Quantifying implant-associated biofilms: Comparison of microscopic, microbiologic and biochemical methods

Gradual Acidification at the Oral Biofilm-Implant Material Interface

The colonization of dental implants by oral biofilms causes inflammatory reactions that can ultimately lead to implant loss. Therefore, safety-integrated implant surfaces are under development that aim to detect bacterial attachment at an early stage and subsequently release antibacterial compounds to prevent their accumulation. Since primary oral colonizers ferment carbohydrates leading to local acidification, pH is considered a promising trigger for these surfaces. As a prerequisite for such systems, the present study aimed at specifically analyzing the pH at the interface between implant material and oral biofilms. For this purpose, in vitro-grown Streptococcus oralis monospecies biofilms and an established multispecies biofilm on titanium discs as well as in situ-grown biofilms from orally exposed titanium-equipped splints were used. Mature biofilm morphology was characterized by live/dead fluorescence staining, revealing improved growth from in vitro to in situ biofilms as well as a general decreasing membrane permeability over time due to the static incubation conditions. For pH analysis, the pH-sensitive dye C-SNARF-4 combined with 3-dimensional imaging by confocal laser-scanning microscopy and digital image analysis were used to detect extracellular pH values in different biofilm layers. All mature biofilms showed a pH gradient, with the lowest values at the material interface. Interestingly, the exact values depicted a time- and nutrient-dependent gradual acidification independently of the biofilm source and for in situ biofilms also independently of the sample donor. After short incubation times, a mild acidification to approximately pH 6.3 could be observed. But when sufficient nutrients were processed for a longer period of time, acidification intensified, leading to approximately pH 5.0. This not only defines the required turning point of pH-triggered implant release systems but also reveals the opportunity for a tailored release at different stages of biofilm formation.

Structure and composition of early biofilms formed on dental implants are complex, diverse, subject-specific and dynamic

Biofilm-associated peri-implant infections pose a major problem in modern medicine. The understanding of biofilm development is hampered by biofilm complexity and the lack of robust clinical models. This study comprehensively characterized the dynamics of early biofilm formation in the transmucosal passage of implant abutments in 12 patients. Biofilm structures and compositions were complex, diverse, subject-specific and dynamic. A total of 371 different bacterial species were detected. 100 phylogenetically diverse unnamed species and 35 taxonomically diverse disease-associated species comprised an average 4.3% and 3.1% of the community, respectively, but reached up to 12.7% and 21.7% in some samples. Oral taxa formed numerous positive associations and clusters and were characterized by a high potential for metabolic interactions. The subspecies diversity was highly patient-specific and species-dependent, with 1427 ASVs identified in total. The unprecedented depth of early biofilm characterization in this study will support the development of individualized preventive and early diagnostic strategies.

Development and Characterization of Ammonia Removal Moving Bed Biofilms for Landfill Leachate Treatment

Urbanization growth has intensified the challenge of managing and treating increasing amounts of municipal solid waste (MSW). Landfills are commonly utilized for MSW disposal because of their low construction and operation costs. However, this practice produces huge volumes of landfill leachate, a highly polluting liquid rich in ammoniacal nitrogen (NH3-N), organic compounds, and various heavy metals, making it difficult to treat in conventional municipal wastewater treatment plants (WWTPs). In recent years, research has shown that microbial biofilms, developed on carriers of different materials and called "moving bed biofilm reactors" (MBBRs), may offer promising solutions for bioremediation. This study explored the biofilm development and the nitrification process of moving bed biofilms (MBBs) obtained from high ammonia-selected microbial communities. Using crystal violet staining and confocal laser-scanning microscopy, we followed the biofilm formation stages correlating nitrogen removal to metagenomic analyses. Our results indicate that MBBs unveiled a 10-fold more enhanced nitrification rate than the dispersed microbial community present in the native sludge of the Porto Sant'Elpidio (Italy) WWTP. Four bacterial families, Chitinophagaceae, Comamonadaceae, Sphingomonadaceae, and Nitrosomonadaceae, accumulate in structured biofilms and significantly contribute to the high ammonium removal rate of 80% in 24 h as estimated in leachate-containing wastewaters.

A photo-modulated nitric oxide delivering hydrogel for the accelerated healing of biofilm infected chronic wounds

Biofilm infection and impaired healing of chronic wounds are posing tremendous challenges in clinical practice. In this study, we presented a versatile antimicrobial hydrogel capable of delivering nitric oxide (NO) in a controllable manner to dissipate biofilms, eliminate microorganisms, and promote the healing of chronic wounds. This hydrogel was constructed by Schiff-base crosslinking of oxidized dextran and antimicrobial peptide ε-poly-lysine, further encapsulating photothermal nanoparticles bearing NO donor. This hydrogel could continuously and slowly release NO, effectively dissipating biofilms, and promoting the proliferation of mouse fibroblasts and the migration of endothelial cells. Upon exposure to NIR laser irradiation, the hydrogel generated hyperthermia and rapidly released NO, resulting in the efficient elimination of a broad spectrum of drug-resistant Gram-positive/negative bacterial and fungal biofilms through the synergistic effects of NO, photothermal therapy, and the antibacterial peptide. Notably, the hydrogel demonstrated exceptional in vivo therapeutic outcomes in accelerating the healing process of mice diabetic wounds infected with methicillin-resistant Staphylococcus aureus by successfully eliminating biofilm infection, regulating inflammation, and facilitating angiogenesis and collagen deposition. Overall, this proposed hydrogel shows great promise in accommodating the various demands of the complex repair process of chronic wounds infected with biofilms. STATEMENT OF SIGNIFICANCE: The presence of biofilm infections and underlying dysfunctions in the healing process made chronic wound become stuck in the inflammation stage and difficult to heal. This work developed a NIR laser-modulated three-stage NO-releasing versatile antimicrobial hydrogel (DEPN) exhibiting good therapeutic efficacy for chronic wound. This DEPN hydrogel could inherently and slowly released NO to disperse biofilm. Upon NIR laser irradiation, the DEPN hydrogel generated hyperthermia and induced a rapid burst release of NO effectively eliminating a broad spectrum of drug-resistant bacterial and fungal biofilms. Subsequently, the DEPN hydrogel continually release NO slowly to promote the tissue remolding. This DEPN hydrogel displays great potential in treatment of chronic wounds infected with biofilm.

