15, 89–94.
  40. Takeichi, O.; Saito, I.; Tsurumachi, T.; Saito, T.; Moro, I. Human polymorphonuclear leukocytes derived from chronically inflamed tissue express inflammatory cytokines in vivo. Cell. Immunol 1994, 156, 296–309.
  41. Vardar-Sengul, S.; Arora, S.; Baylas, H.; Mercola, D. Expression profile of human gingival fibroblasts induced by interleukin-1beta reveals central role of nuclear factor-kappa b in stabilizing human gingival fibroblasts during inflammation. J. Periodontol 2009, 80, 833–849.
  42. Uchida, Y.; Shiba, H.; Komatsuzawa, H.; Takemoto, T.; Sakata, M.; Fujita, T.; Kawaguchi, H.; Sugai, M.; Kurihara, H. Expression of IL-1 beta and IL-8 by human gingival epithelial cells in response to Actinobacillus actinomycetemcomitans. Cytokine 2001, 14, 152–161.
  43. Dickinson, B.C.; Moffatt, C.E.; Hagerty, D.; Whitmore, S.E.; Brown, T.A.; Graves, D.T.; Lamont, R.J. Interaction of oral bacteria with gingival epithelial cell multilayers. Mol. Oral Microbiol 2011, 26, 210–220.
  44. Stathopoulou, P.G.; Benakanakere, M.R.; Galicia, J.C.; Kinane, D.F. Epithelial cell pro-inflammatory cytokine response differs across dental plaque bacterial species. J. Clin. Periodontol 2010, 37, 24–29.
  45. Umeda, J.E.; Demuth, D.R.; Ando, E.S.; Faveri, M.; Mayer, M.P. Signaling transduction analysis in gingival epithelial cells after infection with Aggregatibacter actinomycetemcomitans. Mol. Oral Microbiol 2012, 27, 23–33.
  46. Peyyala, R.; Kirakodu, S.S.; Novak, K.F.; Ebersole, J.L. Oral microbial biofilm stimulation of epithelial cell responses. Cytokine 2012, 58, 65–72.
  47. Guggenheim, B.; Gmur, R.; Galicia, J.C.; Stathopoulou, P.G.; Benakanakere, M.R.; Meier, A.; Thurnheer, T.; Kinane, D.F. In vitro modeling of host-parasite interactions: The ‘subgingival’ biofilm challenge of primary human epithelial cells. BMC Microbiol. 2009, 9, doi:10.1186/1471-2180-9-280.
  48. Peyyala, R.; Ebersole, J.L. Multispecies biofilms and host responses: “Discriminating the trees from the forest”. Cytokine 2013, 61, 15–25.
  49. Porat, R.; Clark, B.D.; Wolff, S.M.; Dinarello, C.A. Enhancement of growth of virulent strains of Escherichia coli by interleukin-1. Science 1991, 254, 430–432.
  50. Meduri, G.U.; Kanangat, S.; Stefan, J.; Tolley, E.; Schaberg, D. Cytokines IL-1beta, IL-6, and TNF-alpha enhance in vitro growth of bacteria. Am. J. Respir. Crit. Care Med 1999, 160, 961–967.
  51. Stashenko, P.; Fujiyoshi, P.; Obernesser, M.S.; Prostak, L.; Haffajee, A.D.; Socransky, S.S. Levels of interleukin 1 beta in tissue from sites of active periodontal disease. J. Clin. Periodontol 1991, 18, 548–554.
  52. McLaughlin, R.A.; Hoogewerf, A.J. Interleukin-1beta-induced growth enhancement of Staphylococcus aureus occurs in biofilm but not planktonic cultures. Microb. Pathog 2006, 41, 67–79.
  53. Kanangat, S.; Bronze, M.S.; Meduri, G.U.; Postlethwaite, A.; Stentz, F.; Tolley, E.; Schaberg, D. Enhanced extracellular growth of Staphylococcus aureus in the presence of selected linear peptide fragments of human interleukin (IL)-1beta and IL-1 receptor antagonist. J. Infect. Dis 2001, 183, 65–69.
  54. Kanangat, S.; Postlethwaite, A.; Cholera, S.; Williams, L.; Schaberg, D. Modulation of virulence gene expression in Staphylococcus aureus by interleukin-1beta: Novel implications in bacterial pathogenesis. Microbes Infect 2007, 9, 408–415.
  55. Zav’yalov, V.P.; Chernovskaya, T.V.; Navolotskaya, E.V.; Karlyshev, A.V.; MacIntyre, S.; Vasiliev, A.M.; Abramov, V.M. Specific high affinity binding of human interleukin 1 beta by Caf1A usher protein of Yersinia pestis. FEBS Lett 1995, 371, 65–68.
