Dental plaque as a microbial biofilm

Microbiota of plaque microcosm biofilms: effect of three times daily sucrose pulses in different simulated oral environments

AIM

To explore the Ecological Plaque Hypothesis for dental caries. To test modification of the microbiota of dental plaque microcosm biofilms by sucrose pulsing during growth in two different simulated oral fluids, and with a urea-induced plaque pH elevation.

METHODS

Plaque microcosm biofilms were cultured in an 'artificial mouth' with and without 6-min 5% w/v sucrose pulses every 8 h in an environment of continuously supplied saliva-like defined medium with mucin (DMM), or basal medium mucin (BMM, a high-peptone-yeast extract oral fluid analogue), and also in DMM + 10 mmol/l urea, with sucrose pulsing. Forty plaque species were quantified by checkerboard DNA:DNA hybridization analysis.

RESULTS

Sucrose pulsing extended rapid plaque growth in DMM and BMM, inducing major microbiota changes in DMM but not in BMM. In DMM, some streptococci and lactobacilli were unaffected while others implicated in caries, together with Candida albicans and Capnocytophaga gingivalis, increased. Aerobic, microaerophilic and major anaerobic species decreased. Elevation of the pH(max) from 6.4 to 7.0 had almost no effect on the microbiota. BMM plaques were distinct from DMM plaques with particularly low levels of Candida albicans and Actinomyces.

CONCLUSIONS

Modest sucrose exposure in a saliva-like environment causes profound changes in the developmental self-organization of plaque microcosms, supporting the Ecological Plaque Hypothesis. Nevertheless, there is significant stability in microbial composition with varying pH near neutrality. Increases in levels of specific bacteria in response to sucrose could be characteristic of organisms particularly important in caries.

Adhesion of Streptococcus sanguinis to Dental Implant and Restorative Materials in vitro

Bacterial adhesion to tooth surfaces or dental materials starts immediately upon exposure to the oral environment. The aim of this study, therefore, was to compare the adhesion of Streptococcus sanguinis to saliva-coated human enamel and dental materials - during a one-hour period - using an in vitro flow chamber system which mimicked the oral cavity. After fluorescent staining, the number of adhered cells and their vitality were recorded. The dental materials used were: titanium (Rematitan M), gold (Neocast 3), ceramic (Vita Omega 900), and composite (Tetric Ceram). The number of adherent bacterial cells was higher on titanium, gold, and ceramic surfaces and lower on composite as compared to enamel. As for the percentage of adherent vital cells, it was higher on enamel than on the restorative materials tested. These results suggested that variations in the number and vitality of the adherent pioneer oral bacteria, S. sanguinis, in the in vitro system depended on the surface characteristics of the substratum and the acquired salivary pellicle. The in vitro adhesion model used herein provided a simple and reproducible approach to investigate the impact of surface-modified dental materials on bacterial adhesion and vitality.

Acyl-substituted dermaseptin S4 derivatives with improved bactericidal properties, including on oral microflora

The 15-mer dermaseptin S4 derivative S4(1-15) was recently shown to exhibit potent activity against oral pathogens associated with caries and periodontitis. Here, we investigated possible modes for improving the peptide's properties through systematic replacement of an N-terminal amino acid(s) with various fatty acids that modulate the peptide's hydrophobicity and/or charge. Deletion of 1 to 3 residues led to progressive loss of potency as assessed by MIC experiments performed on four test bacteria. Replacing the deleted amino acids with fatty acids most often resulted in potency recovery or improvement, as evidenced by lower MICs and faster bactericidal kinetics in culture media. Best results were obtained after replacement of the N-terminal dipeptide alanine-leucine with heptanoic (C7) or aminododecanoic (NC12) acid. Circular dichroism analysis correlated antibacterial properties to the peptide's secondary structure. MIC experiments and confocal laser scanning microscopy results indicated that C7-S4(3-15) and NC12-S4(3-15) were bactericidal to various oral pathogens, including those which are immobilized in a biofilm. C7-S4(3-15) performed similarly to or better than (depending on growth medium) IB-367, a peptide assessed in clinical trials for treatment of oral mucositis, reducing CFU counts by >3 log units within 2 min of incubation. Collectively, the data indicate that substitution of fatty acids for amino acids may be a useful strategy in revealing improved derivatives of known antimicrobial peptides and suggest the suitability of such compounds for controlling pathogens associated with oral diseases.

