In situ Biofilm Formation by Multi-species Oral Bacteria Under Flowing and Anaerobic Conditions

Unsaturated fatty acid salts remove biofilms on dentures

Candidiasis-causing Candida sp. forms biofilms with various oral bacteria in the dentures of the elderly, making it harder to kill and remove the microorganism due to the extracellular polymeric substances. We found that biofilms on dentures can effectively be removed by immersion in an unsaturated fatty acid salt solution. Using optical coherence tomography to observe the progression of biofilm removal by the fatty acid salt solution, we were able to determine that the removal was accompanied by the production of gaps at the interface between the biofilm and denture resin. Furthermore, microstructural electron microscopy observations and time-of-flight secondary ion mass spectrometry elucidated the site of action, revealing that localization of the fatty acid salt at the biofilm/denture-resin interface is an important factor.

Streptococcus mutans and Actinomyces naeslundii Interaction in Dual-Species Biofilm

The study of bacterial interaction between Streptococcus mutans and Actinomyces naeslundii may disclose important features of biofilm interspecies relationships. The aim of this study was to characterize-with an emphasis on biofilm formation and composition and metabolic activity-single- and dual-species biofilms of S. mutans or A. naeslundii, and to use a drip flow reactor (DFR) to evaluate biofilm stress responses to 0.2% chlorhexidine diacetate (CHX). Single- and dual-species biofilms were grown for 24 h. The following factors were evaluated: cell viability, biomass and total proteins in the extracellular matrix, 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide-"XTT"-reduction and lactic acid production. To evaluate stress response, biofilms were grown in DFR. Biofilms were treated with CHX or 0.9% sodium chloride (NaCl; control). Biofilms were plated for viability assessment. Confocal laser-scanning microscopy (CLSM) was also performed. Data analysis was carried out at 5% significance level. S. mutans viability and lactic acid production in dual-species biofilms were significantly reduced. S. mutans showed a higher resistance to CHX in dual-species biofilms. Total protein content, biomass and XTT reduction showed no significant differences between single- and dual-species biofilms. CLSM images showed the formation of large clusters in dual-species biofilms. In conclusion, dual-species biofilms reduced S. mutans viability and lactic acid production and increased S. mutans' resistance to chlorhexidine.

Characterization of Mixed-Species Biofilm Formed by Vibrio parahaemolyticus and Listeria monocytogenes

Mixed-species biofilms are the predominant form of biofilms found in nature. Research on biofilms have typically concentrated on single species biofilms and this study expands the horizon of biofilm research, where the characterization and dynamic changes of mono and mixed-species biofilms formed by the pathogens, Vibrio parahaemolyticus and Listeria monocytogenes were investigated. Compared to mono-species biofilm, the biomass, bio-volume, and thickness of mixed-species biofilms were significantly lower, which were confirmed using crystal violet staining, confocal laser scanning microscopy and scanning electron microscopy. Further experimental analysis showed these variations might result from the reduction of bacterial numbers, the down-regulation of biofilm-regulated genes and loss of metabolic activity in mixed-species biofilm. In addition, V. parahaemolyticus was located primarily on the surface layers of the mixed-species biofilms thus accruing competitive advantage. This competitive advantage was evidenced in a higher V. parahaemolyticus population density in the mixed-species biofilms. The adhesion to surfaces of the mixed-species biofilms were also reduced due to lower concentrations of extracellular polysaccharide and protein when the structure of the mixed-species was examined using Raman spectral analysis, phenol-sulfuric acid method and Lowry method. Furthermore, the minimum biofilm inhibitory concentration to antibiotics obviously decreased when V. parahaemolyticus co-exited with L. monocytogenes. This study firstly elucidated the interactive behavior in biofilm development of two foodborne pathogens, and future studies for biofilm control and antibiotic therapy should take into account interactions in mixed-species biofilms.