Three-Dimensional Planimetry Assessment of Dental Plaque-Covered Area Reduction after Rinsing with 0.2% Sodium Hypochlorite Solution as Part of a Guided Biofilm Therapy® Protocol-Pilot Longitudinal Study

Background/Objectives: Less often employed as a rinsing solution for controlling oral biofilms, NaOCL was used in oral rinses at various concentrations in steps 1 and 4 of periodontal therapy. The aim of this study was to quantitatively evaluate the biofilm-disruptive properties of a 0.2% NaOCl solution in standardized oral rinses using dedicated plaque-disclosing agents and 3D scanning methods in patients undergoing the regular Guided Biofilm Therapy® protocol. Methods: Eight patients with at least 20 teeth present evenly distributed between the two arches were included. After 24 h of refraining from oral hygiene, dental arches were stained with a disclosing agent, the subjects rinsed for 20 s, clinical photographs and 3D scans were performed, subjects rinsed again for 20 s, photographs and 3D scans were performed again, and then the GBT® protocol was resumed as usual. Data representing areas covered with dental plaque were acquired using the "Medit Scan for Clinics" software and then underwent a post-processing and rendering process. The outcome variable was the percent reduction in the plaque-covered areas. Results: For the upper jaw, the estimated mean percent reduction in the biofilm-covered area was 39.65%, while for the mandible, it was 38.26%. The analysis of individual photographs revealed changes in the plaque-covered areas and reductions in the color intensity of the residual plaque-covered areas under identical lighting conditions. Conclusions: When analyzed using 3D intraoral scanning, the 0.2% NaOCl rinsing solution seems to be a clinically efficient disruptor/dissolvent of the oral biofilm, both when integrated into modern protocols of periodontal therapy like GBT® and for home self-care.

Biofilm volume and acidification within initial biofilms formed in situ on buccally and palatally exposed bracket material

PURPOSE

Acidification by bacterial biofilms at the bracket/tooth interface is one of the most common problems in fixed orthodontic treatments, which can lead to white spot lesions (WSL) and caries. As lingual brackets were shown to exhibit reduced WSL formation clinically, the aim of this in situ study was to compare initial intraoral biofilm formation and acidification on bracket-like specimens placed buccally and palatally in the upper jaw as a possible cause for this observation.

METHODS

Intraoral biofilm was collected from splints equipped with buccally and palatally exposed test specimens, which were worn by 12 volunteers for a total of 48 h. The test specimens consisted of standard bracket material cylinders on top of a hydroxyapatite disc to represent the bracket/tooth interface. They were analyzed for three-dimensional biofilm volume and live/dead distribution by fluorescence staining and confocal laser scanning microscopy as well as for acidification by fluorescence-based pH ratiometry.

RESULTS

Similar general biofilm morphology with regard to volume and viability could be detected for buccally and palatally exposed specimens. For pH values, biofilms from both positions showed increased acidification at the bottom layer. Interestingly, the pH value at the top layers of the biofilms was slightly lower on palatally than on buccally exposed specimens, which may likely be due to anatomic conditions.

CONCLUSION

Based on the results of this study, initial intraoral biofilm formation and acidification is almost similar on the bracket material/biomimetic tooth interface when placed buccally or palatally in the upper jaw. As lingual brackets were shown to exhibit reduced WSL formation clinically, future studies should investigate further factors like bracket geometry.

Anti-biofilm properties of laser-synthesized, ultrapure silver-gold-alloy nanoparticles against Staphylococcus aureus

Staphylococcus aureus biofilm-associated infections are a common complication in modern medicine. Due to inherent resilience of biofilms to antibiotics and the rising number of antibiotic-resistant bacterial strains, new treatment options are required. For this purpose, ultrapure, spherical silver-gold-alloy nanoparticles with homogenous elemental distribution were synthesized by laser ablation in liquids and analyzed for their antibacterial activity on different stages of S. aureus biofilm formation as well as for different viability parameters. First, the effect of nanoparticles against planktonic bacteria was tested with metabolic activity measurements. Next, nanoparticles were incubated with differently matured S. aureus biofilms, which were then analyzed by metabolic activity measurements and three dimensional live/dead fluorescent staining to determine biofilm volume and membrane integrity. It could be shown that AgAu NPs exhibit antibacterial properties against planktonic bacteria but also against early-stage and even mature biofilms, with a complete diffusion through the biofilm matrix. Furthermore, AgAu NPs primarily targeted metabolic activity, to a smaller extend membrane integrity, but not the biofilm volume. Additional molecular analyses using qRT-PCR confirmed the influence on different metabolic pathways, like glycolysis, stress response and biofilm formation. As this shows clear similarities to the mechanism of pure silver ions, the results strengthen silver ions to be the major antibacterial agent of the synthesized nanoparticles. In summary, the results of this study provide initial evidence of promising anti-biofilm characteristics of silver-gold-alloy nanoparticles and support the importance of further translation-oriented analyses in the future.

Antibacterial properties and abrasion-stability: Development of a novel silver-compound material for orthodontic bracket application

PURPOSE

Bacteria-induced white spot lesions are a common side effect of modern orthodontic treatment. Therefore, there is a need for novel orthodontic bracket materials with antibacterial properties that also resist long-term abrasion. The aim of this study was to investigate the abrasion-stable antibacterial properties of a newly developed, thoroughly silver-infiltrated material for orthodontic bracket application in an in situ experiment.

METHODS

To generate the novel material, silver was vacuum-infiltrated into a sintered porous tungsten matrix. A tooth brushing simulation machine was used to perform abrasion equal to 2 years of tooth brushing. The material was characterized by energy dispersive X‑ray (EDX) analysis and roughness measurement. To test for antibacterial properties in situ, individual occlusal splints equipped with specimens were worn intraorally by 12 periodontal healthy patients for 48 h. After fluorescence staining, the quantitative biofilm volume and live/dead distribution of the initial biofilm formation were analyzed by confocal laser scanning microscopy (CLSM).

RESULTS

Silver was infiltrated homogeneously throughout the tungsten matrix. Toothbrush abrasion only slightly reduced the material's thickness similar to conventional stainless steel bracket material and did not alter surface roughness. The new silver-modified material showed significantly reduced biofilm accumulation in situ. The effect was maintained even after abrasion.

CONCLUSION

A promising, novel silver-infiltrated abrasion-stable material for use as orthodontic brackets, which also exhibit strong antibacterial properties on in situ grown oral biofilms, was developed. The strong antibacterial properties were maintained even after surface abrasion simulated with long-term toothbrushing.

Significant removal of bacterial biofilm induced by multiple-Short ranges of electric interventions

BACKGROUND

Biofilm-related infections are serious problems in the Orthopedics field, and Staphylococcus aureus are the most popular causative agents of bacterial infections associated with arthroplasty. Several studies demonstrated a synergistic effect of the electric intervention (EI) and the antibiotic administration in killing bacteria in biofilm; however, a constant, long-time EI was needed. In the present study, the effective removal of biofilm formed with S. aureus on a titanium ring by multiple times of one minute-EI was observed and described.

METHODS

A methicillin-sensitive S. aureus clinical isolate was used to form biofilm on a titanium ring. After applying a series of EI with various combinations of the frequencies and timings, the amount and principal components of biofilms were assessed with crystal violet staining, live bacterial cell count, and fluorescence staining with confocal laser scanning microscopy.