Effect of material characteristics and/or surface topography on biofilm development

BACKGROUND

From an ecological viewpoint, the oral cavity, in fact the oro-pharynx, is an 'open growth system'. It undergoes an uninterrupted introduction and removal of both microorganisms and nutrients. In order to survive within the oro-pharyngeal area, bacteria need to adhere either to the soft or hard tissues in order to resist shear forces. The fast turn-over of the oral lining epithelia (shedding 3 x/day) is an efficient defence mechanism as it prevents the accumulation of large masses of microorganisms. Teeth, dentures, or endosseous implants, however, providing non-shedding surfaces, allow the formation of thick biofilms. In general, the established biofilm maintains an equilibrium with the host. An uncontrolled accumulation and/or metabolism of bacteria on the hard surfaces forms, however, the primary cause of dental caries, gingivitis, periodontitis, peri-implantitis, and stomatitis.

OBJECTIVES

This systematic review aimed to evaluate critically the impact of surface characteristics (free energy, roughness, chemistry) on the de novo biofilm formation, especially in the supragingival and to a lesser extent in the subgingival areas.

METHODS

An electronic Medline search (from 1966 until July 2005) was conducted applying the following search items: 'biofilm formation and dental/oral implants/surface characteristics', 'surface characteristics and implants', 'biofilm formation and oral', 'plaque/biofilm and roughness', 'plaque/biofilm and surface free energy', and 'plaque formation and implants'. Only clinical studies within the oro-pharyngeal area were included.

RESULTS

From a series of split-mouth studies, it could be concluded that both an increase in surface roughness above the R(a) threshold of 0.2 microm and/or of the surface-free energy facilitates biofilm formation on restorative materials. When both surface characteristics interact with each other, surface roughness was found to be predominant. The biofilm formation is also influenced by the type (chemical composition) of biomaterial or the type of coating. Direct comparisons in biofilm formation on different transmucosal implant surfaces are scars.

CONCLUSIONS

Extrapolation of data from studies on different restorative materials seems to indicate that transmucosal implant surfaces with a higher surface roughness/surface free energy facilitate biofilm formation.

Principles of Antimicrobial Therapy

The most compelling reason for practicing judicious antimicrobial use is to facilitate therapeutic success. The definition of therapeutic success has changed in recent years, however; not only does success include eradication of infection, but it must now include avoidance of resistance. If the goal of antimicrobial therapy is to achieve sufficient concentrations at the site of infection such that the infecting organism is killed, therapy should be successful.

The effect of cocoa polyphenols on the growth, metabolism, and biofilm formation by Streptococcus mutans and Streptococcus sanguinis

The aim of this study was to determine if cocoa polyphenols could interfere with biofilm formation by Streptococcus mutans or Streptococcus sanguinis, and reduce acid production from sucrose by S. mutans. The antimicrobial activity of cocoa polyphenols was assessed against cariogenic (S. mutans) and health-associated (S. sanguinis) species by minimum inhibitory concentration assays. Cocoa polyphenol dimer, tetramer, and pentamer inhibited the growth of S. sanguinis, whereas the growth of S. mutans was unaffected. However, pretreatment of surfaces with cocoa polyphenol pentamer (35 microM) reduced biofilm formation by S. mutans at 4 and 24 h, whereas the effects on S. sanguinis were less consistent. In contrast, brief exposure of preformed biofilms to pentamer either had no significant effect or resulted in increased counts of S. mutans under certain conditions. Cocoa polyphenol pentamer (500 microM) significantly reduced the terminal pH, and inhibited the rate of acid production by S. mutans at pH 7.0. In conclusion, cocoa polyphenols can reduce biofilm formation by S. mutans and S. sanguinis, and inhibit acid production by S. mutans.

Antibacterial action of photoactivated disinfection {PAD} used on endodontic bacteria in planktonic suspension and in artificial and human root canals

OBJECTIVES

To measure antibacterial action of photoactivated disinfection (PAD) on endodontic bacteria in planktonic suspension and root canals.

METHODS

Four bacteria, Fusobacterium nucleatum,Peptostreptococcus micros, Prevotella intermedia and Streptococcus intermedius, were tested in suspension. After mixing equal volumes of Tolonium chloride and bacterial suspension for 60s, each 200 microL of concentration (>10(6)cfu mL(-1)) was irradiated with light at 633+/-2 nm. Each energy dose/Tolonium chloride concentration combination was tested eight times, with controls. Prepared root canals in Training Blocs and extracted human teeth were inoculated with S. intermedius followed by 10 mg L(-1) Tolonium chloride or saline. Bacteria in canals were sampled before and after light irradiation. Student t-test assessed significance of changes in viable bacteria produced by treatment of either light or Tolonium chloride alone and light/Tolonium chloride combinations.

