Adherence, accumulation, and cell division of a natural adherent bacterial population

Bacterial Adhesion to Natural and Synthetic Fibre-Forming Polymers: Influence of Material Properties

Polymer-based textiles have a major impact on human well-being, as they provide the desired functional protection and aesthetic comfort when worn. However, natural and synthetic polymer-based textiles can also pose serious health risks, as they are surfaces that allow the adhesion of various bacteria, including pathogenic bacteria. To minimise these problems, antibacterial chemical treatments are generally applicable in the case of polymer-based textiles. However, to avoid the use of potentially toxic chemicals, sustainable approaches require the customised design of non-adhesive polymer-based textiles, considering their chemical, physicochemical, constructional, and textural properties. Before designing, several articles are required to gain sufficient knowledge of the described object. Despite the urgent need to combat bacteria (on polymer-based textiles), which pose a serious global health risk, only a few review articles have been published that address bacterial adhesion in the context of superhydrophobic and antibacterial textile materials, while only one review article holistically addresses the textile factors and their influence on this phenomenon. The aim of this review article is to expand the insufficient knowledge about bacterial adhesion to polymer-based textiles on the basis of theoretical findings and real examples through a high degree of structuring, simplification, holistic consideration, and visualization. Therefore, this review provides an insight into the mechanisms involved in bacterial adhesion and a comprehensive overview of the influence of different textile factors, such as chemical composition, hydrophilicity/hydrophobicity, surface charge, surface free energy, roughness, and porosity, on bacterial adhesion. To emphasise the importance of the synergistic effect of the combined textile factors, examples of the influence of hydrophilicity/hydrophobicity in combination with surface charge, surface roughness, and porosity are discussed. From the review, it can be concluded that the combination of hydrophilicity/hydrophobicity and the surface charge of textile fibres and bacteria is crucial for bacterial adhesion, with roughness and porosity being the most important factors among the constructive and textural properties of polymer-based textiles.

Synergistic Effects of Streptococcal Glucosyltransferases on Adhesive Biofilm Formation

Glucosyltransferases (GTF)-I and GTF-SI of Streptococcus mutans synthesize water-insoluble and both water-soluble and -insoluble glucans, respectively, and play essential roles in the sucrose-dependent adhesion of the organism to tooth surfaces. To examine the interactions of different GTFs on artificial biofilm formed by S. mutans and other oral streptococci, we generated GTF-I- and GTF-SI-hyperproducing isogenic mutant strains. Transformant B42-21, which hyperexpressed GTF-SI, exhibited firm adhesion in the presence of sucrose, whereas transformant B42-10, which hyperexpressed GTF-I, failed to exhibit firm adhesion. Furthermore, co-culture of transformant B42-21 with water-soluble glucan-synthesizing Streptococcus sanguinis yielded firm adhesion, while the addition of dextran T10 to B42-21 growing culture had no effect on adhesion. These findings suggest that GTF-SI has a strong effect on sucrose-dependent adhesion and is essential for biofilm formation on smooth surfaces, in cooperation with water-soluble glucans synthesized de novo by oral streptococci that inherently lack cell adhesion ability.

Difference in initial dental biofilm accumulation between night and day

OBJECTIVE

The study of initial microbial colonization on dental surfaces is a field of intensive research because of the aetiological role of biofilms in oral diseases. Most previous studies of de novo accumulation and composition of dental biofilms in vivo do not differentiate between biofilms formed during day and night. This study hypothesized that there is a diurnal variation in the rate of accumulation of bacteria on solid surfaces in the oral cavity.

MATERIALS AND METHODS

In situ biofilm from healthy individuals was collected for 12 h during day and night, respectively, subjected to fluorescent in situ hybridization and visualized using confocal laser scanning microscopy.

RESULTS

Analysis of the biofilms using stereological methods and digital image analysis revealed a consistent statistically significant difference between both the total number of bacteria and the biovolume in the two 12-h groups (p = 0.012), with the highest accumulation of bacteria during daytime (a factor of 8.8 and 6.1 higher, respectively). Hybridization with probes specific for streptococci and Actinomyces naeslundii indicated a higher proportion of streptococci in biofilms grown during daytime as compared to night-time. No differences could be observed for A. naeslundii. The degree of microbial coverage and the bacterial composition varied considerably between different individuals.

CONCLUSION

The data provide firm evidence that initial biofilm formation decreases during the night, which may reflect differences in the availability of salivary nutrients. This finding is of significant importance when studying population dynamics during experimental dental biofilm formation.