Multispecies biofilm formation by the contaminating microbiota in raw milk

Biofilms can be formed on the surfaces of dairy processing equipment and are a potential source of product contamination. This study evaluated the diversity of multispecies biofilms formed on stainless steel (SS) due to the contaminating microbiota in raw milk. Samples of raw milk were used: one was fresh milk and the other maintained in refrigerated bulk tanks for up to 48 h. The mesophilic aerobic contamination was ∼10⁴ CFU ml^-1 in fresh milk and 10⁶ CFU ml^-1 in bulk milk. SS coupons were kept immersed in the milk at 7 ±2 °C for 10 days, and every two days, the raw milk was changed for samples of the same origin collected on the current day. After incubation for 10 days, sessile cells in the biofilm reached 10⁵ CFU cm^-2 in the presence of fresh milk, and 10⁶ CFU cm^-2 in the presence of bulk milk. The genetic diversity analysis showed that Gammaproteobacteria and Bacilli predominated in the biofilms throughout the incubation of both milk samples and these biofilms showed a reduction in diversity over time. The main classes of bacteria found in these biofilms have representatives of great importance since many of them have spoilage potential.

Multispecies Biofilm Development of Marine Bacteria Implies Complex Relationships Through Competition and Synergy and Modification of Matrix Components

Microbial communities composition is largely shaped by interspecies competition or cooperation in most environments. Ecosystems are made of various dynamic microhabitats where microbial communities interact with each other establishing metabolically interdependent relationships. Very limited information is available on multispecies biofilms and their microhabitats related to natural environments. The objective of this study is to understand how marine bacteria isolated from biofilms in the Mediterranean Sea interact and compete with each other when cultivated in multispecies biofilms. Four strains (Persicivirga mediterranea TC4, Polaribacter sp. TC5, Shewanella sp. TC10 and TC11) with different phenotypical traits and abilities to form a biofilm have been selected from a previous study. Here, the results show that these strains displayed a different capacity to form a biofilm in static versus dynamic conditions where one strain, TC11, was highly susceptible to the flux. These bacteria appeared to be specialized in the secretion of one or two exopolymers. Only TC5 seemed to secrete inhibitory molecule(s) in its supernatant, with a significant effect on TC10. Most of the strains negatively impacted each other, except TC4 and TC10, which presented a synergetic effect in the two and three species biofilms. Interestingly, these two strains produced a newly secreted compound when grown in dual-species versus mono-species biofilms. TC5, which induced a strong inhibition on two of its partners in dual-species biofilms, outfitted the other bacteria in a four-species biofilm. Therefore, understanding how bacteria respond to interspecific interactions should help comprehending the dynamics of bacterial populations in their ecological niches.

Synergistic Interactions in Microbial Biofilms Facilitate the Establishment of Opportunistic Pathogenic Fungi in Household Dishwashers

Biofilms formed on rubber seals in dishwashers harbor diverse microbiota. In this study, we focussed on the microbial composition of bacteria and fungi, isolated from a defined area of one square centimeter of rubber from four domestic dishwashers and assessed their abilities to in vitro multispecies biofilm formation. A total of 80 isolates (64 bacterial and 16 fungal) were analyzed. Multiple combinations of bacterial isolates from each dishwasher were screened for synergistic interactions. 32 out of 140 tested (23%) four-species bacterial combinations displayed consistent synergism leading to an overall increase in biomass, in all experimental trails. Bacterial isolates from two of the four dishwashers generated a high number of synergistically interacting four-species consortia. Network based correlation analyses also showed higher co-occurrence patterns observed between bacterial members in the same two dishwasher samples, indicating cooperative effects. Furthermore, two synergistic four-species bacterial consortia were tested for their abilities to incorporate an opportunistic fungal pathogen, Exophiala dermatitidis and their establishment as biofilms on sterile ethylene propylene diene monomer M-class (EPDM) rubber and polypropylene (PP) surfaces. When the bacterial consortia included E. dermatitidis, the overall cell numbers of both bacteria and fungi increased and a substantial increase in biofilm biomass was observed. These results indicate a novel phenomenon of cross kingdom synergy in biofilm formation and these observations could have potential implications for human health.