RESULTS

More than 60% biofilm removal was observed in the 2-time EI applied at 24 (1) and 72 (3) h (days) post bacterial exposure (PBE) and in the 3-time EI at 0 (0), 24 (1), and 72 (3) h (days) PBE, or at 24 (1), 48 (2), and 72 (3) h (days) PBE. The live bacterial cell numbers, the proportion of live and dead cells, and the amount of extracellular polysaccharide substances (EPS) of biofilm were similar with or without EI. It was assumed that an excess amount of the biofilm removal shown in the several EI was not attributed to the effect of the electrolysis.

CONCLUSIONS

The effective removal of biofilm was observed when multiple times 1 min EI was applied without any changes in the proportion of live and dead bacteria or the amount of EPS. The mechanisms to explain extra biofilm removal remain to be elucidated.

Surface charge adaptive nitric oxide nanogenerator for enhanced photothermal eradication of drug-resistant biofilm infections

Due to protection of extracellular polymeric substances, the therapeutic efficiency of conventional antimicrobial agents is often impeded by their poor infiltration and accumulation in biofilm. Herein, one type of surface charge adaptable nitric oxide (NO) nanogenerator was developed for biofilm permeation, retention and eradication. This nanogenerator (PDG@Au-NO/PBAM) is composed of a core-shell structure: thermo-sensitive NO donor conjugated AuNPs on cationic poly(dopamine-co-glucosamine) nanoparticle (PDG@Au-NO) served as core, and anionic phenylboronic acid-acryloylmorpholine (PBAM) copolymer was employed as a shell. The NO nanogenerator featured long circulation and good biocompatibility. Once the nanogenerator reached acidic biofilm, its surface charge would be switched to positive after shell dissociation and cationic core exposure, which was conducive for the nanogenerator to infiltrate and accumulate in the depth of biofilm. In addition, the nanogenerator could sustainably generate NO to disturb the integrity of biofilm at physiological temperature, then generate hyperthermia and explosive NO release upon NIR irradiation to efficiently eradicate drug-resistant bacteria biofilm. Such rational design offers a promising approach for developing nanosystems against biofilm-associated infections.

Gentamicin Eluting 3D-Printed Implants for Preventing Post-Surgical Infections in Bone Fractures

A surgically implantable device is an inevitable treatment option for millions of people worldwide suffering from diseases arising from orthopedic injuries. A global paradigm shift is currently underway to tailor and personalize replacement or reconstructive joints. Additive manufacturing (AM) has provided dynamic outflow to the customized fabrication of orthopedic implants by enabling need-based design and surface modification possibilities. Surgical grade 316L Stainless Steel (316L SS) is promising with its cost, strength, composition, and corrosion resistance to fabricate 3D implants. This work investigates the possibilities of application of the laser powder bed fusion (L-PBF) technique to fabricate 3D-printed (3DP) implants, which are functionalized with a multilayered antimicrobial coating to treat potential complications arising due to postsurgical infections (PSIs). Postsurgical implant-associated infection is a primary reason for implantation failure and is complicated mainly by bacterial colonization and biofilm formation at the installation site. PLGA (poly-d,l-lactide-co-glycolide), a biodegradable polymer, was utilized to impart multiple layers of coating using the airbrush spray technique on 3DP implant surfaces loaded with gentamicin (GEN). Various PLGA-based polymers were tested to optimize the ideal lactic acid: glycolic acid ratio and molecular weight suited for our investigation. 3D-Printed PLGA-GEN substrates sustained the release of gentamicin from the surface for approximately 6 weeks. The 3DP surface modification with PLGA-GEN facilitated cell adhesion and proliferation compared to control surfaces. The cell viability studies showed that the implants were safe for application. The 3DP PLGA-GEN substrates showed good concentration-dependent antibacterial efficacy against the common PSI pathogen Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis). The GEN-loaded substrates demonstrated antimicrobial longevity and showed significant biofilm growth inhibition compared to control. The substrates offered great versatility regarding the in vitro release rates, antimicrobial properties, and biocompatibility studies. These results radiate great potential in future human and veterinary clinical applications pertinent to complications arising from PSIs, focusing on personalized sustained antibiotic delivery.

Microfluidics for Biofilm Studies

Biofilms are multicellular communities held together by a self-produced extracellular matrix and exhibit a set of properties that distinguish them from free-living bacteria. Biofilms are exposed to a variety of mechanical and chemical cues resulting from fluid motion and mass transport. Microfluidics provides the precise control of hydrodynamic and physicochemical microenvironments to study biofilms in general. In this review, we summarize the recent progress made in microfluidics-based biofilm research, including understanding the mechanism of bacterial adhesion and biofilm development, assessment of antifouling and antimicrobial properties, development of advanced in vitro infection models, and advancement in methods to characterize biofilms. Finally, we provide a perspective on the future direction of microfluidics-assisted biofilm research.

Detection of microscopic filamentous fungal biofilms - Choosing the suitable methodology

Microscopic filamentous fungi are ubiquitous microorganisms that adapt very easily to a variety of environmental conditions. Due to this adaptability, they can colonize a number of various surfaces where they are able to start forming biofilms. Life in the form of biofilms provides them with many benefits (increased resistance to desiccation, UV radiation, antimicrobial compounds, and host immune response). The aim of this study is to find a reliable and reproducible methodology to determine biofilm growth of selected microscopic filamentous fungi strains. Several methods (crystal violet staining, MTT assay, XTT assay, resazurin assay) for the determination of total biofilm biomass and its metabolic activity were tested on four fungi - Alternaria alternata, Aspergillus niger, Fusarium culmorum and Fusarium graminearum, and their biofilm was also imaged by spinning disc confocal microscopy using fluorescent dyes. A reproducible biofilm quantification method is essential for the subsequent testing of the biofilm growth suppression using antifungal agents or physical methods. Crystal violet staining was found to be a suitable method for the determination of total biofilm biomass of selected strains, and the MTT assay for the determination of metabolic activity of the biofilms. Calcofluor white and Nile red fluorescent stains successfully dyed the hyphae of microscopic fungi.

Inhibition of tooth demineralization caused by Streptococcus mutans biofilm via antimicrobial treatment using hydrogen peroxide photolysis

OBJECTIVES

An antimicrobial technique utilizing hydroxyl radicals generated by the photolysis of 3% H₂O₂ has been developed recently. The present study aimed to evaluate the effect of H₂O₂ photolysis treatment on tooth demineralization caused by Streptococcus mutans biofilm.

MATERIALS AND METHODS

To induce tooth demineralization, S. mutans biofilm was allowed to form on the maxillary first molars collected from Wistar rats via 24-h culturing. The samples were immersed in 3% H₂O₂ and irradiated with 365-nm LED (H₂O₂ photolysis treatment). Viable bacterial counts in the biofilm were evaluated immediately after treatment and after an additional 30-h culturing by colony counting. The acidogenicity of the biofilm, re-established 30 h after treatment, was assessed by measuring the pH. The effect of H₂O₂ photolysis treatment on tooth demineralization was assessed by measuring the depth of the radiolucent layer in micro-CT images.