RESULTS

In suspension, reductions in bacteria were highly significant (P<0.01) for light/Tolonium chloride combinations compared to light or Tolonium chloride alone. Maximum mean log reductions of 1.14 (P. intermedia), 2.48 (P. micros), 2.81 (F. nucleatum) and 6.73 (S. intermedius) were at 4.8 J/20 mg L(-1). Antibacterial action was increased by energy dose increase (not always significantly), but not by Tolonium chloride concentration. In control canals mean log reductions of 0.42 (Blocs) and 0.38 (teeth) from initial levels were not significant. PAD mean log reductions of 2.40 (Blocs) and 2.01 (teeth) were highly significant. Changes for PAD/energy dose combinations were not significant.

CONCLUSION

PAD killed endodontic bacteria at statistically significant levels compared to controls. Kills varied with bacterial species.

Dental plaque as a biofilm and a microbial community - implications for health and disease

Dental plaque is a structurally- and functionally-organized biofilm. Plaque forms in an ordered way and has a diverse microbial composition that, in health, remains relatively stable over time (microbial homeostasis). The predominant species from diseased sites are different from those found in healthy sites, although the putative pathogens can often be detected in low numbers at normal sites. In dental caries, there is a shift toward community dominance by acidogenic and acid-tolerating species such as mutans streptococci and lactobacilli, although other species with relevant traits may be involved. Strategies to control caries could include inhibition of biofilm development (e.g. prevention of attachment of cariogenic bacteria, manipulation of cell signaling mechanisms, delivery of effective antimicrobials, etc.), or enhancement of the host defenses. Additionally, these more conventional approaches could be augmented by interference with the factors that enable the cariogenic bacteria to escape from the normal homeostatic mechanisms that restrict their growth in plaque and out compete the organisms associated with health. Evidence suggests that regular conditions of low pH in plaque select for mutans streptococci and lactobacilli. Therefore, the suppression of sugar catabolism and acid production by the use of metabolic inhibitors and non-fermentable artificial sweeteners in snacks, or the stimulation of saliva flow, could assist in the maintenance of homeostasis in plaque. Arguments will be presented that an appreciation of ecological principles will enable a more holistic approach to be taken in caries control.

Microbiological diagnostics in oral diseases

Most infections of the oral cavity, including the major dental diseases caries and periodontitis, are opportunistic in nature. They are caused or maintained by microorganisms of the resident or transient flora normally present in low numbers and not pathogenic, but in certain circumstances develop infections. Mucosal infections have some degree of specificity [e.g. Candida spp., Staphylococcus aureus, and enterics] and a microbiological test can be interpreted accurately for clinical diagnosis and choice of treatment. Subepithelial or deep infections, however, include a number of species from the resident flora, mainly anaerobes whose role in the infections is difficult to interpret. However, microbiological tests and the presence of certain bacterial species could be used for treatment control, risk-evaluation and even for patient motivation in the prevention of these diseases. Microbiological diagnosis can be used in general practice for several purposes and in various situations that can be of great value for the dental patient.

In vitro biofilm formation on the surface of resin-based dentine adhesives

Prevention of root caries on exposed root surfaces in the aging population is a significant challenge. Bonding resins can be applied to exposed root surfaces as sealants; however, minimal data exists regarding biofilm formation on the surface of these resins. We hypothesized that an antibacterial dentine-bonding resin containing methacryloxydodecyl-pyridiniumbromide (MDPB) may reduce biofilm formation. Biofilms were produced in pooled stimulated natural whole saliva, supplemented with 1% sucrose, on the surface of 5 dentine-bonding resins (Clearfil SE, OptiBond Solo, Protect Bond, Protect Bond Primer, and Xeno III) using untreated root surfaces as controls. Biofilms were stained using the Live:Dead Baclight bacterial viability stain, viewed with confocal microscopy, and analyzed using ImageJ image-analysis software. Resin surfaces encouraged attachment of live bacteria compared with root surfaces. All resins showed similar bacterial colonization in sections adjacent to the resin surface, but in the central and outer portions of biofilms, Xeno III and Protect Bond Primer showed a viable bacterial load similar to that of the root surface. Fluoride-releasing resins (OptiBond Solo/Protect Bond) did not show reduced biofilm formation. Thus, antibacterial agents within the resins have a minimal effect on biofilm formation, particularly when directly adjacent to the root surface.