Novel multifunctional dental bonding agent for Class-V restorations to inhibit periodontal biofilms

We recently developed a dental bonding agent to bond restorations to teeth using nanoparticles of amorphous calcium phosphate (NACP) for remineralization with rechargeable calcium and phosphate ion release. The objectives of this study were to: (1) incorporate an antibacterial monomer dimethylaminohexadecyl methacrylate (DMAHDM) and a protein-repellent agent 2-methacryloyloxyethyl phosphorylcholine (MPC); and (2) investigate protein adsorption and periodontitis-related biofilms for the first time. A primer, used to prime tooth structures for bonding, was made with pyromellitic glycerol dimethacrylate (PMGDM) and 2-hydroxyethyl methacrylate (HEMA). An adhesive was made with PMGDM, ethoxylated bisphenol A dimethacrylate and HEMA. NACP, MPC and DMAHDM were incorporated. Streptococcus gordonii, Actinomyces naeslundii, Porphyromonas gingivalis, Fusobacterium nucleatum were cultured to form single and multi-species biofilms. Colony-forming units (CFU), live/dead, metabolic activity, and polysaccharide were measured. Adding DMAHDM, MPC and NACP into the bonding agent did not compromise the dentin bond strength (p > 0.1). Bonding agents with 5% MPC reduced protein adsorption to 1/15 that of the control (p < 0.05). Bonding agents with 5% DMAHDM + 5% MPC had much greater reduction in biofilms than DMAHDM or MPC alone (p < 0.05). Biofilm CFU was reduced by 3 to 4 log via DMAHDM + MPC. Metabolic activities and polysaccharide of biofilms were also substantially reduced (p < 0.05). In conclusion, a novel bonding agent was developed for dental restorations with inhibition of biofilms, reducing CFU by 3 to 4 log. Besides remineralizartion and acid-neutralization via NACP to inhibit caries as shown previously, the multifunctional adhesive is promising for root restorations with subgingival margins to suppress periodontal pathogens and protect the periodontium.

Linkages between oral commensal bacteria and atherosclerotic plaques in coronary artery disease patients

Coronary artery disease is an inflammatory disorder characterized by narrowing of coronary arteries due to atherosclerotic plaque formation. To date, the accumulated epidemiological evidence supports an association between oral bacterial diseases and coronary artery disease, but has failed to prove a causal link between the two. Due to the recent surge in microbial identification and analyses techniques, a number of bacteria have been independently found in atherosclerotic plaque samples from coronary artery disease patients. In this study, we present meta-analysis from published studies that have independently investigated the presence of bacteria within atherosclerotic plaque samples in coronary artery disease patients. Data were collated from 63 studies covering 1791 patients spread over a decade. Our analysis confirms the presence of 23 oral commensal bacteria, either individually or in co-existence, within atherosclerotic plaques in patients undergoing carotid endarterectomy, catheter-based atherectomy, or similar procedures. Of these 23 bacteria, 5 (Campylobacter rectus, Porphyromonas gingivalis, Porphyromonas endodontalis, Prevotella intermedia, Prevotella nigrescens) are unique to coronary plaques, while the other 18 are additionally present in non-cardiac organs, and associate with over 30 non-cardiac disorders. We have cataloged the wide spectrum of proteins secreted by above atherosclerotic plaque-associated bacteria, and discuss their possible roles during microbial migration via the bloodstream. We also highlight the prevalence of specific poly-microbial communities within atherosclerotic plaques. This work provides a resource whose immediate implication is the necessity to systematically catalog landscapes of atherosclerotic plaque-associated oral commensal bacteria in human patient populations.

A review of bacterial populations in the mouth and in diseased arteries will help research into the role of bacteria in heart disease. Amit Sharma and colleagues at the International Centre for Genetic Engineering and Biotechnology, with co-workers at the All India Institute of Medical Sciences, both in New Delhi, India, analyzed 63 studies covering 1791 patients spread over a decade. They summarize evidence of 23 types of oral bacteria that are also found in atherosclerotic plaques in artery walls. The review also cataloged the proteins secreted by the bacteria and discussed possible involvement of these proteins in the migration of bacteria through the bloodstream. Full genetic details are available for 19 of the 23 bacterial species, which should greatly assist further investigations into the significance of bacteria in the onset of heart disease.

