href="#ulink_b083476d-5d39-5c9e-8dd8-fcac6389a278">Figure 3.
Fig. 3. Simplified diagram of oral biofilm formation.
Novel Treatment Approaches against Oral Biofilms
Oral biofilms are also more tolerant to the action of antimicrobials than planktonic bacteria. For example, a 50-fold MIC (minimal inhibitory concentration) of doxycycline and a 100-fold MIC of metronidazole against planktonic bacteria are required to be active against single species biofilms of P. gingivalis [52]. Still, mechanical removal of an oral biofilm associated with an oral disease is the gold standard in treatment, hence scaling and root planing as an anti-infective and anti-inflammatory therapy of periodontitis [53], or toothbrushing twice a day or more to prevent caries [54]. Still, there is a need for better methods to remove existing biofilms. In recent years new instrumentation treatment options, including certain lasers (e.g., Er:YAG), ultrasonication, or air polishing with special powders, have been introduced for the dentist. These options may combine more efficiency in biofilm removal with less damage of the natural tooth surface and better patient acceptance [55–57].
Novel approaches to overcome the antimicrobial inactivity against biofilms might be the targeted destruction of biofilm matrix molecules or the modification of the oral biofilm. Focusing on the dispersion of the biofilm matrix, enzymes might be of interest to destroy proteins or glucans, but their use is limited by a sensitivity to proteolysis or by limited penetrating ability [58]. A promising target seems to be eDNA; for example, sodium hypochlorite was shown in vitro to destroy eDNA as a component of the biofilm matrix (Fig. 4) [59]. Also, hydrogen peroxide simultaneously degraded the extracellular matrix and killed bacteria within an S. mutans biofilm [60].
Fig. 4. DNA staining of an in vitro-formed multi-species biofilm without (a) and with (b) exposure to 0.1% chlorhexidine digluconate solution, or 1% sodium hypochlorite solution (c) for 1 min.
Modification of the oral biofilm can be achieved by the application of probiotics – viable bacteria which are beneficial. Probiotics were shown to reduce early childhood caries when applied to milk [61] and in periodontal therapy they may help to reduce deep periodontal pockets; however, a long-term colonization within biofilms does not seem to occur [62]. Biofilms can also be modified by applying substances affecting the metabolism of bacteria; arginine, which is utilized by certain oral streptococci, increases the pH in a cariogenic biofilm, thus suppressing mutans streptococci [63].
In conclusion, biofilms represent a major form of microbial life in the oral cavity. Although knowledge has increased enormously over the last decade, more research is needed about the composition of the biofilm matrix in oral diseases and the functionality of the microbiome to develop efficient strategies to combat pathogenic biofilms.
Conflict of Interest Statement
The author has no conflict of interest to declare.
Funding Sources
The author has no funding to declare.
References
1Costerton JW, Geesey GG, Cheng KJ: How bacteria stick. Sci Am 1978;238:86–95.
2O’Toole G, Kaplan HB, Kolter R: Biofilm formation as microbial development. Annu Rev Microbiol 2000;54:49–79.
3Hall MR, McGillicuddy E, Kaplan LJ: Biofilm: basic principles, pathophysiology, and implications for clinicians. Surg Infect 2014;15:1–7.
4Flemming HC, Wingender J, Szewzyk U, Steinberg P, Rice SA, Kjelleberg S: Biofilms: an emergent form of bacterial life. Nat Rev Microbiol 2016;14:563–575.
5Solano C, Echeverz M, Lasa I: Biofilm dispersion and quorum sensing. Curr Opin Microbiol 2014;18:96–104.
6Li YH, Tian X: Quorum sensing and bacterial social interactions in biofilms. Sensors 2012;12:2519–2538.
7Rendueles O, Ghigo JM: Multi-species biofilms: how to avoid unfriendly neighbors. FEMS Microbiol Rev 2012;36:972–989.
8Elias S, Banin E: Multi-species biofilms: living with friendly neighbors. FEMS Microbiol Rev 2012;36:990–1004.
9Dupin C, Tamanai-Shacoori Z, Ehrmann E, Dupont A, Barloy-Hubler F, Bousarghin L, Bonnaure-Mallet M, Jolivet-Gougeon A: Oral Gram-negative anaerobic bacilli as a reservoir of beta-lactam resistance genes facilitating infections with multiresistant bacteria. Int J Antimicrob Agents 2015;45:99–105.
10Maunders E, Welch M: Matrix exopolysaccharides; the sticky side of biofilm formation. FEMS Microbiol Lett 2017;364.
11Jakubovics NS, Shields RC, Rajarajan N, Burgess JG: Life after death: the critical role of extracellular DNA in microbial biofilms. Lett Appl Microbiol 2013;57:467–475.
12Schmeller DS, Loyau A, Bao K, Brack W, Chatzinotas A, De Vleeschouwer F, Friesen J, Gandois L, Hansson SV, Haver M et al: People, pollution and pathogens – global change impacts in mountain freshwater ecosystems. Sci Total Environ 2018;622–623:756–763.
13Wingender J, Flemming HC: Contamination potential of drinking water distribution network biofilms. Water Sci Technol 2004;49(11–12):277–286.
14Soini SM, Koskinen KT, Vilenius MJ, Puhakka JA: Effects of fluid-flow velocity and water quality on planktonic and sessile microbial growth in water hydraulic system. Water Res 2002;36:3812–3820.
15Lienard J, Croxatto A, Gervaix A, Levi Y, Loret JF, Posfay-Barbe