Actinomyces naeslundii in initial dental biofilm formation

The combined use of confocal laser scanning microscopy (CLSM) and fluorescent in situ hybridization (FISH) offers new opportunities for analysis of the spatial relationships and temporal changes of specific members of the microbiota of intact dental biofilms. The purpose of this study was to analyse the patterns of colonization and population dynamics of Actinomyces naeslundii compared to streptococci and other bacteria during the initial 48 h of biofilm formation in the oral cavity. Biofilms developed on standardized glass slabs mounted in intra-oral appliances worn by ten individuals for 6, 12, 24 and 48 h. The biofilms were subsequently labelled with probes against A. naeslundii (ACT476), streptococci (STR405) or all bacteria (EUB338), and were analysed by CLSM. Labelled bacteria were quantified by stereological tools. The results showed a notable increase in the number of streptococci and A. naeslundii over time, with a tendency towards a slower growth rate for A. naeslundii compared with streptococci. A. naeslundii was located mainly in the inner part of the multilayered biofilm, indicating that it is one of the species that attaches directly to the acquired pellicle. The participation of A. naeslundii in the initial stages of dental biofilm formation may have important ecological consequences.

Mutational analysis of the adcCBA genes in Streptococcus gordonii biofilm formation

Streptococcus gordonii, a primary colonizer, is part of the pioneer biofilm consortium that initiates dental plaque development on tooth surfaces. An insertion of Tn917-lac transposon into the adcR gene produced a biofilm-defective phenotype. S. gordonii adcR is a regulatory gene and is part of an operon (adc) that includes three other genes, adcCBA. AdcC contains a putative consensus-binding site for adenosine triphosphate, AdcB is a putative hydrophobic membrane protein, and AdcA is a putative lipoprotein permease. Mutants were constructed by insertional inactivation in each of the three adcCBA genes and their effects on biofilm formation examined. The adcC::spec(R) and adcB::spec(R) mutations displayed a biofilm-defective phenotype, whereas the adcA::spec(R) mutant was biofilm-positive in a static polystyrene microtiter plate biofilm assay. All three mutants formed poor biofilms in a flow-cell system and were competence-defective, suggesting the adc operon plays an important role in S. gordonii biofilm formation and competence.

A quorum-sensing signaling system essential for genetic competence in Streptococcus mutans is involved in biofilm formation

In a previous study, a quorum-sensing signaling system essential for genetic competence in Streptococcus mutans was identified, characterized, and found to function optimally in biofilms (Li et al., J. Bacteriol. 183:897-908, 2001). Here, we demonstrate that this system also plays a role in the ability of S. mutans to initiate biofilm formation. To test this hypothesis, S. mutans wild-type strain NG8 and its knockout mutants defective in comC, comD, comE, and comX, as well as a comCDE deletion mutant, were assayed for their ability to initiate biofilm formation. The spatial distribution and architecture of the biofilms were examined by scanning electron microscopy and confocal scanning laser microscopy. The results showed that inactivation of any of the individual genes under study resulted in the formation of an abnormal biofilm. The comC mutant, unable to produce or secrete a competence-stimulating peptide (CSP), formed biofilms with altered architecture, whereas the comD and comE mutants, which were defective in sensing and responding to the CSP, formed biofilms with reduced biomass. Exogenous addition of the CSP and complementation with a plasmid containing the wild-type comC gene into the cultures restored the wild-type biofilm architecture of comC mutants but showed no effect on the comD, comE, or comX mutant biofilms. The fact that biofilms formed by comC mutants differed from the comD, comE, and comX mutant biofilms suggested that multiple signal transduction pathways were affected by CSP. Addition of synthetic CSP into the culture medium or introduction of the wild-type comC gene on a shuttle vector into the comCDE deletion mutant partially restored the wild-type biofilm architecture and further supported this idea. We conclude that the quorum-sensing signaling system essential for genetic competence in S. mutans is important for the formation of biofilms by this gram-positive organism.

Preventive strategies and supportive treatment

There is a preponderance of evidence in the literature that periodontal and other oral diseases, such as caries, can be treated and controlled by thorough mechanical plaque removal by the patient, the use of antimicrobial agents and antibiotics when necessary, and participation with the therapist in a well monitored, long-range program of supportive periodontal therapy. Recent evidence suggests that the control and prevention of oral disease, especially periodontitis, is especially important for patients with various systemic conditions that can be impacted by oral infections. It is far better for patients and therapists to practice primary and even secondary prevention with effective plaque control and regular, consistent supportive periodontal therapy, than having to rely on tertiary prevention for disease that has progressed to a level that requires costly treatment, is time-consuming and carries a greater risk of morbidity.