How to Study Biofilms after Microbial Colonization of Materials Used in Orthopaedic Implants

Over the years, various techniques have been proposed for the quantitative evaluation of microbial biofilms. Spectrophotometry after crystal violet staining is a widespread method for biofilm evaluation, but several data indicate that it does not guarantee a good specificity, although it is rather easy to use and cost saving. Confocal laser microscopy is one of the most sensitive and specific tools to study biofilms, and it is largely used for research. However, in some cases, no quantitative measurement of the matrix thickness or of the amount of embedded microorganisms has been performed, due to limitation in availability of dedicated software. For this reason, we have developed a protocol to evaluate the microbial biofilm formed on sandblasted titanium used for orthopaedic implants, that allows measurement of biomass volume and the amount of included cells. Results indicate good reproducibility in terms of measurement of biomass and microbial cells. Moreover, this protocol has proved to be applicable for evaluation of the efficacy of different anti-biofilm treatments used in the orthopaedic setting. Summing up, the protocol here described is a valid and inexpensive method for the study of microbial biofilm on prosthetic implant materials.

Continuous live cell imaging of cellulose attachment by microbes under anaerobic and thermophilic conditions using confocal microscopy

Live cell imaging methods provide important insights into the dynamics of cellular processes that cannot be derived easily from population-averaged datasets. In the bioenergy field, much research is focused on fermentation of cellulosic biomass by thermophilic microbes to produce biofuels; however, little effort is dedicated to the development of imaging tools to monitor this dynamic biological process. This is, in part, due to the experimental challenges of imaging cells under both anaerobic and thermophilic conditions. Here an imaging system is described that integrates confocal microscopy, a flow cell device, and a lipophilic dye to visualize cells. Solutions to technical obstacles regarding suitable fluorescent markers, photodamage during imaging, and maintenance of environmental conditions during imaging are presented. This system was utilized to observe cellulose colonization by Clostridium thermocellum under anaerobic conditions at 60 degrees C. This method enables live cell imaging of bacterial growth under anaerobic and thermophilic conditions and should be widely applicable to visualizing different cell types or processes in real time.

Multi-species biofilms: living with friendly neighbors

Our knowledge regarding the nature and development of microbial biofilms has grown significantly since the first report of these communities by Antonie van Leeuwenhoek in the late 1600s. Nevertheless, most biofilm studies examine mono-species cultures, whereas nearly all biofilm communities in nature comprise a variety of microorganisms. The species that constitute a mixed biofilm and the interactions between these microorganisms critically influence the development and shape of the community. In this review, we focus on interactions occurring within a multi-species biofilm and their effects on the nature of the mixed community. In general, interspecies interactions involve communication, typically via quorum sensing, and metabolic cooperation or competition. Interactions among species within a biofilm can be antagonistic, such as competition over nutrients and growth inhibition, or synergistic. The latter can result in the development of several beneficial phenotypes. These include the promotion of biofilm formation by co-aggregation, metabolic cooperation where one species utilizes a metabolite produced by a neighboring species, and increased resistance to antibiotics or host immune responses compared to the mono-species biofilms. These beneficial interactions in mixed biofilms have important environmental, industrial, and clinical implications. The latter, for example, impacts the course and treatment of biofilm-related infections, such as those manifested in the lungs of cystic fibrosis patients.

The impact of antimicrobial photodynamic therapy in an artificial biofilm model

The susceptibility of bacterial cultures in biofilm formations is important for a variety of clinical treatment procedures. Therefore, the aim of the study was to assess the impact of laser-induced antimicrobial photodynamic therapy on the viability of Streptococcus mutans cells employing an artificial biofilm model. Using sterile chambered coverglasses, a salivary pellicle layer was formed in 40 chambers. Streptococcus mutans cells were inoculated in a sterile culture medium. Employing a live/dead bacterial viability kit, bacteria with intact cell membranes stained fluorescent green. Each pellicle-coated test chamber was filled with 0.7 ml of the bacterial suspension and analysed using a confocal laser scanning microscope within a layer of 10 μm at intervals of 1 μm from the pellicle layer. Phenothiazine chloride was used as a photosensitizer in all 40 test chambers. A diode laser (wavelength 660 nm, output power 100 mW) was used to irradiated 20 chambers for 2 min. Fluorescence values in the test chambers after laser irradiation (median 2.1 U, range 0.4-3.4 U) were significantly lower than baseline values after adding the photosensitizer (median 3.6 U, range 1.1-9.0; p < 0.05). The non-irradiated control chambers showed no change in fluorescence at the end of an additional photosensitizer residence time of 2 min without laser irradiation (median 1.9 U, range 0.7-3.6; median 1.9 U, range 0.8-6.0, respectively; p > 0.05). The present study indicated that laser irradiation is an essential part of antimicrobial photodynamic therapy to reduce bacteria within a layer of 10 μm. Further studies are needed to evaluate the maximum biofilm thickness that still allows a toxic effect on microorganisms.

