At that time, dental plaque was believed to represent a biomass of bacteria, and the quantity of bacteria was considered to reflect the degree of host response observed. Dental plaque was non-specifically inducing the disease process. In the 1980s, researchers were challenged to find specific pathogens for both caries and periodontal diseases, and it was realized that dental plaque could very well contain specific bacteria responsible for the initiation and promotion of oral diseases. This search for specific pathogens indeed identified groups of micro-organisms with high pathogenic potential and other groups associated with healthy conditions.
In the 1990s and up to the turn of the century, an opportunistic concept of dental plaque gained a lot of attention, and it was realized that the microbial environment substantially influenced the composition of dental plaque, thereby determining its pathogenicity. This paradigm shift in the understanding of the nature of dental plaque culminated in the research of William Costerton and coworkers from the Montana State University in Bozeman, USA, who – at the beginning of the 21st century – provided unequivocal evidence that the bacteria that cause device-related and other chronic infections grow in matrix-enclosed biofilms. The diagnostic and therapeutic strategies that have served in the partial eradication of acute epidemic bacterial diseases have not yielded accurate data or favorable outcomes when applied to these biofilm diseases. The potential benefits of the application of the methods and concepts developed by biofilm science and engineering to the clinical management of infectious diseases are obvious.
Hence, in recent years the term “dental plaque” has been replaced by “oral biofilms.” As biofilms form on all hard, non-shedding surfaces in a fluid system, it is of striking importance to realize that teeth, implants, and prosthetic devices are all affected by biofilm formation.
Biofilms are the most obvious and essential etiologic factors for all oral diseases with the exception of trauma and malignancies. It is, therefore, not surprising to find a chapter dealing with biofilms in each modern dental textbook. However, only few such chapters may deal comprehensively with the issue. The present volume on “biofilms” looks at this interesting structure from various angles. It sheds light on the life in a biofilm beyond the sheer enumeration of single bacterial species. The book is a multi-author production which assures a competent analysis on various cariologic, endodontologic, periodontal, and peri-implant aspects, as well as those of dental unit water lines. The presentation of the life in the biofilms provides a profound understanding of this very interesting and most important structure. The book is recommended for all dental students, graduate students, and biologically oriented dental clinicians.
Niklaus P. Lang
Bern, Switzerland
Published online: December 21, 2020
Eick S (ed): Oral Biofilms. Monogr Oral Sci. Basel, Karger, 2021, vol 29, pp 1–11 (DOI: 10.1159/000510184)
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Sigrun Eick
Department of Periodontology, Laboratory of Oral Microbiology, School of Dental Medicine, University of Bern, Bern, Switzerland
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Abstract
In reality, most microorganisms are not free floating. They exist in biofilms, a community of many of them from the same species or from other genera and attached to surfaces. Microorganisms undergo a transition from free-floating, planktonic microorganisms to a sessile, surface-attached one. Contact with a surface induces changes in gene expression, and a strong attachment of microcolonies occurs only after a few hours. The maturation of a biofilm is associated with matrix formation. The matrix is of importance as it provides stability and protects against environmental insults, it consists of polysaccharides, water, lipids, proteins, and extracellular DNA. Biofilms can be found everywhere – in the environment, in water systems – and they play an important role in medicine and dentistry. In medicine, infections of chronic wounds, of the respiratory tract in cystic fibrosis infections, or when linked with incorporated biomaterial are mostly biofilm associated. In the oral cavity, the most prevalent oral diseases, dental caries, and periodontitis are multi-species biofilm-associated diseases. Although not acting alone, key pathogens drive the development of the microbial shift. Microorganisms metabolize sugar and create an acidic environment where aciduric bacteria (including mutans streptococci) become dominant, which leads to the demineralization of enamel and dentine. Porphyromonas gingivalis causes biofilm dysbiosis in the development of periodontal disease. Biofilm-associated infections are extremely difficult to treat. The matrix serves as a barrier to antimicrobial agents and there are subpopulations of dormant bacteria resistant to antimicrobials requiring metabolically active cells. Approaches to treat biofilm-associated infections include the modification of the biofilm composition, inhibitors of quorum-sensing molecules, or interfering with matrix constituents.
© 2021 S. Karger AG, Basel
Biofilm: A Major Form of Microorganism Living
The term bacterium suggests a free-floating microorganism. Medical microbiology nearly always analyses dispersed single bacteria growing on agar plates or within a liquid to determine their susceptibility to antimicrobials. However, in reality, most microorganisms are not free floating. Instead, they exist together with others from the same species or from other genera attached to surfaces.
Fig. 1. Biofilm formation.
Biofilms are present nearly everywhere. They occur in the environment and they may cause medical problems. Dental plaque as a specialized oral biofilm was investigated relatively early. The following overview deals first with biofilms in general, and then with oral biofilms in particular.
Biofilms in General
The attachment of microorganisms to surfaces is one criterion for a biofilm. Going back in the literature, J.W. Costerton [1] was one of the pioneers in biofilm work. In 1978 he claimed that bacteria are mostly surrounded by extracellular polysaccharides, a “glycocalyx” which may act as a barrier against antibiotics, the bacteria form organized communities. Thus, biofilms can be simply defined as communities that are attached to a surface [2]. They exist as single- and multi-species biofilms [2], with the latter form being the most dominant.
Formation of Biofilms
The biofilm formation is split into several steps, including the initiation, the maturation, the maintenance, and the dispersion of the biofilm [2] (Fig. 1). Microorganisms undergo a transition from a free-floating, planktonic microorganism to a sessile, surface-attached one. They must be able to attach to surfaces, to move on them, and to form a three-dimensional structure [2].
Environmental signals such as pH, nutrients, temperature, oxygen, and others trigger the early attachment of microorganisms to surfaces [2]. In that process, many bacterial structures, like pili or lipopolysaccharides, are involved [2].