Retrieval of biofilms from the oral cavity

With the use of the removable stents or bonded enamel piece models with or without a continuous bacterial layer, many in vitro or in vivo studies can be initiated. For example, studies on salivary pellicle formation, surface characteristics of biomaterials as they affect plaque development, antiplaque agents, the dynamics of adhesion of bacteria, interspecies adhesion of bacteria, the colonization of bacteria, the dynamics of bacterial growth in vivo, and the succession of growth in older supragingival plaques can be carried out.

Ultrastructural analysis of structural framework in dental plaque developing on synthetic carbonate apatite applied to human tooth surfaces

This study focused on determining the structural framework by oral microbiota in supragingival plaque on a carbonate apatite film applied to human tooth surfaces. The sequential phases of plaque formation over a 3-wk period were found to be equivalent to those previously reported for natural tooth surfaces. Scanning electron microscopy of specimens prepared by vertical sectioning demonstrated the organization of two types of framework between certain genera of initial and secondary colonizers in the pre- and post-organization phases, respectively. The initial colonizers in the pre-organization phase were of a coccoid type, while colonizers in the post-organization phase were of a bacillary type. Secondary colonizers, filamentous cells, were common to both frameworks. Transmission electron microscopy using freeze-substitution and immunohistochemistry demonstrated two types of coaggregation, fibril- and saliva-mediated modes, among the plaque microbiota. Coaggregation between microbiota, which organized the framework, showed a tendency to occur in the fibril-mediated mode, and the filamentous secondary colonizers were characterized by inducing multigeneric coaggregation. The present findings indicate that a structural framework and specific cells to form this framework are essential for plaque formation.

Biofilm formation as microbial development

Biofilms can be defined as communities of microorganisms attached to a surface. It is clear that microorganisms undergo profound changes during their transition from planktonic (free-swimming) organisms to cells that are part of a complex, surface-attached community. These changes are reflected in the new phenotypic characteristics developed by biofilm bacteria and occur in response to a variety of environmental signals. Recent genetic and molecular approaches used to study bacterial and fungal biofilms have identified genes and regulatory circuits important for initial cell-surface interactions, biofilm maturation, and the return of biofilm microorganisms to a planktonic mode of growth. Studies to date suggest that the planktonic-biofilm transition is a complex and highly regulated process. The results reviewed in this article indicate that the formation of biofilms serves as a new model system for the study of microbial development.

Oral microbial communities: biofilms, interactions, and genetic systems

Oral microbial-plaque communities are biofilms composed of numerous genetically distinct types of bacteria that live in close juxtaposition on host surfaces. These bacteria communicate through physical interactions called coaggregation and coadhesion, as well as other physiological and metabolic interactions. Streptococci and actinomyces are the major initial colonizers of the tooth surface, and the interactions between them and their substrata help establish the early biofilm community. Fusobacteria play a central role as physical bridges that mediate coaggregation of cells and as physiological bridges that promote anaerobic microenvironments which protect coaggregating strict anaerobes in an aerobic atmosphere. New technologies for investigating bacterial populations with 16S rDNA probes have uncovered previously uncultured bacteria and have offered an approach to in situ examination of the spatial arrangement of the participant cells in oral-plaque biofilms. Flow cells with saliva-coated surfaces are particularly useful for studies of biofilm formation and observation. The predicted sequential nature of colonization of the tooth surface by members of different genera can be investigated by using these new technologies and imaging the cells in situ with confocal scanning laser microscopy. Members of at least seven genera now can be subjected to genetic studies owing to the discovery of gene-transfer systems in these genera. Identification of contact-inducible genes in streptococci offers an avenue to explore bacterial responses to their environment and leads the way toward understanding communication among inhabitants of a multispecies biofilm.