RESULTS

H₂O₂ photolysis significantly reduced viable bacterial counts in the biofilm to 3.7 log colony forming units (CFU)/sample, while the untreated group had 7.9 log CFU/sample. The pH of the biofilm re-established after treatment (6.6) was higher than that of the untreated group (5.3). In line with the pH measurement, the treatment group had a significantly lower depth of radiolucent layer in dentin than the untreated group.

CONCLUSIONS

H₂O₂ photolysis treatment was effective not only in killing the biofilm-forming S. mutans but also in lowering the acidogenicity of the biofilm. Thus, this technique could inhibit tooth demineralization.

CLINICAL RELEVANCE

H₂O₂ photolysis can be applicable as a new dental caries treatment.

Trabecular Titanium for Orthopedic Applications: Balancing Antimicrobial with Osteoconductive Properties by Varying Silver Contents

Periprosthetic joint infection (PJI) and implant loosening are the most common complications after joint replacement surgery. Due to their increased surface area, additively manufactured porous metallic implants provide optimal osseointegration but they are also highly susceptible to bacterial colonization. Antibacterial surface coatings of porous metals that do not inhibit osseointegration are therefore highly desirable. The potential of silver coatings on arthroplasty implants to inhibit PJI has been demonstrated, but the optimal silver content and release kinetics have not yet been defined. A tight control over the silver deposition coatings can help overcome bacterial infections while reducing cytotoxicity to human cells. In this regard, porous titanium sputtered with silver and titanium nitride with increasing silver contents enabled controlling the antibacterial effect against common PJI pathogens while maintaining the metabolic activity of human primary cells. Electron beam melting additively manufactured titanium alloys, coated with increasing silver contents, were physico-chemically characterized and investigated for effects against common PJI pathogens. Silver contents from 7 at % to 18 at % of silver were effective in reducing bacterial growth and biofilm formation. Staphylococcus epidermidis was more susceptible to silver ions than Staphylococcus aureus. Importantly, all silver-coated titanium scaffolds supported primary human osteoblasts proliferation, differentiation, and mineralization up to 28 days. A slight reduction of cell metabolic activity was observed at earlier time points, but no detrimental effects were found at the end of the culture period. Silver release from the silver-coated scaffolds also had no measurable effects on primary osteoblast gene expression since similar expression of genes related to osteogenesis was observed regardless the presence of silver. The investigated silver-coated porous titanium scaffolds may thus enhance osseointegration while reducing the risk of biofilm formation by the most common clinically encountered pathogens.

What is the best technic to dislodge Staphylococcus epidermidis biofilm on medical implants?

Background

Bacterial biofilm can occur on all medical implanted devices and lead to infection and/or dysfunction of the device.

In this study, artificial biofilm was formed on four different medical implants (silicone, piccline, peripheral venous catheter and endotracheal tube) of interest for our daily clinical and/or research practice. We investigated the best conventional technic to dislodge the biofilm on the implants and quantified the number of bacteria. Staphylococcus epidermidis previously isolated from a breast implant capsular contracture on a patient in the university hospital of Dijon was selected for its ability to produce biofilm on the implants. Different technics (sonication, Digest-EUR®, mechanized bead mill, combination of sonication plus Digest-EUR®) were tested and compared to detach the biofilm before quantifying viable bacteria by colony counting.

Results

For all treatments, the optical and scanning electron microscope images showed substantial less biofilm biomass remaining on the silicone implant compared to non-treated implant.

This study demonstrated that the US procedure was statistically superior to the other physical treatment: beads, Digest-EUR® alone and Digest-EUR® + US (p < 0.001) for the flexible materials (picc-line, PIV, and silicone). The number of bacteria released by the US is significantly higher with a difference of 1 log on each material. The result for a rigid endotracheal tube were different with superiority for the chemical treatment dithiothreitol: Digest-EUR®. Surprisingly the combination of the US plus Digest-EUR® treatment was consistently inferior for the four materials.

Conclusions

Depending on the materials used, the biofilm dislodging technique must be adapted. The US procedure was the best technic to dislodge S. epidermidis biofilm on silicone, piccline, peripheral venous catheter but not endotracheal tube. This suggested that scientists should compare themselves different methods before designing a protocol of biofilm study on a given material.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02606-x.

Strategies to Improve the Potency of Oxazolidinones towards Bacterial Biofilms

Biofilms are part of the natural lifecycle of bacteria and are known to cause chronic infections that are difficult to treat. Most antibiotics are developed and tested against bacteria in the planktonic state and are ineffective against bacterial biofilms. The oxazolidinones, including the last resort drug linezolid, are one of the main classes of synthetic antibiotics progressed to clinical use in the last 50 years. They have a unique mechanism of action and only develop low levels of resistance in the clinical setting. With the aim of providing insight into strategies to design more potent antibiotic compounds with activity against bacterial biofilms, we review the biofilm activity of clinically approved oxazolidinones and report on structural modifications to oxazolidinones and their delivery systems which lead to enhanced anti-biofilm activity.

Asian Sand Dust Particles Enhance the Development of Aspergillus fumigatus Biofilm on Nasal Epithelial Cells

Background: Asian sand dust (ASD) and Aspergillus fumigatus are known risk factors for airway mucosal inflammatory diseases. Bacterial and fungal biofilms commonly coexist in chronic rhinosinusitis and fungus balls. We evaluated the effects of ASD on the development of A. fumigatus biofilm formation on nasal epithelial cells. Methods: Primary nasal epithelial cells were cultured with A. fumigatus conidia with or without ASD for 72 h. The production of interleukin (IL)-6, IL-8, and transforming growth factor (TGF)-β1 from nasal epithelial cells was determined by the enzyme-linked immunosorbent assay. The effects of ASD on A. fumigatus biofilm formation were determined using crystal violet, concanavalin A, safranin staining, and confocal scanning laser microscopy. Results: ASD and A. fumigatus significantly enhanced the production of IL-6 and IL-8 from nasal epithelial cells. By coculturing A. fumigatus with ASD, the dry weight and safranin staining of the fungal biofilms significantly increased in a time-dependent manner. However, the increased level of crystal violet and concanavalin A stain decreased after 72 h of incubation. Conclusions: ASD and A. fumigatus induced the production of inflammatory chemical mediators from nasal epithelial cells. The exposure of A. fumigatus to ASD enhanced the formation of biofilms. The coexistence of ASD and A. fumigatus may increase the development of fungal biofilms and fungal inflammatory diseases in the sinonasal mucosa.

A diguanylate cyclase regulates biofilm formation in Rhodococcus sp. NJ-530 from Antarctica

Biofilms represent a protective survival mode in which bacteria adapt themselves to the natural environment for survival purposes. Biofilm formation is regulated by 3,5-cyclic diguanylic acid (c-di-GMP), which is a universal second messenger molecule in bacteria. Diguanylate cyclase (DGC) catalyses c-di-GMP intracellular synthesis, which plays important roles in bacterial adaptation to the natural environment. In this study, the DGC gene was first cloned from Antarctic Rhodococcus sp. NJ-530. DGC contained 948 nucleotides and encoded 315 amino acids with a molecular weight of 34.6 KDa and an isoelectric point of 5.58. qRT-PCR demonstrated that the DGC expression level was significantly affected by lower salinity and temperature. Consistently, more biofilm formation occurred under the same stress. It has been shown that Rhodococcus sp. NJ-530 can adapt to the extreme environment in Antarctica, which is closely related to biofilm formation. These results provide an important reference for studying the adaptive mechanism of Antarctic microorganisms to this extreme environment.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03093-z.