Communication in bacteria: an ecological and evolutionary perspective

Individual bacteria can alter their behaviour through chemical interactions between organisms in microbial communities - this is generally referred to as quorum sensing. Frequently, these interactions are interpreted in terms of communication to mediate coordinated, multicellular behaviour. We show that the nature of interactions through quorum-sensing chemicals does not simply involve cooperative signals, but entails other interactions such as cues and chemical manipulations. These signals might have a role in conflicts within and between species. The nature of the chemical interaction is important to take into account when studying why and how bacteria react to the chemical substances that are produced by other bacteria.

Sustained-release delivery systems of triclosan for treatment ofStreptococcus mutans biofilm

Dental diseases are chronic infections caused by oral bacteria harboring the dental biofilm. Local sustained-release delivery systems prolong the duration of a drug in the oral cavity, thus enhancing its therapeutic potential, while reducing its side effects. Triclosan is an agent that was found to have an antibacterial effect against oral bacteria. However, its substantivity in the oral cavity is low, resulting in reduced antibacterial efficiency. The purpose of this study was to develop a local sustained release device containing triclosan and to test its antibacterial efficacy on Streptococcus mutans biofilm. Our results show that we can formulate an ethylcellulose-based, nondegradable, sustained-release device in which 80% of the loaded triclosan is released over a 10-day period. The release rate of triclosan corresponded to the Higuchi's planar homogenous diffusion release model (r2 = 0.998). A degradable local sustained-release delivery based on a methacrylate ester matrix was also developed for a faster release rate of triclosan. The release kinetics in those types of sustained-release delivery systems was erosion control. The local sustained-release delivery system significantly affected the viability of S. mutans in biofilm compared to placebo as was tested by confocal laser scanning microscopy. Our in vitro results show that triclosan can be incorporated into degradable or nondegradable sustained-release drug delivery systems. The release of triclosan from the local sustained-release delivery system can be controlled, thus extending its antibacterial properties.

Inhibitory effects of cranberry polyphenols on formation and acidogenicity ofStreptococcus mutansbiofilms

Cranberry fruit is a rich source of polyphenols, and has shown biological activities against Streptococcus mutans. In the present study, we examined the influence of extracts of flavonols (FLAV), anthocyanins (A) and proanthocyanidins (PAC) from cranberry on virulence factors involved in Streptococcus mutans biofilm development and acidogenicity. PAC and FLAV, alone or in combination, inhibited the surface-adsorbed glucosyltransferases and F-ATPases activities, and the acid production by S. mutans cells. Furthermore, biofilm development and acidogenicity were significantly affected by topical applications of PAC and FLAV (P<0.05). Anthocyanins were devoid of any significant biological effects. The flavonols are comprised of mostly quercetin glycosides, and the PAC are largely A-type oligomers of epicatechin. Our data show that proanthocyanidins and flavonols are the active constituents of cranberry against S. mutans.

Caries-Preventive Effect of Chlorhexidine Gel Applications among High-Risk Children

Evidence on the caries-preventive effect of chlorhexidine (CHX) among high-risk children is inconclusive, possibly because obscured by fluoride exposure. We investigated the effect of CHX among initially 3-year-old subjects whose baseline d(3)ft was = 0 and whose only regular fluoride exposure came from toothpaste. The subjects were assigned to three groups: high-risk test (HRT, n = 70), high-risk control (HRC, n = 71), and low-risk control (LRC, n = 70). Risk classification was based on salivary mutans streptococcal levels (MS, </>or=1.0 x 10(5) cfu/ml). Basic measures (oral hygiene, dietary counselling every 4 months) were given to all groups. HRT also underwent CHX gel applications for 3 consecutive days at 3-month intervals for 15 months. Eighteen months after baseline d(3)ft increments and proportions of children with d(3)ft increment >or=1 (%d(3)ft increment >or=1) among all groups were assessed. Anti-MS effect on high-risk children and caries-preventive effect on all children were statistically analysed by residual change analysis (MS), non-parametric tests and logistic regression analysis (caries). No differences were found between the groups in basic programme compliance. CHX significantly reduced MS levels. %d(3)ft increment >or=1 and mean d(3)ft increments were 34.3%, 0.56 (HRT), 32.4%, 0.54 (HRC) and 11.4%, 0.11 (LRC), with HRT/HRC values statistically significantly higher than LRC values and no significant difference between HRT and HRC. HRT children were not less likely to show new lesions than HRC children (OR = 1.09; 95% confidence interval 0.54-2.19), while high-risk children were 4 times more likely to show new lesions than low-risk children (OR = 3.71; 95% confidence interval 1.53-9.03). CHX gel applications showed moderate anti-MS effect but negligible caries-preventive effect.