Selective killing of Aggregatibacter actinomycetemcomitans by ciprofloxacin during development of a dual species biofilm with Streptococcus sanguinis

OBJECTIVES

Periodontal disease is associated with a pathogen-induced transition to a chronic destructive inflammatory response. Since commensals may either passively or actively contribute to immune homeostasis, therapies aimed at selectively reducing the competitive advantage of pathogens may be effective supplements to traditional methods. We developed an in vitro system to grow biofilms composed of the pathogen (Aggregatibacter actinomycetemcomitans) and the commensal (Streptococcus sanguinis). We used the biofilm model to determine the feasibility of selectively killing the pathogen using the fluoroquinolone, ciprofloxacin.

DESIGN

Biofilms were exposed to relevant ciprofloxacin doses during the first 24h of development, with subsequent removal of the ciprofloxacin for a 24h period. Biofilm growth was assessed by confocal laser scanning microscopy, crystal violet staining and DNA abundance.

RESULTS

Exposure to 0.01mg/L or 0.5mg/L ciprofloxacin significantly reduced the microcolony size and cell surface density of A. actinomycetemcomitans in the dual species biofilm over a 24h period whilst allowing uninhibited S. sanguinis biofilm formation. A. actinomycetemcomitans biofilm development was insignificant over a subsequent 24h period after removal of the ciprofloxacin indicating that A. actinomycetemcomitans cells were killed.

CONCLUSIONS

A. actinomycetemcomitans residing in a dual species biofilm with the commensal, S. sanguinis can be selectively killed, or at least rendered metabolically inactive, by treatment with ciprofloxacin. The dual species biofilm model will be a useful tool for designing in vivo studies to determine the efficacy of selective killing agents as an adjunct treatment of localized aggressive forms of periodontal disease.

Oral biofilms: emerging concepts in microbial ecology

Oral biofilms develop under a range of different conditions and different environments. This review will discuss emerging concepts in microbial ecology and how they relate to oral biofilm development and the treatment of oral diseases. Clues to how oral biofilms develop may lie in other complex systems, such as interactions between host and gut microbiota, and even in factors that affect biofilm development on leaf surfaces. Most of the conditions under which oral biofilms develop are tightly linked to the overall health and biology of the host. Advances in molecular techniques have led to a greater appreciation of the diversity of human microbiota, the extent of interactions with the human host, and how that relates to inter-individual variation. As a consequence, plaque development may no longer be thought of as a generic process, but rather as a highly individualized process, which has ramifications for the treatment of the diseases it causes.

Antibacterial coatings for medical devices based on glass polyalkenoate cement chemistry

A biofilm is an accumulation of micro-organisms and their extracellular products forming a structured community on a surface. Biofilm formation on medical devices has severe health consequences as bacteria growing in this lifestyle are tolerant to both host defense mechanisms and antibiotic therapies. However, silver and zinc ions inhibit the attachment and proliferation of immature biofilms. The objective of this study is to evaluate whether it is possible to produce silver and zinc-containing glass polyalkenoate cement (GPC) coatings for medical devices that have antibacterial activity and which may therefore inhibit biofilm formation on a material surface. Two silver and zinc-containing GPC coatings (A and B) were synthesised and coated onto Ti6Al4V discs. Their handling properties were characterised and atomic absorption spectrometery was employed to determine zinc and silver ion release with coating maturation up to 30 days. The antibacterial properties of the coatings were also evaluated against Staphylococcus aureus and a clinical isolate of Pseudomonas aeruginosa using an agar diffusion assay method. The majority of the zinc and silver ions were released within the first 24 h; both coatings exhibited antibacterial effect against the two bacterial strains, but the effect was more intense for B which contained more silver and less zinc than A. Both coatings produced clear zones of inhibition with each of the two organisms tested. In this assay, Ps. aeruginosa was more sensitive than S. aureus. The diameters of these zones were reduced after the coating had been immersed in water for varying periods due to the resultant effect on ion release.