Simultaneous process optimization of ultrasound-assisted extraction of polyphenols and ellagic acid from pomegranate (Punica granatum L.) flowers and its biological activities

This study was designed to optimize the extraction rate of total polyphenols and ellagic acid from pomegranate flowers. Single factors were investigated for liquid-to-material ratio (5-25), ethanol concentration (20%-60%), sonication time (5-60 min), and sonication power (150-500 W). The level range of the Box-Bokhen design was determined with respect to the single-factor results. The components of each index were normalized using the entropy weighting method for obtaining the comprehensive evaluation value. Under the actual conditions, the final optimization results were 17 for liquid-to-material ratio, 43% for ethanol concentration, 10 min for ultrasonic time, and 300 W for ultrasonic power. The extracts obtained under optimal conditions were tested for the inhibition of Streptococcus mutans and its biofilm, and results showed that pomegranate flowers exerted some inhibitory effects on the bacterium. Phosphomolybdenum and FRAP assays were used, and DPPH, ABTS, and O^2- radical scavenging tests were conducted, indicating that pomegranate flower extracts have good antioxidant capacity.

In vitro evaluation of the antibacterial effect of colloidal bismuth subcitrate on Porphyromonas gingivalis and its biofilm

OBJECTIVE

To investigate the antibacterial and anti-biofilm effects of colloidal bismuth subcitrate (CBS) on Porphyromonas gingivalis (P. gingivalis) in its planktonic and biofilm forms and also compare it with that of 0.2% chlorhexidine (CHX).

DESIGN

The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of CBS were determined by the microdilution method; the bacteriostatic rate of CBS was determined by the MTT assay; the effect of CBS on the membrane integrity of P. gingivalis was investigated by the flow cytometric methods. The effects of CBS on the biomass and bacterial activity of biofilm were investigated. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) were used to investigate the activity and structure of biofilms.

RESULTS

The MIC and MBC values were 18.75 µg/mL and 37.5 µg/mL. CBS could damage the cell membrane of P. gingivalis. CBS effectively inhibited biofilm formation and promoted dissociation at higher concentrations of 37.5 µg/mL and 75 µg/mL, respectively. The results also indicated an altered biofilm structure and reduced biofilm thickness and bacterial aggregation.

CONCLUSIONS

CBS affected the metabolic and physiological processes of P. gingivalis, inhibited the formation of biofilm, and disrupted the mature biofilm.

High-throughput screening alternative to crystal violet biofilm assay combining fluorescence quantification and imaging

The crystal violet assay is widely used for biofilm quantitation despite its toxicity and variability. Here, we instead combine fluorescence labelling with the Cytation 5 multi-mode plate reader, to enable simultaneous acquisition of both quantitative and imaging biofilm data. This high-throughput method produces more robust data and provides information about morphology and spatial species organization within the biofilm.

Characterization of Collagen/Beta Glucan Hydrogels Crosslinked with Tannic Acid

Hydrogels based on collagen/β-glucan crosslinked with tannic acid were obtained by neutralization using dialysis. The presence of tannic acid allowed obtaining stable hydrogel materials with better mechanical properties. Tannic acid was released from matrices gradually and not rapidly. The antioxidant properties of the obtained hydrogels increased over the course of their incubation in culture media and were dependent on the concentration of tannic acid in the matrices. The obtained materials influenced dehydrogenase activity and the ATP level of pathogens. Additionally, the materials' extracts improved the HaCaT cells' viability. Therefore, the obtained hydrogels seem to be promising biocompatible materials which display antimicrobial properties.

Direct anti-biofilm effects of macrolides on Acinetobacter baumannii: comprehensive and comparative demonstration by a simple assay using microtiter plate combined with peg-lid

Recently, opportunistic nosocomial infections caused by Acinetobacter baumannii have become increasingly prevalent worldwide. The pathogen often establishes biofilms that adhere to medical devices, causing chronic infections refractory to antimicrobial therapy. Clinical reports have indicated that some macrolide antibiotics are effective against chronic biofilm-related infections. In this study, we examined the direct anti-biofilm effects of seven macrolides (azithromycin, clarithromycin, erythromycin, josamycin, spiramycin, fidaxomicin, and ivermectin) on A. baumannii using a simple and newly established in vitro assay system for the swift and serial spectrophotometric determinations of two biofilm-amount indexes of viability and biomass. These macrolides were found to possess direct anti-biofilm effects exerting specific anti-biofilm effects not exclusively depending on their bacteriostatic/bactericidal effects. The anti-biofilm effect of azithromycin was found to be the strongest, while those of fidaxomicin and ivermectin were weak and limited. These results provide insights into possible adjunctive chemotherapy with macrolides for A. baumannii infection. Common five macrolides also interfered with the Agrobacterium tumefaciens NTL(pCF218) (pCF372) bioassay system of N-acyl homoserine lactones, providing insights into sample preparation for the bioassay, and putatively suggesting the actions of macrolides as remote signals in bacterial quorum sensing systems.

Bioengineered phytomolecules-capped silver nanoparticles using Carissa carandas leaf extract to embed on to urinary catheter to combat UTI pathogens

Rising incidents of urinary tract infections (UTIs) among catheterized patients is a noteworthy problem in clinic due to their colonization of uropathogens on abiotic surfaces. Herein, we have examined the surface modification of urinary catheter by embedding with eco-friendly synthesized phytomolecules-capped silver nanoparticles (AgNPs) to prevent the invasion and colonization of uropathogens. The preliminary confirmation of AgNPs production in the reaction mixture was witnessed by the colour change and surface resonance plasmon (SRP) band at 410nm by UV–visible spectroscopy. The morphology, size, crystalline nature, and elemental composition of attained AgNPs were further confirmed by the transmission electron microscopy (TEM), selected area electron diffraction (SAED), X-ray diffraction (XRD) technique, Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The functional groups of AgNPs with stabilization/capped phytochemicals were detected by Fourier-transform infrared spectroscopy (FTIR). Further, antibiofilm activity of synthesized AgNPs against biofilm producers such as Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa were determined by viability assays and micrographically. AgNPs coated and coating-free catheters performed to treat with bacterial pathogen to analyze the mat formation and disruption of biofilm formation. Synergistic effect of AgNPs with antibiotic reveals that it can enhance the activity of antibiotics, AgNPs coated catheter revealed that, it has potential antimicrobial activity and antibiofilm activity. In summary, C. carandas leaf extract mediated synthesized AgNPs will open a new avenue and a promising template to embed on urinary catheter to control clinical pathogens.

