The formation of mixed culture biofilms of oral species along a gradient of shear stress

Photoacoustic removal of Enterococcus faecalis biofilms from titanium surface with an Er:YAG laser using super short pulses

Biofilms that grow on implant surfaces pose a great risk and challenge for the dental implant survival. In this work, we have applied Er:YAG photoacoustic irrigation using super short pulses (Er:YAG-SSP) to remove biofilms from the titanium surfaces in the non-contact mode. Mature Enterococcus faecalis biofilms were treated with saline solution, chlorhexidine, and hydrogen peroxide, or photoacoustically with Er:YAG-SSP for 10 or 60 s. The number of total and viable bacteria as well as biofilm surface coverage was determined prior and after different treatments. Er:YAG-SSP photoacoustic treatment significantly increases the biofilm removal rate compared to saline or chemically treated biofilms. Up to 92% of biofilm-covered surface can be cleaned in non-contact mode during 10 s without the use of abrasives or chemicals. In addition, Er:YAG-SSP photoacoustic irrigation significantly decreases the number of viable bacteria that remained on the titanium surface. Within the limitations of the present in vitro model, the ER:YAG-SSP seems to constitute an efficient therapeutic option for quick debridement and decontamination of titanium implants without using abrasives or chemicals.

Discovery, development and exploitation of steady-state biofilms

Early in vitro biofilm models go back even beyond the invention of the word 'biofilm'. In the dental field, biofilms were simply known as dental plaque and many of the first in vitro models were termed 'artificial mouth microcosm plaques'. The purpose of this review is to highlight important elements of research from over the years regarding in vitro biofilm models, including data from our own laboratories. This helps us to interpret the models and point the way to the future development of biofilm testing. Many hypotheses regarding biofilm phenomena, particularly ecology, metabolism and physiology of volatile sulphur compounds (VSCs) and volatile organic compound (VOC) production could potentially be supported or disproved. In this way, the methods we use for screening biologically active agents including inhibitors, biocides and antimicrobial compounds in general can be improved. Hopefully, any lessons learnt in the past may be of value for the future. In this review, we focus around the need for growth rate controlled long-term biofilms; being continuously monitored using recent technical advances in bioluminescence, selective real-time electrodes, pH electrodes and continuous on-line analysis of the gas phase (both qualitatively and quantitatively). These features allow for accurate determination of growth rate and/or metabolic rate as well as pave the way towards automated assays and fine control of metabolism; impossible to achieve according to conventional biofilm theory. We also attempt to address the questions; can biofilm systems be improved to maintain long term 'real' or 'true' steady states over weeks or months, or are we limited to quasi-steady state systems for a limited period of time.

Live Cell Analysis of Shear Stress on Pseudomonas aeruginosa Using an Automated Higher-Throughput Microfluidic System

A higher-throughput microfluidic in vitro bioreactor coupled with fluorescence microscopy has been used to study bacterial biofilm growth and morphology, including Pseudomonas aeruginosa (P. aeruginosa). Here, we will describe how the system can be used to study the growth kinetics and the morphological properties such as the surface roughness and textural entropy of P. aeruginosa strain PA01 that expresses an enhanced green fluorescent protein (PA01-EGFP). A detailed protocol will describe how to grow and seed PA01-EGFP cultures, how to set up the microscope and autorun, and conduct the image analysis to determine growth rate and morphological properties using a variety of shear forces that are controlled by the microfluidic device. This article will provide a detailed description of a technique to improve the study of PA01-EGFP biofilms which eventually can be applied towards other strains of bacteria, fungi, or algae biofilms using the microfluidic platform.

Comparison of periodontitis-associated oral biofilm formation under dynamic and static conditions

Purpose

The purpose of this study was to compare the characteristics of single- and dual-species in vitro oral biofilms made by static and dynamic methods.

Methods

Hydroxyapatite (HA) disks, 12.7 mm in diameter and 3 mm thick, were coated with processed saliva for 4 hours. The disks were divided into a static method group and a dynamic method group. The disks treated with a static method were cultured in 12-well plates, and the disks in the dynamic method group were cultured in a Center for Disease Control and Prevention (CDC) biofilm reactor for 72 hours. In the single- and dual-species biofilms, Fusobacterium nucleatum and Porphyromonas gingivalis were used, and the amount of adhering bacteria, proportions of species, and bacterial reduction of chlorhexidine were examined. Bacterial adhesion was examined with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM).