Aggregatibacter actinomycetemcomitans serotype f O-polysaccharide mediates coaggregation with Fusobacterium nucleatum

BACKGROUND/AIMS

Intergeneric bacterial coaggregation may play an important role in plaque development.

METHODS

In this study we investigated the coaggregation reaction between two periodontal pathogens, Aggregatibacter actinomycetemcomitans and Fusobacterium nucleatum.

RESULTS

Previous studies showed that A. actinomycetemcomitans serotype b strains coaggregate with F. nucleatum strain PK1594, and that A. actinomycetemcomitans serotype b O-polysaccharide (O-PS) is the receptor responsible for coaggregation between A. actinomycetemcomitans and F. nucleatum. A. actinomycetemcomitans serotype f O-PS has been shown to be structurally and antigenically related to serotype b O-PS. In the present study we show that A. actinomycetemcomitans strain CU1060N, a serotype f strain, also coaggregated with F. nucleatum PK1594. Like coaggregation between serotype b strains and F. nucleatum, coaggregation between CU1060N and F. nucleatum was inhibited by galactose. An O-PS mutant of CU1060N failed to coaggregate with F. nucleatum.

CONCLUSION

We concluded that A. actinomycetemcomitans serotype f O-PS, like serotype b O-PS, mediates coaggregation between A. actinomycetemcomitans and fusobacteria.

A fluorescence assay to determine the viable biomass of microcosm dental plaque biofilms

Dental plaque bacteria form complex and robust cell aggregates which cannot be counted accurately using epifluorescence microscopy. This causes a significant problem for quantifying their viability. The aim of the investigation was to develop a fluorescence assay to quantify the viable biomass of dental plaque biofilms. Using an artificial mouth system, microcosm plaques were grown under a range of fluoride and mineralizing conditions, and were treated with the oral antiseptics chlorhexidine (CHX) and Listerine. Plaques were harvested, made into suspension and stained in microtitre plates with a di-chromatic fluorescent stain (Live/Dead BacLight). The percentage of viable biomass was calculated from the regression data generated from a viability standard. The standard was constructed using different proportions of viable (green fluorescence) and non-viable (red fluorescence) plaque bacteria, and growth conditions for optimizing green fluorescence were investigated. The results from the assay showed that fluoride at 1000 and 3000 ppm promoted plaque viability by at least 15%, from approximately 45 to 60%, and at 5000 ppm to approximately 87% (P<0.05). Plaques treated with Listerine and CHX from d 0 yielded insufficient biomass to be tested for viability, however 14 d post-treatment, viability was comparable to untreated plaques (approximately 55%, P>0.05). Treatment with Listerine and CHX from d 3 reduced biomass but not viability. Development of this assay enabled viability of plaque bacteria which cannot be resolved with epifluorescence microscopy to be evaluated. It offers a rapid alternative to epifluorescence microscopy and could be applied to nonoral bacteria.

Microbial colonization and competition on the marine alga Ulva australis

Pseudalteromonas tunicata and Roseobacter gallaeciensis are biofilm-forming marine bacteria that are often found in association with the surface of the green alga Ulva australis. They are thought to benefit the plant host by producing inhibitory compounds that are active against common fouling organisms. We investigated factors that influence the ability of P. tunicata and R. gallaeciensis to attach to and colonize the plant surface and also the competitive interactions that occur between these organisms and other isolates from U. australis during biofilm formation on the plant surface. A surprisingly high number of P. tunicata cells, at least 10(8) cells ml(-1), were required for colonization and establishment of a population of cells that persists on axenic surfaces of U. australis. Factors that enhanced colonization of P. tunicata included inoculation in the dark and pregrowth of inocula in medium containing cellobiose as the sole carbon source (cellulose is a major surface polymer of U. australis). It was also found that P. tunicata requires the presence of a mixed microbial community to colonize effectively. In contrast, R. gallaeciensis effectively colonized the plant surface under all conditions tested. Studies of competitive interactions on the plant surface revealed that P. tunicata was numerically dominant compared with all other bacterial isolates tested (except R. gallaeciensis), and this dominance was linked to production of the antibacterial protein AlpP. Generally, P. tunicata was able to coexist with competing strains, and each strain existed as microcolonies in spatially segregated regions of the plant. R. gallaeciensis was numerically dominant compared with all strains tested and was able to invade and disperse preestablished biofilms. This study highlighted the fact that microbial colonization of U. australis surfaces is a dynamic process and demonstrated the differences in colonization strategies exhibited by the epiphytic bacteria P. tunicata and R. gallaeciensis.