Effectiveness of topical adjuvants in reducing biofilm formation on orthopedic implants: an in vitro analysis

BACKGROUND AND HYPOTHESIS

The treatment of periprosthetic joint infection is complicated by the presence of residual biofilm, which resists eradication owing to bacterial adherence to orthopedic implants. The purpose of this study was to compare Bactisure (Zimmer Biomet, Warsaw, IN, USA), povidone-iodine (Betadine), and chlorhexidine gluconate solution (Irrisept; Irrimax, Gainesville, FL, USA) in reducing biofilm formation of Staphylococcus aureus, Staphylococcus epidermidis, and Cutibacterium acnes inoculated on cobalt-chrome, titanium, and stainless steel disks, representing metals commonly used for shoulder arthroplasty. The hypothesis was that there would be no significant difference in biofilm reduction among the 3 topical adjuvants.

METHODS

Strains of S aureus (ATCC 35556), S epidermidis (ATCC 35984), and C acnes (LMG 16711) were grown on cobalt-chrome, titanium, and stainless steel disks. For each strain, the disks were divided into 4 groups: (1) control, (2) povidone-iodine (Betadine), (3) chlorhexidine gluconate (Irrisept), and (4) Bactisure. Bacteria were grown on 5% sheep blood agar plates. Biofilm eradication was quantified using adenosine triphosphate bioluminescence and compared with controls 48 and 72 hours after implementation of the topical adjuvant.

RESULTS

At 72 hours after implementation of the topical adjuvant, a statistically significant reduction in colony-forming units was observed for all topical adjuvants across all tested metals, as compared with their respective control. With respect to the topical adjuvants themselves, Bactisure more consistently demonstrated the most significant reduction in colony-forming units across all bacteria when the tested medium was adjusted for, with the exception of S aureus, which showed similar results to Betadine at 72 hours.

CONCLUSION

By use of commonly encountered topical adjuvants on S aureus-, S epidermidis-, and C acnes-inoculated disks of various implant metals, a significant reduction in biofilm production was observed. Bactisure, a recent Food and Drug Administration-approved topical adjuvant, demonstrated the overall greatest efficacy of the agents studied.

Evaluation of biofilm colonization on multi-part dental implants in a rat model

BACKGROUND

Peri-implant mucositis and peri-implantitis are highly prevalent biofilm-associated diseases affecting the tissues surrounding dental implants. As antibiotic treatment is ineffective to fully cure biofilm mediated infections, antimicrobial modifications of implants to reduce or prevent bacterial colonization are called for. Preclinical in vivo evaluation of the functionality of new or modified implant materials concerning bacterial colonization and peri-implant health is needed to allow progress in this research field. For this purpose reliable animal models are needed.

METHODS

Custom made endosseous dental implants were installed in female Sprague Dawley rats following a newly established three-step implantation procedure. After healing of the bone and soft tissue, the animals were assigned to two groups. Group A received a continuous antibiotic treatment for 7 weeks, while group B was repeatedly orally inoculated with human-derived strains of Streptococcus oralis, Fusobacterium nucleatum and Porphyromonas gingivalis for six weeks, followed by 1 week without inoculation. At the end of the experiment, implantation sites were clinically assessed and biofilm colonization was quantified via confocal laser scanning microscopy. Biofilm samples were tested for presence of the administered bacteria via PCR analysis.

RESULTS

The inner part of the custom made implant screw could be identified as a site of reliable biofilm formation in vivo. S. oralis and F. nucleatum were detectable only in the biofilm samples from group B animals. P. gingivalis was not detectable in samples from either group. Quantification of the biofilm volume on the implant material revealed no statistically significant differences between the treatment groups. Clinical inspection of implants in group B animals showed signs of mild to moderate peri-implant mucositis (4 out of 6) whereas the mucosa of group A animals appeared healthy (8/8). The difference in the mucosa health status between the treatment groups was statistically significant (p = 0.015).

CONCLUSIONS

We developed a new rodent model for the preclinical evaluation of dental implant materials with a special focus on the early biofilm colonization including human-derived oral bacteria. Reliable biofilm quantification on the implant surface and the symptoms of peri-implant mucositis of the bacterially inoculated animals will serve as a readout for experimental evaluation of biofilm-reducing modifications of implant materials.

Microbial Biofilms in the Food Industry-A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.

A dynamic resazurin microassay allowing accurate quantification of cells and suitable for acid-forming bacteria

A resazurin micro-assay was developed to quantify acidifying bacteria. The resorufin fluorescent signal was measured over time and the determined time to reach the max slope (TMS) was plotted against CFU (colony forming unit) counts. This dynamic assay enabled to quantify nine lactic acid bacteria and a Bacillus licheniformis strain despite the increasing acidity of the medium.

The role of biofilm in the development and dissemination of ubiquitous pathogens in drinking water distribution systems: an overview of surveillance, outbreaks, and prevention

A variety of pathogenic microorganisms can survive in the drinking water distribution systems (DWDS) by forming stable biofilms and, thus, continually disseminating their population through the system's dynamic water bodies. The ingestion of the pathogen-contaminated water could trigger a broad spectrum of illnesses and well-being-related obstacles. These waterborne diseases are a significant concern for babies, pregnant women, and significantly low-immune individuals. This review highlights the recent advances in understanding the microbiological aspects of drinking water quality, biofilm formation and its dynamics, health issues caused by the emerging microbes in biofilm, and approaches for biofilm investigation its prevention and suppression in DWDS.

Material modifications enhancing the antibacterial properties of two biodegradable poly(3-hydroxybutyrate) implants

The aim of this study was to evaluate the antimicrobial efficacy of adding a gentamicin palmitate (GP) coating and zirconium dioxide (ZrO₂) to biodegradable poly(3-hydroxybutyrate) (PHB) to reduce biofilm formation. Cylindrical pins with and without a coating were incubated in Müller-Hinton broth inoculated with 2 × 10⁵ colony-forming units (CFU) ml-1 of Staphylococcus aureus for 2 d or 7 d, then sonicated to disrupt biofilms. Pure PHB (PHB + GP) and PHB pins with ZrO₂ added (PHBzr + GP) were coated with GP and compared with PHB pins lacking a coating (PHB). Cells (CFU) were counted to quantify the number of bacteria in the biofilm and a cell proliferation assay was employed to evaluate metabolic activity, and scanning electron microscopy (SEM) was performed to visualize the structure of the biofilm. After 2 d of incubation there were significantly more cells in biofilms on PHB pins than PHB + GP and PHBzr + GP pins (p < 0.0001), and cells in the sonication fluid obtained from GP-coated pins exhibited significantly lower metabolic activity than cells from uncoated PHB pins (p < 0.0001). After 7 d of incubation metabolic activity was lowest for PHBzr + GP, with significant differences between PHB and PHBzr + GP (p = 0.001). SEM revealed more cells attached to the surface, and more structured biofilms, on pins without a coating. Coating pins with GP significantly reduced early biofilm formation on PHB implants. This could lower the potential risk of surgical site infections when using PHB implants. Addition of ZrO₂ might further enhance the antibacterial properties. Such modification of the implant material should therefore be considered when developing new biodegradable PHB implants.