  56. Zav’yalov, V.; Denesyuk, A.; Zav’yalova, G.; Korpela, T. Molecular modeling of the steric structure of the envelope F1 antigen of Yersinia pestis. Immunol. Lett 1995, 45, 19–22.
  57. Wu, L.; Estrada, O.; Zaborina, O.; Bains, M.; Shen, L.; Kohler, J.E.; Patel, N.; Musch, M.W.; Chang, E.B.; Fu, Y.X.; et al. Recognition of host immune activation by Pseudomonas aeruginosa. Science 2005, 309, 774–777.
  58. Diggle, S.P.; Stacey, R.E.; Dodd, C.; Camara, M.; Williams, P.; Winzer, K. The galactophilic lectin, LecA, contributes to biofilm development in Pseudomonas aeruginosa. Environ. Microbiol 2006, 8, 1095–1104.
  59. Cebo, C.; Dambrouck, T.; Maes, E.; Laden, C.; Strecker, G.; Michalski, J.C.; Zanetta, J.P. Recombinant human interleukins IL-1alpha, IL-1beta, IL-4, IL-6, and IL-7 show different and specific calcium-independent carbohydrate-binding properties. J. Biol. Chem 2001, 276, 5685–5691.
  60. Sherblom, A.P.; Decker, J.M.; Muchmore, A.V. The lectin-like interaction between recombinant tumor necrosis factor and uromodulin. J. Biol. Chem 1988, 263, 5418–5424.
  61. Cebo, C.; Vergoten, G.; Zanetta, J.P. Lectin activities of cytokines: Functions and putative carbohydrate-recognition domains. Biochim. Biophys. Acta 2002, 1572, 422–434.
  62. Vergoten, G.; Zanetta, J.P. Structural differences between the putative carbohydrate-recognition domains of human IL-1 alpha, IL-1 beta and IL-1 receptor antagonist obtained by in silico modeling. Glycoconj. J 2007, 24, 183–193.
  63. Mandrell, R.E.; McLaughlin, R.; Aba Kwaik, Y.; Lesse, A.; Yamasaki, R.; Gibson, B.; Spinola, S.M.; Apicella, M.A. Lipooligosaccharides (LOS) of some Haemophilus species mimic human glycosphingolipids, and some LOS are sialylated. Infect. Immun 1992, 60, 1322–1328.
  64. Li, Y.; Sun, M.; Huang, S.; Yu, H.; Chokhawala, H.A.; Thon, V.; Chen, X. The hd0053 gene of Haemophilus ducreyi encodes an α2,3-sialyltransferase. Biochem. Biophys. Res. Commun 2007, 361, 555–560.
  65. Paino, A.; Tuominen, H.; Jääskeläinen, M.; Alanko, J.; Nuutila, J.; Asikainen, S.E.; Pelliniemi, L.J.; Pöllänen, M.T.; Chen, C.; Ihalin, R. Trimeric form of intracellular ATP synthase subunit beta of Aggregatibacter actinomycetemcomitans binds human interleukin-1beta. PLoS One 2011, 6, e18929.
  66. Paino, A.; Lohermaa, E.; Sormunen, R.; Tuominen, H.; Korhonen, J.; Pöllänen, M.T.; Ihalin, R. Interleukin-1β is internalised by viable Aggregatibacter actinomycetemcomitans biofilm and locates to the outer edges of nucleoids. Cytokine 2012, 60, 565–574.
  67. Paino, A.; Ahlstrand, T.; Nuutila, J.; Navickaite, I.; Lahti, M.; Tuominen, H.; Välimaa, H.; Lamminmäki, U.; Pöllänen, M.T.; Ihalin, R. Identification of a novel bacterial outer membrane interleukin-1beta-binding protein from Aggregatibacter actinomycetemcomitans. PLoS One 2013, 8, e70509.
  68. Alcami, A. Viral mimicry of cytokines, chemokines and their receptors. Nat. Rev. Immunol 2003, 3, 36–50.
  69. Treseler, C.B.; Maziarz, R.T.; Levitz, S.M. Biological activity of interleukin-2 bound to Candida albicans. Infect. Immun 1992, 60, 183–188.
  70. Bickel, M.; Munoz, J.L.; Giovannini, P. Acid-base properties of human gingival crevicular fluid. J. Dent. Res 1985, 64, 1218–1220.
  71. Bickel, M.; Cimasoni, G. The pH of human crevicular fluid measured by a new microanalytical technique. J. Periodontal. Res 1985, 20, 35–40.
  72. Eggert, F.M.; Drewell, L.; Bigelow, J.A.; Speck, J.E.; Goldner, M. The pH of gingival crevices and periodontal pockets in children, teenagers and adults. Arch. Oral Biol 1991, 36, 233–238.
  73. Takahashi, N. Acid-neutralizing activity during amino acid fermentation by Porphyromonas gingivalis, Prevotella intermedia and Fusobacterium nucleatum. Oral Microbiol. Immunol 2003, 18, 109–113.