Biofilms, a new approach to the microbiology of dental plaque

Dental plaque has the properties of a biofilm, similar to other biofilms found in the body and the environment. Modern molecular biological techniques have identified about 1000 different bacterial species in the dental biofilm, twice as many as can be cultured. Oral biofilms are very heterogeneous in structure. Dense mushroom-like structures originate from the enamel surface, interspersed with bacteria-free channels used as diffusion pathways. The channels are probably filled with an extracellular polysaccharide (EPS) matrix produced by the bacteria. Bacteria in biofilms communicate through signaling molecules, and use this "quorum-sensing" system to optimize their virulence factors and survival. Bacteria in a biofilm have a physiology different from that of planktonic cells. They generally live under nutrient limitation and often in a dormant state. Such "sleepy" bacteria respond differently to antibiotics and antimicrobials, because these agents were generally selected in experiments with metabolically active bacteria. This is one of the explanations as to why antibiotics and antimicrobials are not as successful in the clinic as could be expected from laboratory studies. In addition, it has been found that many therapeutic agents bind to the biofilm EPS matrix before they even reach the bacteria, and are thereby inactivated. Taken together, these fundings highlight why the study of bacteria in the oral cavity is now taken on by studying the biofilms rather than individual species.

Microbubble-induced detachment of coadhering oral bacteria from salivary pellicles

The presence and maturity of the salivary pellicle influences microbial adhesion and its tenacity in the oral cavity, posing a challenge to different plaque-control systems. Some plaque-control systems rely on surface-tension forces arising from passing microbubbles sprayed over the pellicle. Passage of such bubbles is accompanied by a high fluid flow, but systematic studies are lacking on the contribution of fluid flow vs. microbubbles towards plaque removal. Therefore, the aim of this study was to determine the detachment efficacy of laminar fluid flow (wall shear rates 11,000-16,000 s(-1)), with and without microbubbles, towards the detachment of Actinomyces naeslundii T14V-J1 and Streptococcus oralis J22, and their coadhering aggregates, from salivary pellicles formed over 2 h or 16 h from reconstituted human whole saliva. Microbubbles in a fluid flow were more efficient at inducing single bacterial detachment, resulting in almost complete (97%) removal for S. oralis J22 and a 15-fold increase in A. naeslundii T14V-J1 removal as compared to the detachment caused by fluid flow alone. A. naeslundii was more difficult to remove and apparently formed the strongest bonds with high-molecular-weight proteins in 16-h pellicles. The detachment of coaggregates after 2 min left a substantial amount of adhered bacterial mass, including more than 60% of singly attached A. naeslundii on the pellicle surface, providing nucleation sites for the de novo adhesion of coadhering streptococci.

Biofilm growth of Lactobacillus species is promoted by Actinomyces species and Streptococcus mutans

The ability of oral bacteria to integrate within a biofilm is pivotal to their survival. A dependence on the amount of biofilm growth by noncoaggregating Lactobacillus rhamnosus and Lactobacillus plantarum on coculture with Actinomyces naeslundii, Actinomyces gerencseriae, Streptococcus mutans and Veillonella parvula was investigated using an artificial-mouth culture system. Biofilm formation by the lactobacilli in mono-culture was poor. In coculture with Actinomyces species the amount of L. rhamnosus increased 7-20 times and L. plantarum 4-7 times compared to its mono-culture biofilm. S. mutans also promoted substantial biofilm growth of lactobacilli but V. parvula had no effect. We conclude that these Actinomyces species promoted growth of key Lactobacillus species in a biofilm, as did S. mutans to a smaller extent, and that the ability of individual bacteria to form mono-culture biofilms is not necessarily an indicator of their survival and pathogenic potential in a complex multispecies biofilm community.