Microscopic observation of bacteria: review highlighting the use of environmental SEM

Throughout the years, various methods have been adopted to investigate bacteria involved in root canal infection and apical periodontitis. This paper reviews the most commonly used microscopic techniques and discusses their possibilities, limitations and sample preparation. In particular, a recently developed variant of scanning electron microscope (SEM), referred to as environmental SEM (ESEM), is highlighted due to its potential impact across the diverse field of biomaterials research. The performance of this ESEM technique for bacterial observation of endodontic pathogens was illustrated by a practical approach. The paper concludes with a discussion on the possible use of ESEM for testing endodontic treatment modalities under environmental conditions in situ.

Competition and coexistence between Streptococcus mutans and Streptococcus sanguinis in the dental biofilm

The human mucosal surface is colonized by the indigenous microflora, which normally maintains an ecological balance among different species. Certain environmental or biological factors, however, may trigger disruption of this balance, leading to microbial diseases. In this study, we used two oral bacterial species, Streptococcus mutans and Streptococcus sanguinis (formerly S. sanguis), as a model to probe the possible mechanisms of competition/coexistence between different species which occupy the same ecological niche. We show that the two species engage in a multitude of antagonistic interactions temporally and spatially; occupation of a niche by one species precludes colonization by the other, while simultaneous colonization by both species results in coexistence. Environmental conditions, such as cell density, nutritional availability, and pH, play important roles in determining the outcome of these interactions. Genetic and biochemical analyses reveal that these interspecies interactions are possibly mediated through a well-regulated production of chemicals, such as bacteriocins (produced by S. mutans) and hydrogen peroxide (produced by S. sanguinis). Consistent with the phenotypic characteristics, production of bacteriocins and H2O2 are regulated by environmental conditions, as well as by juxtaposition of the two species. These sophisticated interspecies interactions could play an essential part in balancing competition/coexistence within multispecies microbial communities.

Dental plaque: biological significance of a biofilm and community life-style

BACKGROUND

Most microorganisms in nature attach to surfaces and form matrix-embedded biofilms. Biofilms are highly structured and spatially organized, and are often composed of consortia of interacting microorganisms, termed microbial communities, the properties of which are more than the sum of the component species. Microbial gene expression alters markedly in biofilms; organisms communicate by gene transfer and by secretion of diffusible signalling molecules. Cells in biofilms are less susceptible to antimicrobial agents.

AIM AND MATERIALS & METHODS

To comprehensively review the literature to determine whether dental plaque displays properties consistent with those of a typical biofilm and microbial community.

RESULTS

Novel microscopic and molecular techniques have demonstrated that plaque has a structured architecture with an extracellular matrix, and a diverse composition (around 50% of cells are unculturable). The constituent species communicate by gene transfer, by secreted peptides (gram-positive bacteria) and autoinducer-2 (gram-positive and gram-negative bacteria). These organisms are functionally organized for increased metabolic efficiency, greater resistance to stress and for enhanced virulence. Plaque formation has direct and indirect effects on gene expression.

CONCLUSION

Dental plaque displays properties that are typical of biofilms and microbial communities in general, a clinical consequence of which is a reduced susceptibility to antimicrobial agents as well as pathogenic synergism.

Oral microbial communities in sickness and in health

The relationship between humans and their oral microflora begins shortly after birth and lasts a lifetime. Up until fairly recently, the associations between the host and oral bacteria were considered in terms of a multiplicity of single species interactions. However, it is becoming more apparent that the oral microbes comprise a complex community, and that oral health or disease depends on the interface between the host and the microbial community as a whole. Although it is important to continue studies of the pathogenic properties of specific microbes, these are relevant only in the context of the properties of the community within which they reside. Understanding the microbial communities that drive sickness or health is a key to combating human oral diseases.