Study of the effects of mineral salts on the biofilm formation on polypropylene fibers using three quantification methods

The microbial biofilms are ubiquitous in nature and represent important biological entities that affect various aspects of human life. As such, they attracted considerable attention during last decades, with the factors affecting the biofilm development being among the frequently studied topics. In our work, the biofilm was cultivated on the surface of polypropylene fibers in a nutrient medium inoculated by the suspension of two unsterile soils. The effects of ionic strength and valence of salt on the amount of the produced biofilm and on composition of biofilm microbial communities were investigated. The effect of valence was significant in some OTUs: Arthrobacter/Pseudarthrobacter/Paenarthrobacter and Bacillus with positive response to monovalent salt (KCl) and Streptomyces, Lysinibacillus, Pseudomonas, and Ensifer with positive response to divalent salt (MgSO₄). The significant preference for a certain concentration of salts was observed in the case of OTUs Agrobacterium, Bacillus (both 100 mM), and Brevundimonas (30 mM). A new quantification method based on measuring of oxidizable organic carbon in biofilm biomass, based on dichromate oxidation, was used. We compared the results obtained using this method with results of crystal violet destaining and measuring of extracted DNA concentration as proxies of the biofilm biomass. The dichromate oxidation is simple, inexpensive, and fast, and our results show that it may be more sensitive than crystal violet destaining. The highest biomass values tended to associate with high concentrations of the divalent salt. This trend was not observed in treatments where the monovalent salt was added. Our data confirm the importance of inorganic ions for biofilm composition and biomass accumulation.

Inhibition of Angiotensin Converting Enzyme Impairs Anti-staphylococcal Immune Function in a Preclinical Model of Implant Infection

Background: Evidence suggests the renin-angiotensin system (RAS) plays key immunomodulatory roles. In particular, angiotensin-converting enzyme (ACE) has been shown to play a role in antimicrobial host defense. ACE inhibitors (ACEi) and angiotensin receptor blockers (ARB) are some of the most commonly prescribed medications, especially in patients undergoing invasive surgery. Thus, the current study assessed the immunomodulatory effect of RAS-modulation in a preclinical model of implant infection.

Methods:In vitro antimicrobial effects of ACEi and ARBs were first assessed. C57BL/6J mice subsequently received either an ACEi (lisinopril; 16 mg/kg/day), an ARB (losartan; 30 mg/kg/day), or no treatment. Conditioned mice blood was then utilized to quantify respiratory burst function as well as Staphylococcus aureus Xen36 burden ex vivo in each treatment group. S. aureus infectious burden for each treatment group was then assessed in vivo using a validated mouse model of implant infection. Real-time quantitation of infectious burden via bioluminescent imaging over the course of 28 days post-procedure was assessed. Host response via monocyte and neutrophil infiltration within paraspinal and spleen tissue was quantified by immunohistochemistry for F4/80 and myeloperoxidase, respectively.

Results: Blood from mice treated with an ACEi demonstrated a decreased ability to eradicate bacteria when mixed with Xen36 as significantly higher levels of colony forming units (CFU) and biofilm formation was appreciated ex vivo (p < 0.05). Mice treated with an ACEi showed a higher infection burden in vivo at all times (p < 0.05) and significantly higher CFUs of bacteria on both implant and paraspinal tissue at the time of sacrifice (p < 0.05 for each comparison). There was also significantly decreased infiltration and respiratory burst function of immune effector cells in the ACEi group (p < 0.05).

Conclusion: ACEi, but not ARB, treatment resulted in increased S. aureus burden and impaired immune response in a preclinical model of implant infection. These results suggest that perioperative ACEi use may represent a previously unappreciated risk factor for surgical site infection. Given the relative interchangeability of ACEi and ARB from a cardiovascular standpoint, this risk factor may be modifiable.

In Vitro Evaluation of the Antibacterial Properties of Tea Tree Oil on Planktonic and Biofilm-Forming Streptococcus mutans

Streptococcus mutans (S. mutans) is the principal etiologic agent in the occurrence of human dental caries and the formation of biofilms on the surface of teeth. Tea tree oil (TTO) has been demonstrated to exhibit a wide range of pharmacological actions that can effectively inhibit the activity of bacteria. In this context, we evaluated the in vitro antimicrobial effects of TTO on S. mutans both during planktonic growth and in biofilms compared with 0.2% CHX. We determined the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) using the microdilution method, the bacteriostatic rate using an MTT assay, and the antimicrobial time using a time-kill assay. Then, we explored the effects of TTO on acid production and cell integrity. Furthermore, the effects of TTO on the biomass and bacterial activity of S. mutans biofilms were studied. Finally, scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) were used to investigate the structure and activity of biofilms. The MIC and MBC values were 0.125% and 0.25%, and the bacterial inhibition rate was concentration dependent. TTO can effectively inhibit bacterial acid production and destroy the integrity of the cell membrane. Electron micrographs revealed a reduction in bacterial aggregation, inhibited biofilm formation, and reduced biofilm thickness. The effect of TTO was the same as that of 0.2% CHX at a specific concentration. In summary, we suggest that TTO is a potential anticariogenic agent that can be used against S. mutans.

Rapid, Noninvasive, and Nondestructive Method for Biofilm Imaging on Metallic Surfaces Using Active Thermography

A simple, rapid, low-cost method was proposed for the imaging of Pseudomonas aeruginosa biofilms on metallic surfaces using an infrared camera. Stainless steel coupons were cooled to generate a thermal gradient in relation to biofilm for active thermography (AT). Both cooling and image acquisition times were optimized and the images obtained with AT were compared with those from scanning electron microscopy. A free software (Thermofilm) was developed for image processing and the results were compared with the software ImageJ, with good agreement (from 87.7 to 103.8%). Images of coupons treated with sanitizer (peracetic acid) were obtained to show the applicability of the proposed method for biofilm studies. All analytical steps could be performed in 3 min in a noncontact, nondestructive, low-cost, portable, and easy-to-use way.

Increased Staphylococcus aureus Biofilm Formation on Biodegradable Poly(3-Hydroxybutyrate)-Implants Compared with Conventional Orthopedic Implants: An In Vitro Analysis

OBJECTIVE

To compare the biofilm formation on a biodegradable material, poly(3-hydroxybutyrate) (PHB), with that on conventional titanium (Ti) and steel (St) implant material.

METHODS

Pins made of the different materials were incubated in Müller-Hinton broth inoculated with 2 × 10 colony-forming units (CFU)·mL of Staphylococcus aureus for 2 and 7 days and then sonicated for the disruption of the biofilms. CFU were counted to quantify the number of bacteria in the biofilm, and the cell proliferation assay 2,3-Bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H- tetrazolium-5-carboxanilid salt was used to evaluate their metabolic activity. Scanning electron microscopy visualized the structure of the biofilm.