  74. Zilm, P.S.; Rogers, A.H. Co-adhesion and biofilm formation by Fusobacterium nucleatum in response to growth pH. Anaerobe 2007, 13, 146–152.
  75. Zilm, P.S.; Bagley, C.J.; Rogers, A.H.; Milne, I.R.; Gully, N.J. The proteomic profile of Fusobacterium nucleatum is regulated by growth pH. Microbiology 2007, 153, 148–159.
  76. Kapatral, V.; Anderson, I.; Ivanova, N.; Reznik, G.; Los, T.; Lykidis, A.; Bhattacharyya, A.; Bartman, A.; Gardner, W.; Grechkin, G.; et al. Genome sequence and analysis of the oral bacterium Fusobacterium nucleatum strain ATCC 25586. J. Bacteriol 2002, 184, 2005–2018.
  77. Chew, J.; Zilm, P.S.; Fuss, J.M.; Gully, N.J. A proteomic investigation of Fusobacterium nucleatum alkaline-induced biofilms. BMC Microbiol. 2012, 12, doi:10.1186/1471-2180-12-189.
  78. Skar, C.K.; Kruger, P.G.; Bakken, V. Characterisation and subcellular localisation of the GroEL-like and DnaK-like proteins isolated from Fusobacterium nucleatum ATCC 10953. Anaerobe 2003, 9, 305–312.
  79. Oscarsson, J.; Karched, M.; Thay, B.; Chen, C.; Asikainen, S. Proinflammatory effect in whole blood by free soluble bacterial components released from planktonic and biofilm cells. BMC Microbiol. 2008, 8, doi:10.1186/1471-2180-8-206.
  80. Lee, H.R.; Jun, H.K.; Kim, H.D.; Lee, S.H.; Choi, B.K. Fusobacterium nucleatum GroEL induces risk factors of atherosclerosis in human microvascular endothelial cells and apoE(−/−) mice. Mol. Oral Microbiol 2012, 27, 109–123.
  81. Shaniztki, B.; Hurwitz, D.; Smorodinsky, N.; Ganeshkumar, N.; Weiss, E.I. Identification of a Fusobacterium nucleatum PK1594 galactose-binding adhesin which mediates coaggregation with periopathogenic bacteria and hemagglutination. Infect. Immun 1997, 65, 5231–5237.
  82. Liu, P.F.; Shi, W.; Zhu, W.; Smith, J.W.; Hsieh, S.L.; Gallo, R.L.; Huang, C.M. Vaccination targeting surface FomA of Fusobacterium nucleatum against bacterial co-aggregation: implication for treatment of periodontal infection and halitosis. Vaccine 2010, 28, 3496–3505.
  83. Zilm, P.S.; Mira, A.; Bagley, C.J.; Rogers, A.H. Effect of alkaline growth pH on the expression of cell envelope proteins in Fusobacterium nucleatum. Microbiology 2010, 156, 1783–1794.
  84. Schaible, U.E.; Kaufmann, S.H. Iron and microbial infection. Nat. Rev. Microbiol 2004, 2, 946–953.
  85. Shoji, M.; Shibata, Y.; Shiroza, T.; Yukitake, H.; Peng, B.; Chen, Y.Y.; Sato, K.; Naito, M.; Abiko, Y.; Reynolds, E.C.; et al. Characterization of hemin-binding protein 35 (HBP35) in Porphyromonas gingivalis: Its cellular distribution, thioredoxin activity and role in heme utilization. BMC Microbiol. 2010, 10, doi:10.1186/1471-2180-10-152.
  86. Xu, X.; Kolodrubetz, D. Construction and analysis of hemin binding protein mutants in the oral pathogen Treponema denticola. Res. Microbiol 2002, 153, 569–577.
  87. Rhodes, E.R.; Menke, S.; Shoemaker, C.; Tomaras, A.P.; McGillivary, G.; Actis, L.A. Iron acquisition in the dental pathogen Actinobacillus actinomycetemcomitans: What does it use as a source and how does it get this essential metal? Biometals 2007, 20, 365–377.
  88. Al-Qutub, M.N.; Braham, P.H.; Karimi-Naser, L.M.; Liu, X.; Genco, C.A.; Darveau, R.P. Hemin-dependent modulation of the lipid A structure of Porphyromonas gingivalis lipopolysaccharide. Infect. Immun 2006, 74, 4474–4485.
  89. Amarasinghe, J.J.; Scannapieco, F.A.; Haase, E.M. Transcriptional and translational analysis of biofilm determinants of Aggregatibacter actinomycetemcomitans in response to environmental perturbation. Infect. Immun 2009, 77, 2896–2907.
  90. Amarasinghe, J.J.; Connell, T.D.; Scannapieco, F.A.; Haase, E.M. Novel iron-regulated and Fur-regulated small regulatory RNAs in Aggregatibacter actinomycetemcomitans. Mol. Oral Microbiol 2012, 27, 327–349.