Streptococcus gordonii biofilm formation: identification of genes that code for biofilm phenotypes

Viridans streptococci, which include Streptococcus gordonii, are pioneer oral bacteria that initiate dental plaque formation. Sessile bacteria in a biofilm exhibit a mode of growth that is distinct from that of planktonic bacteria. Biofilm formation of S. gordonii Challis was characterized using an in vitro biofilm formation assay on polystyrene surfaces. The same assay was used as a nonbiased method to screen isogenic mutants generated by Tn916 transposon mutagenesis for defective biofilm formation. Biofilms formed optimally when bacteria were grown in a minimal medium under anaerobic conditions. Biofilm formation was affected by changes in pH, osmolarity, and carbohydrate content of the growth media. Eighteen biofilm-defective mutants of S. gordonii Challis were identified based on Southern hybridization with a Tn916-based probe and DNA sequences of the Tn916-flanking regions. Molecular analyses of these mutants showed that some of the genes required for biofilm formation are involved in signal transduction, peptidoglycan biosynthesis, and adhesion. These characteristics are associated with quorum sensing, osmoadaptation, and adhesion functions in oral streptococci. Only nine of the biofilm-defective mutants had defects in genes of known function, suggesting that novel aspects of bacterial physiology may play a part in biofilm formation. Further identification and characterization of biofilm-associated genes will provide insight into the molecular mechanisms of biofilm formation of oral streptococci.

A sensitive method to detect initiation of growth in Streptococcus gordonii using ribosomal RNA operon-reporter gene fusions

A system for studying the early growth response of Streptococcus gordonii to environmental stimuli has been developed. A reporter gene, encoding alpha-amylase, has been integrated into an rRNA operon to monitor changes in cellular physiology associated with the initiation of growth. Two such strains with single integrants have been characterized during the transition from lag phase to exponential growth. Synthesis of the reporter is correlated to growth initiation in both strains, and the reporter enzyme is detectable with sufficient sensitivity. Comparison of the expression profiles of the two rrn operons containing the reporter gene suggests that they are differentially expressed over the course of growth.

Deposition and retention of vital and dead Streptococcus sanguinis cells on glass surfaces in a flow-chamber system

The proportion of vital as compared with dead Streptococcus sanguinis cells attached to glass surfaces was monitored and related to varying proportions of planktonic vital as compared with dead Strep. sanguinis cells. In a flow chamber with six parallel-mounted glass plates, Strep. sanguinis was suspended in pretreated sterile human saliva. Deposition of Strep. sanguinis took place, with a proportion of vital sanguinis streptococci in saliva (%VSs) of 90%, 45% or 22.5%. After exposure times of 30, 60, 90, 120 and 240 min, adherent microorganisms were labelled with two fluorescence stains to differentiate between vital and dead bacteria. Proportions of vital attached streptococci (%VSa) were determined microscopically. Dead bacteria were detected on all glass plates. The %VSa at 30 min and 60 min was significantly lower than the baseline %VSs. During the course of a single run the %VSa frequently increased after either 30, 60 or 90 min without exceeding the %VSs at 4 h. %VSs was the only variable exerting a significant effect on %VSa at 30 and 60 min. It is suggested that during the initial events of microbial attachment the dead rather than vital Strep. sanguinis cells attach preferably to solid surfaces.

Survival of oral bacteria

The global distribution of individual species of oral bacteria demonstrates their ability to survive among their human hosts. Such an ubiquitous existence is the result of efficient transmission of strains and their persistence in the oral environment. Genetic analysis has identified specific clones of pathogenic bacteria causing infection. Presumably, these express virulence-associated characteristics enhancing colonization and survival in their hosts. A similar situation may occur with the oral resident flora, where genetic variants may express specific phenotypic characteristics related to survival. Survival in the mouth is enhanced by dental plaque formation, where persistence is associated with the bacteria's capacity not only to adhere and grow, but also to withstand oxygen, wide fluctuations in pH and carbohydrate concentration, and a diverse array of microbial interactions. Streptococcus mutans has been discussed as a 'model' organism possessing the biochemical flexibility that permits it to persist and dominate the indigenous microflora under conditions of stress.

Cell-cell communication in gram-positive bacteria

In gram-positive bacteria, many important processes are controlled by cell-to-cell communication, which is mediated by extracellular signal molecules produced by the bacteria. Most of these signaling molecules are peptides or modified peptides. Signal processing, in most cases, involves either transduction across the cytoplasmic membrane or import of the signal and subsequent interaction with intracellular effectors. Concentrations of signal in the nanomolar range or below are frequently sufficient for biological activity. The microbial processes controlled by extracellular signaling include the expression of virulence factors, the expression of gene transfer functions, and the production of antibiotics.