Results

Compared with the biofilms made using the static method, the biofilms made using the dynamic method had significantly lower amounts of adhering and looser bacterial accumulation in SEM and CLSM images. The proportion of P. gingivalis was higher in the dynamic method group than in the static method group; however, the difference was not statistically significant. Furthermore, the biofilm thickness and bacterial reduction by chlorhexidine showed no significant differences between the 2 methods.

Conclusions

When used to reproduce periodontal biofilms composed of F. nucleatum and P. gingivalis, the dynamic method (CDC biofilm reactor) formed looser biofilms containing fewer bacteria than the well plate. However, this difference did not influence the thickness of the biofilms or the activity of chlorhexidine. Therefore, both methods are useful for mimicking periodontitis-associated oral biofilms.

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

An understanding of biofilm behavior of periodontopathic bacteria is key to the development of effective oral therapies. We hypothesized that interspecies bacterial aggregates play an important role in anaerobic biofilm establishment and proliferation, and contribute to the survivability of the biofilm against therapeutic agents. The system developed in this study assessed a multi-species ( Streptococcus gordonii, Actinobacillus actinomycetemcomitans, and Fusobacterium nucleatum) biofilm formation under anaerobic and flowing conditions with the use of an in situ image analysis system. The biofilm was comprised of a base film of non-aggregated cells and complex interspecies aggregates that formed in the planktonic phase which rapidly colonized the surface, reaching 58 ± 9% and 65 ± 11.8% coverage by 5 and 24 hrs, respectively. Upon SDS (0.1%) treatment of a 24-hour biofilm, substantial detachment (55 ± 14%, P < 0.05) of the aggregates was observed, while the base film bacteria remained attached but non-viable. Rapid re-establishment of the biofilm occurred via attachment of viable planktonic aggregates.

From Mouth to Model: Combining in vivo and in vitro Oral Biofilm Growth

Background: Oral biofilm studies based on simplified experimental setups are difficult to interpret. Models are limited mostly by the number of bacterial species observed and the insufficiency of artificial media. Few studies have attempted to overcome these limitations and to cultivate native oral biofilm. Aims: This study aimed to grow oral biofilm in vivo before transfer to a biofilm reactor for ex situ incubation. The in vitro survival of this oral biofilm and the changes in bacterial composition over time were observed. Methods: Six human enamel-dentin slabs embedded buccally in dental splints were used as biofilm carriers. Fitted individually to the upper jaw of 25 non-smoking male volunteers, the splints were worn continuously for 48 h. During this time, tooth-brushing and alcohol-consumption were not permitted. The biofilm was then transferred on slabs into a biofilm reactor and incubated there for 48 h while being nourished in BHI medium. Live/dead staining and confocal laser scanning microscopy were used to observe bacterial survival over four points in time: directly after removal (T0) and after 1 (T1), 24 (T2), and 48 h (T3) of incubation. Bacterial diversity at T0 and T3 was compared with 454-pyrosequencing. Fluorescence in situ hybridization (FISH) was performed to show specific taxa. Survival curves were calculated with a specially designed MATLAB script. Acacia and QIIME 1.9.1 were used to process pyrosequencing data. SPSS 21.0 and R 3.3.1 were used for statistical analysis. Results: After initial fluctuations at T1, survival curves mostly showed approximation of the bacterial numbers to the initial level at T3. Pyrosequencing analysis resulted in 117 OTUs common to all samples. The genera Streptococcus and Veillonella (both Firmicutes) dominated at T0 and T3. They make up two thirds of the biofilm. Genera with lower relative abundance had grown significantly at T3. FISH analysis confirmed the pyrosequencing results, i.e., the predominant staining of Firmicutes. Conclusion: We demonstrate the in vitro survival of native primary oral biofilm in its natural complexity over 48 h. Our results offer a baseline for cultivation studies of native oral biofilms in (phyto-) pharmacological and dental materials research. Further investigations and validation of culturing conditions could also facilitate the study of biofilm-induced diseases.