  91. Smalley, J.W.; Birss, A.J.; McKee, A.S.; Marsh, P.D. Haemin-restriction influences haemin-binding, haemagglutination and protease activity of cells and extracellular membrane vesicles of Porphyromonas gingivalis W50. FEMS Microbiol. Lett 1991, 69, 63–67.
  92. Hughes, D.T.; Sperandio, V. Inter-kingdom signalling: Communication between bacteria and their hosts. Nat. Rev. Microbiol 2008, 6, 111–120.
  93. Roberts, A.; Matthews, J.B.; Socransky, S.S.; Freestone, P.P.; Williams, P.H.; Chapple, I.L. Stress and the periodontal diseases: Effects of catecholamines on the growth of periodontal bacteria in vitro. Oral Microbiol. Immunol 2002, 17, 296–303.
  94. Socransky, S.S.; Haffajee, A.D.; Cugini, M.A.; Smith, C.; Kent, R.L., Jr. Microbial complexes in subgingival plaque. J. Clin. Periodontol. 1998, 25, 134–144.
  95. Saito, T.; Inagaki, S.; Sakurai, K.; Okuda, K.; Ishihara, K. Exposure of P. gingivalis to noradrenaline reduces bacterial growth and elevates ArgX protease activity. Arch. Oral Biol 2011, 56, 244–250.
  96. Mariotti, A. Sex steroid hormones and cell dynamics in the periodontium. Crit. Rev. Oral Biol. Med 1994, 5, 27–53.
  97. Armitage, G.C. Development of a classification system for periodontal diseases and conditions. Ann. Periodontol 1999, 4, 1–6.
  98. Jonsson, R.; Howland, B.E.; Bowden, G.H. Relationships between periodontal health, salivary steroids, and Bacteroides intermedius in males, pregnant and non-pregnant women. J. Dent. Res 1988, 67, 1062–1069.
  99. Figuero, E.; Carrillo-de-Albornoz, A.; Herrera, D.; Bascones-Martinez, A. Gingival changes during pregnancy: I. Influence of hormonal variations on clinical and immunological parameters. J. Clin. Periodontol 2010, 37, 220–229.
  100. Gursoy, M.; Gursoy, U.K.; Sorsa, T.; Pajukanta, R.; Könönen, E. High salivary estrogen and risk of developing pregnancy gingivitis. J. Periodontol. 2012, doi:10.1902/jop.2012.120512.
  101. Lopatin, D.E.; Kornman, K.S.; Loesche, W.J. Modulation of immunoreactivity to periodontal disease-associated microorganisms during pregnancy. Infect. Immun 1980, 28, 713–718.
  102. Lapp, C.A.; Thomas, M.E.; Lewis, J.B. Modulation by progesterone of interleukin-6 production by gingival fibroblasts. J. Periodontol 1995, 66, 279–284.
  103. Rodriguez, E.; Lopez, R.; Paez, A.; Masso, F.; Montano, L.F. 17Beta-estradiol inhibits the adhesion of leukocytes in TNF-alpha stimulated human endothelial cells by blocking IL-8 and MCP-1 secretion, but not its transcription. Life Sci 2002, 71, 2181–2193.
  104. Shu, L.; Guan, S.M.; Fu, S.M.; Guo, T.; Cao, M.; Ding, Y. Estrogen modulates cytokine expression in human periodontal ligament cells. J. Dent. Res 2008, 87, 142–147.
  105. Jensen, J.; Liljemark, W.; Bloomquist, C. The effect of female sex hormones on subgingival plaque. J. Periodontol 1981, 52, 599–602.
  106. Raber-Durlacher, J.E.; van Steenbergen, T.J.; van der Velden, U.; de Graaff, J.; Abraham-Inpijn, L. Experimental gingivitis during pregnancy and post-partum: Clinical, endocrinological, and microbiological aspects. J. Clin. Periodontol 1994, 21, 549–558.
  107. Carrillo-de-Albornoz, A.; Figuero, E.; Herrera, D.; Bascones-Martinez, A. Gingival changes during pregnancy: II. Influence of hormonal variations on the subgingival biofilm. J. Clin. Periodontol 2010, 37, 230–240.
  108. Kornman, K.S.; Loesche, W.J. Effects of estradiol and progesterone on Bacteroides melaninogenicus and Bacteroides gingivalis. Infect. Immun 1982, 35, 256–263.
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Figure 1. Interactions between periodontal pathogens and host in the subgingival environment.