Deletions in the carboxyl-terminal region of Streptococcus gordonii glucosyltransferase affect cell-associated enzyme activity and sucrose-associated accumulation of growing cells

The single glucosyltransferase (GTF) of Streptococcus gordonii Challis CH1 makes alpha 1,3- and alpha 1,6-linked glucans from sucrose. The GTF carboxyl-terminal region has six direct repeats thought to be involved in glucan binding. Strains with defined mutations in this region have been described recently (M. M. Vickerman, M. C. Sulavik, P. E. Minick, and D. B. Clewell, Infect. Immun. 64:5117-5128, 1996). Strain CH107 GTF has three internal direct repeats deleted; the 59 carboxyl-terminal amino acids are identical to those of the parental strain. This deletion resulted in decreased enzyme activity but did not affect the amount of cell-associated GTF protein. The GTFs of strains CH2RPE and CH4RPE have six and eight direct repeats, respectively, but are both missing the 14 carboxyl-terminal amino acids. Strain CH2RPE had significantly decreased levels of cell-associated GTF; this decrease was not obviated by the increased number of direct repeats in strain CH4RPE. Thus, the carboxyl-terminal amino acids appeared to influence the amount of cell-associated GTF more than the direct repeats. The qualitative and quantitative differences in the GTFs did not affect the abilities of these strains to accumulate on hydroxyapatite beads in the absence of sucrose. However, when sucrose was added as a substrate for GTF, the mutant strains were unable to accumulate on these surfaces to the same extent as the parent. These differences in sucrose-associated accumulation may be due to changes in the nature of the glucans produced by the different enzymes and/or cohesive interactions between these glucans and the GTF on the surfaces of the growing streptococci.

Growth dynamics in a natural biofilm and its impact on oral disease management

Measurements of the microbial growth dynamics in natural biofilm communities are almost non-existent. In a recent study, the biofilm formation on teeth was examined. A previously unknown active period of bacterial division occurred at a certain density of plaque bacteria on tooth enamel. The density-dependent cell-division phase of plaque formation contributed 90% of the biomass in the first 24 hrs of plaque formation. This suggested that growth was induced by the bacteria. In vitro assays were developed for rapid evaluation of the growth of surface-linked bacteria by the measurement of cellular components associated with growth on a per cell per time basis. Cell-free supernatants (termed START) of media in contact with bacteria were assayed for their effects on DNA synthesis and other cellular components associated with growth. START was found to increase the incorporation of [3H-methyl]-thymidine on a per cell per time basis, when compared with media not in contact with bacteria. Additional in vivo studies and in situ-based models of complex biofilms are needed if all of the mechanisms involved in the rapid accumulation of biofilm bacteria on teeth and other surfaces are to be understood.

Mechanisms of adhesion by oral bacteria

Adherence to a surface is a key element for colonization of the human oral cavity by the more than 500 bacterial taxa recorded from oral samples. Three surfaces are available: teeth, epithelial mucosa, and the nascent surface created as each new bacterial cell binds to existing dental plaque. Oral bacteria exhibit specificity for their respective colonization sites. Such specificity is directed by adhesin-receptor cognate pairs on genetically distinct cells. Colonization is successful when adherent cells grow and metabolically participate in the oral bacterial community. The potential roles of adherence-relevant molecules are discussed in the context of the dynamic nature of the oral econiche.

Human oral microbial ecology and dental caries and periodontal diseases

In the human oral cavity, which is an open growth system, bacteria must first adhere to a surface in order to be able to colonize. Ability to colonize a non-shedding tooth surface is necessary prior to any odontopathic or periodontopathic process. Complex microbe-host relationships occur and must be studied before the commensal-to-pathogenic nature of the human indigenous oral flora can be understood. Medical pathogens, if present in the appropriate host, always produce specific disease. Caries and periodontal diseases are conditional diseases, requiring numbers of certain indigenous species at various sites, particularly the tooth surface. In the case of caries, the condition is related to sugar consumption. Periodontal disease/s may require certain host and environmental conditions, such as local environment or nutritional factors in gingival crevicular fluids. Nonetheless, critical numbers of certain indigenous species must be present in order for these diseases to occur. The aim of this review is to understand the acquisition of the indigenous oral flora and the development of human dental plaque. The role of the salivary pellicle and adherence of indigenous bacteria to it are critical first steps in plaque development. Bacterial interactions with saliva, nutritional factors, growth factors, and microbial physiologic processes are all involved in the overall process of microbial colonization.