Cells in shearable and nonshearable regions of Salmonella enterica serovar Enteritidis biofilms are morphologically and physiologically distinct

Cellular morphology, exopolymer chemistry, and protein expression of shearable and nonshearable fractions of Salmonella enterica serovar Enteritidis biofilms were examined. Biofilms were grown at a laminar flow velocity of 0.07 cm.s-1 for ~120 h, resulting in biofilms with a thickness (mean +/- SD) of 43 +/- 24 microm. An empirically determined shear-inducing flow (1.33 cm.s-1) was then applied for 5 min, effectively reducing biofilm thickness by ~70% and leaving 13 +/- 6 microm of nonshearable material and allowing fractionation of biofilm material into shearable and nonshearable regions. In situ lectin binding analyses revealed that there was no significant difference in the exopolymer glycoconjugate composition of the shearable and nonshearable biofilm zones. Length to width indices of cells from nonshearable and shearable biofilm regions as well as planktonic cells from biofilm effluent and continuous culture were determined to be 3.2, 2.3, 2.2, and 1.7, respectively, indicating that the cells in the shearable fraction were morphologically more similar to planktonic cells than the cells in the nonshearable biofilm fraction. Enhanced expression of proteins involved in cold shock response, adaptation, and broad regulatory functions (CspA, GrcA, and Hns, respectively) in cells from the shearable region as well as protein translation and modification and enhanced expression of protein involved in heat shock response and chaperonin function (DnaK) in cells from the nonshearable region revealed that the physiological status of cells in the two biofilm regions was distinct. This was also reflected in the different morphologies of cells from the two biofilm zones. Stratified patterns of cell metabolism and morphology in biofilms, obtained using shear-induced biofilm fractionation, may yield important information of how cells of deeply embedded biofilm bacteria survive imposed conditions of stress such as treatment with antimicrobial agents or antibiotics.

Efficacy of removal of sucrose-supplemented interproximal plaque by electric toothbrushes in an in vitro model

Electric toothbrushes were evaluated using a model of plaque removal by fluid shear forces. Sucrose supplementation during plaque development did not affect the removal of bacteria from biofilm exposed to low-energy shear but did increase their resistance to high-energy shear. The toothbrush supplying high-energy shear forces removed significantly more viable bacteria.

Biofilm formation by Neisseria meningitidis

Biofilm formation by the human pathogen Neisseria meningitidis was analyzed. Biofilm-forming meningococcal strains were identified and quantitated by crystal violet staining. Laser scanning confocal microscopy of the meningococcal biofilm revealed variable layers up to 90 microm in thickness. A total of 39 meningococcal isolates were studied; 23 were nasopharyngeal-carriage isolates, and 16 were invasive-disease isolates. Thirty percent of carriage isolates and 12.5% of invasive-disease isolates formed biofilms proficiently on a polystyrene surface. Generally, the strains that formed biofilms showed high-level cell surface hydrophobicity, characteristic of strains lacking a capsule. The inhibitory role of capsule in biofilm formation was further confirmed by comparing the biofilm-forming capabilities of a serogroup B wild-type strain of a disease-associated isolate to those of its capsule-deficient mutant (ctrA). Some strains of meningococci form biofilms, and this process is likely important in menigococcal colonization.

Efficacy of antibiotics to strains of periodontopathogenic bacteria within a single species biofilm - an in vitro study

OBJECTIVES

This study examined differences in the efficacy of antibiotics against a single strain of three periodontal pathogens grown in an artificial biofilm.

METHODS

Single species biofilms were established with artificial saliva and one of the following bacterial strains: Actinobacillus actinomycetemcomitans Y4, Streptococcus constellatus 384b (a clinical isolate) and Porphyromonas gingivalis ATCC 33277. The efficacy of the antibiotics clindamycin, doxycycline, metronidazole, and moxifloxacin to these bacteria was determined using concentrations up to 100-fold minimal inhibitory concentration (MIC) to planctonic bacteria over 48 h.

RESULTS

The ability of the bacteria to form a biofilm varied. The biofilms of S. constellatus 384b and A. actinomycetemcomitans Y4 contained more viable bacteria and showed a larger thickness in SEM photographs than those of P. gingivalis ATCC 33277. The antibiotics tested showed different efficacy for the different strains. Moxifloxacin was the most efficient antibiotic: onefold MIC was sufficient to eliminate A. actinomycetemcomitans Y4 and P. gingivalis ATCC 33277 after 48 h. However, only the 50-fold MIC completely eradicated S. constellatus 384b. SEM photographs underlined the damaging effect of moxifloxacin on the biofilm structure.

CONCLUSION

The complete removal of bacteria by the use of antibiotics alone seems to be impossible when taking into account MIC values and the level of antibiotics in gingival fluid.