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Figure 1. Interactions between periodontal pathogens and host in the subgingival environment.
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Table 1. Environmental stimuli affecting periodontal biofilm and bacterial virulence factors.

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Table 1. Environmental stimuli affecting periodontal biofilm and bacterial virulence factors.
StimuliEffectSpeciesReferences
Elevated temperatureProteases ↓Porphyromonas gingivalis[16]
Fimbrial proteins ↓[15]
TLR4 activating lipid-A ↑[18]

Oxidative stressATP production ↓Fusobacterium nucleatum[25]
Chaperones ClpB, DnaK ↑[25]
Heat shock protein HtpG ↑[25]
Transcription repressor HrcA ↑[25]

Oxidative stressChaperones ClpB, DnaK ↑Porphyromonas gingivalis[26]
Heat shock protein HtpG ↑[26]
superoxide dismutase ↑[26]

Inflammatory cytokine IL-1βBiofilm formation ↑Aggregatibacter actinomycetemcomitans[65]
Metabolism ↓[65]

Alkaline pHCo-adhesion ↑Fusobacterium nucleatum[74]
Biofilm formation ↑[74]
Flavodoxin ↑[75]
Glucose storage ↑[77]
Lactate production ↑[77]
Protein synthesis enzymes ↓[77]
Glutamate dehydrogenase ↑[77]
PPI and GroEL ↑[75,77]
FomA adhesion isoforms ↑[77]
ATP synthesis proteins ↓[83]
Butyrate-acetoacetate CoA transferase ↓[83]
Surface antigens Omp IP ↑[83]

Iron-limitationEPS (pgaC) ↑Aggregatibacter actinomycetemcomitans[89]
Fimbrial (tadV) ↑[89]
LPS (rmlB) ↑[89]
Biofilm formation ↑[89]

Iron limitationIron uptake ↑Porphyromonas gingivalis[9]
Iron storage ↓[9]
Oxidative stress response ↓[9]
Biofilm formation ↑[9]
Host cell invasion ↑[9]

High hemin concentrationProteases ↓Porphyromonas gingivalis[91]
Vesicles ↓[91]
TLR4 inactivating lipid A ↑[88]

NoradrenalineGrowth ↓Porphyromonas gingivalis[93]
Arg-gingipain B ↑[95]
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