Review - ZZI 03/2010
Microbiological and genetical diagnostics for advanced risk profiles
K.–L. Ackermann, N. Reichenbach, H. Lorenz, R. Roessler
Oral biofilms are deposits in the mouth in which various organisms are embedded in a matrix of extracellular polymer substances where they live together synergistically. Disturbances of the “oral” ecosystem are accompanied by proliferation primarily of bacteria that are intolerant or not readily tolerant of oxygen, which can lead to periodontitis or – in the case of implants – periimplantitis. In addition to conventional diagnostic methods, microbiological diagnostics are an important element in the assessment of the disease and in therapeutic decision-making when adjuvant systemic antibiotics are indicated alongside standard therapy. For identification of the causative microorganisms, we now have at our disposal molecular biological techniques as reliable diagnostic methods for the detection of periodontal pathogens. In the majority of cases, bacteria are detected at the DNA level. A key role is played by the genetic component of the clinical picture, which suggests that evaluation of interleukin polymorphism would be a good approach. Findings from recent studies on the detection of active matrix metalloproteinase-8 (aMMP-8) suggest that it is possible to identify – in the sense of expanded PA diagnostics – whether a tissue is biologically healthy or if collagenolytic tissue breakdown is actively occurring.
Keywords: Biofilm; periodontitis; periimplantitis; interleukin-1; aMMP-8; marker bacteria
Oral biofilms are deposits in the mouth in which various organisms are embedded in a matrix of extracellular polymer substances (EPS) where they live together synergistically . As soon as a cleaned surface comes in contact with saliva, an acquired pellicle forms on the enamel, consisting of glycoproteins and antibodies from the saliva. This hydrophilic viscoelastic gel, consisting mainly of filamentous MG1 mucins, forms a protective layer of 0.7–2 µm over the enamel. Both bacteria and tooth surfaces have a negative electric charge. The bacteria overcome these electrostatic forces by means of protons and cations in order to adhere to the tooth surface. Bacterial adhesion to tooth surfaces takes place through specific lectin-like adhesins (proteins that recognize the carbohydrate structure of the pellicle) or hydrophobic adhesins (recognition through receptor molecules), which can likewise overcome electrostatic forces . The pellicle alters the surface energy and the charge of the enamel. Moreover, the pellicle forms the foundation for further colonization of the tooth surface. The majority of bacteria adhering to the pellicle at the forefront are already dead. Further bacteria dock onto this and multiply. Primary colonization is by facultative anaerobic gram-positive bacteria, especially streptococci (Streptococcus sanguis, Streptococcus mitis) and actinomycetes (Actinomycetus viscosus, Actinomycetus naeslundii) .
A matrix of capsule polysaccharides and glycocalix, which is secreted by many streptococci, surrounds the bacterial colony and protects it from external influences and biocides (Fig. 1). Moreover, the extracellular polymer matrix acts as a carrier for nutrients, holds back exo-enzymes and functions as a kind of closed recycling system for cell components and nutrients. The proportion of anaerobic bacteria increases steadily. There are diverse food chains between the different bacteria. The microorganisms are therefore organized into a highly complex biofilm and communicate through a specific circulation system. This information exchange by the bacterial cells is called quorum sensing . The biofilm, in which bacteria can grow into highly organized structures, is 1000 times more resistant to medications and the immune response than in plankton form. One reason for the increased resistance of the bacteria, for example against antibiotics, is the polysaccharide matrix itself, which surrounds the bacteria like a protective film. Diffusion of antibiotics through this matrix is limited so that the minimum inhibitory concentration cannot be reached as easily as when the bacteria are present in plankton form (Table 1). It is also possible that transmission of virulence factors by gene transfer is enabled within the biofilm so that an avirulent microorganism can become virulent or a nonresistant microorganism becomes resistant to an antibiotic. Up to 500 different bacterial species have so far been detected in the subgingival biofilm, though not all of these are equally pathogenic . The most important are: Porphyromonas gingivalis, Tannerella forsythia, Aggregatibacter actinomycetemcomitans, Prevotella intermedia and Prevotella nigrescens.
Disturbances of the “oral” ecosystem are accompanied by proliferation primarily of bacteria that are intolerant or not readily tolerant of oxygen (facultative or strict anaerobes). The result is an infectious disease, namely periodontitis (Table 2) or – in the case of implants – periimplantitis. Influenced by the release of toxins, it leads to damage to the periodontal ligament and can result in total loss of the teeth or implants.
According to Socransky four factors have to come together in order to provoke or maintain periodontal processes: a host with inadequate oral hygiene and thus a favorable local environment, a defective immune system, an increased number of pathogenic bacteria and a reduced number of “nonpathogenic” species of microorganisms. This demonstrates that the bacterial factor plays a crucial part in the development of the disease and has the great advantage of being “measurable” so that it can be utilized for planning therapy [1, 2].