Variation in bacterial DGGE patterns from human saliva: over time, between individuals and in corresponding dental plaque microcosms

OBJECTIVE

Eubacterial 16S rDNA fingerprints of human saliva and dental plaque microcosm biofilms grown in the multi-plaque artificial mouth (MAM) were characterised using denaturing gradient gel electrophoresis (DGGE).

DESIGN

The stability of the bacterial community in the saliva of one individual collected over 7 years was assessed and compared with bacterial patterns in the saliva of 10 different individuals. DGGE was also used to assess changes in bacterial composition between saliva and mature plaque microcosms developed in the MAM from these 10 individual saliva samples.

RESULTS

A relatively stable bacterial community (>87% concordance) was maintained within the individual oral environment of the standard donor over 7 years of monitoring. By comparison, DGGE fingerprint patterns of saliva from 10 different donors displayed greater variability (66% concordance). Variability between individual DGGE profiles increased further in mature plaque microcosms grown from the saliva of the 10 donors (52% concordance) with an increase in detected species diversity and evidence for conserved similarity and hence the maintenance of organisation during community development.

CONCLUSIONS

These results suggest that stable ecological conditions were maintained long-term within the oral environment of the individual saliva donor but that transient fluctuations also occurred. The ecology and predominating microbiota in different individuals was host-specific and these differences were maintained to a degree during development into mature plaque microcosms. These findings also demonstrate the potential usefulness of applying DGGE to monitor temporal and developmental changes and possibly pathogenic patterns in oral bacterial communities from saliva and plaque.

Phenotypic and genotypic selection of microbiota surviving under dental restorations

The effects of sealing infected carious dentine below dental restorations on the phenotypic and genotypic diversity of the surviving microbiota was investigated. It was hypothesized that the microbiota would be subject to nutrient limitation or nutrient simplification, as it would no longer have access to dietary components or salivary secretion for growth. The available nutrients would be limited primarily to serum proteins passing from the pulp through the patent dentinal tubules to the infected dentine. Ten lesions were treated, and infected dentine was sealed below dental restorations for approximately 5 months. Duplicate standardized samples of infected dentine were taken at baseline and after the removal of the restorations. The baseline microbiota were composed primarily of Lactobacillus spp., Streptococcus mutans, Streptococcus parasanguinis, Actinomyces israelii, and Actinomyces gerencseriae. None of these taxa were isolated among the microbiota of the dentine samples taken after 5 months, which consisted of only Actinomyces naeslundii, Streptococcus oralis, Streptococcus intermedius, and Streptococcus mitis. The microbiota of the final sample exhibited a significantly (P < 0.001) increased ability to produce glycosidic enzymes (sialidase, beta-N-acetylglucosaminidase, and beta-galactosidase), which liberate sugars from glycoproteins. The genotypic diversity of S. oralis and A. naeslundii was significantly (P = 0.002 and P = 0.001, respectively) reduced in the final samples. There was significantly (P < 0.001) greater genotypic diversity within these taxa between the pairs of dentine samples taken at baseline than was found in the 5-month samples, indicating that the dentine was more homogenous than it was at baseline. We propose that during the interval between placement of the restorations and their removal, the available nutrient, primarily serum proteins, or the relative simplicity and homogeneity of the nutrient supply significantly affected the surviving microbiota. The surviving microbiota was less complex, based on compositional, phenotypic, and genotypic analyses, than that isolated from carious lesions which were also exposed to salivary secretions and pH perturbations.

Bacterial Biofilms and Ocular Infections

Serious bacterial infections of the eye are often associated with abiotic prosthetic materials, such as contact lenses, intraocular lenses, and scleral buckles. In recent years, microbiologists have recognized substantial differences between bacteria growing in a sessile community attached to a surface and free-living or planktonic bacteria. These sessile surface-attached communities are known as biofilms, whose properties have important consequences for clinical medicine. As a population, bacteria in biofilms are more resistant to antimicrobial agents and the immune system, and they are more persistent than planktonic bacteria in hostile environments. These characteristics are likely the result of both biofilm-specific phenotypes and increased phenotypic diversity within biofilms as compared with planktonic communities of bacteria. Bacterial biofilm formation has been observed on human tissues, as well as on abiotic prosthetic devices. A better understanding of biofilm formation may lead to the development of novel antimicrobial agents as well as prosthetic devices that are resistant to bacterial colonization.