RESULTS

We found a significantly higher metabolic activity and CFU count in the biofilm of PHB pins compared with St and Ti pins (analysis of variance, P < 0.0001). Scanning electron microscopy revealed structured biofilms on PHB pins already after 2 days of incubation, which was not observed on the other tested implants.

CONCLUSION

PHB implants seem to provide an environment that advantages the formation of biofilms of S. aureus, a common pathogen in implant-related infections. The amount of biofilm is higher on PHB implant compared with conventionally used orthopedic titanium and steel implants. To overcome the potential risk of surgical site infections linked to the clinical use of PHB implants, possible modifications of the material, increasing its antibacterial properties, need to be further investigated.

Laser-structured spike surface shows great bone integrative properties despite infection in vivo

Implant associated infections can result in devastating consequences for patients. One major cause is the formation of bacterial biofilms, which result in increased resistance against antimicrobial therapeutics. A reduction of implant associated infections can be achieved by functionalization of implant surfaces. The generation of three dimensional surface structures by femtosecond laser ablation is one method to fabricate bacterial repellent large scaled surfaces without altering the material chemical composition. The challenge is to reduce bacterial growth while improving cellular ongrowth. For this purpose, spike structures were created as small as possible by used fabrication method on cubic Ti90/Al6/V4-rods and their effectiveness against bacterial colonization was compared to unstructured Ti90/Al6/V4-rods. Rods were implanted in the rat tibia and infected intraoperatively with 10³ CFU of Staphylococcus aureus. Besides clinical behaviour and lameness, the vital bacterial biomass, morphological appearance and the volume of eukaryotic cells were determined on the implant surface after 21 days. Bone alterations were examined by radiological and histological techniques. Unexpectedly, the laser-structured implants did not show a lower bacterial load on the implant surface and less severe infection related bone and tissue alterations compared to the group without structuring. Simultaneously, a better bony integration and a higher cellular colonization with eukaryotic cells was detected on the laser-structured implants. These findings don't support the previous in vitro results. Nevertheless, the strong integration into the bone is a powerful argument for further surface modifications focussing on the improvement of the antibacterial effect. Additionally, our results underline the need for in vivo testing of new materials prior to clinical use.

Differential Susceptibility of Catheter Biomaterials to Biofilm-Associated Infections and Their Remedy by Drug-Encapsulated Eudragit RL100 Nanoparticles

Biofilms are the cause of major bacteriological infections in patients. The complex architecture of Escherichia coli (E. coli) biofilm attached to the surface of catheters has been studied and found to depend on the biomaterial's surface properties. The SEM micrographs and water contact angle analysis have revealed that the nature of the surface affects the growth and extent of E. coli biofilm formation. In vitro studies have revealed that the Gram-negative E. coli adherence to implanted biomaterials takes place in accordance with hydrophobicity, i.e., latex > silicone > polyurethane > stainless steel. Permanent removal of E. coli biofilm requires 50 to 200 times more gentamicin sulfate (G-S) than the minimum inhibitory concentration (MIC) to remove 90% of E. coli biofilm (MBIC90). Here, in vitro eradication of biofilm-associated infection on biomaterials has been done by Eudragit RL100 encapsulated gentamicin sulfate (E-G-S) nanoparticle of range 140 nm. It is 10-20 times more effective against E. coli biofilm-associated infections eradication than normal unentrapped G-S. Thus, Eudragit RL100 mediated drug delivery system provides a promising way to reduce the cost of treatment with a higher drug therapeutic index.

Hydroxyl radicals generated by hydrogen peroxide photolysis recondition biofilm-contaminated titanium surfaces for subsequent osteoblastic cell proliferation

Titanium dental implants have been successfully used for decades; however, some implants are affected by peri-implantitis due to bacterial infection, resulting in loss of supporting bone. This study aimed to evaluate the effect of an antimicrobial chemotherapy employing H₂O₂ photolysis-developed to treat peri-implantitis-on biofilm-contaminated titanium surfaces in association with osteoblastic cell proliferation on the treated surface. Titanium discs were sandblasted and acid-etched, followed by contamination with a three-species biofilm composed of Porphyromonas gingivalis, Fusobacterium nucleatum, and Streptococcus mitis. This biofilm model was used as a simplified model of clinical peri-implantitis biofilm. The discs were subjected to ultrasound scaling, followed by H₂O₂ photolysis, wherein 365-nm LED irradiation of the disc immersed in 3% H₂O₂ was performed for 5 min. We analysed proliferation of mouse osteoblastic cells (MC3T3-E1) cultured on the treated discs. Compared with intact discs, biofilm contamination lowered cell proliferation on the specimen surface, whereas H₂O₂ photolysis recovered cell proliferation. Thus, H₂O₂ photolysis can recover the degraded biocompatibility of biofilm-contaminated titanium surfaces and can potentially be utilised for peri-implantitis treatment. However, to verify the findings of this study in relation to clinical settings, assessment using a more clinically relevant multi-species biofilm model is necessary.

Comparison of intraoral biofilm reduction on silver-coated and silver ion-implanted stainless steel bracket material : Biofilm reduction on silver ion-implanted bracket material

PURPOSE

The objective of this in situ study was to quantify the intraoral biofilm reduction on bracket material as a result of different surface modifications using silver ions. In addition to galvanic silver coating and physical vapor deposition (PVD), the plasma immersion ion implantation and deposition (PIIID) procedure was investigated for the first time within an orthodontic application.

MATERIALS AND METHODS

An occlusal splint equipped with differently silver-modified test specimens based on stainless steel bracket material was prepared for a total of 12 periodontally healthy patients and was worn in the mouth for 48 h. The initially formed biofilm was fluorescently stained and a quantitative comparative analysis of biofilm volume, biofilm surface coverage and live/dead distribution of bacteria was performed by confocal laser scanning microscopy (CLSM).

RESULTS

Compared to untreated stainless steel bracket material, the antibacterial effect of the PIIID silver-modified surface was just as significant with regard to reducing the biofilm volume and the surface coverage as the galvanically applied silver layer and the PVD silver coating. Regarding the live/dead distribution, however, the PIIID modification was the only surface that showed a significant increase in the proportion of dead cells compared to untreated bracket material and the galvanic coating.

CONCLUSIONS

Orthodontic stainless steel with a silver-modified surface by PIIID procedure showed an effective reduction in the intraoral biofilm formation compared to untreated bracket material, in a similar manner to PVD and galvanic silver coatings applied to the surface. Additionally, the PIIID silver-modified surface has an increased bactericidal effect.

Bacterial biofilm formation on implantable devices and approaches to its treatment and prevention

In living organisms, biofilms are defined as complex communities of bacteria residing within an exopolysaccharide matrix that adheres to a surface. In the clinic, they are typically the cause of chronic, nosocomial, and medical device-related infections. Due to the antibiotic-resistant nature of biofilms, the use of antibiotics alone is ineffective for treating biofilm-related infections. In this review, we present a brief overview of concepts of bacterial biofilm formation, and current state-of-the-art therapeutic approaches for preventing and treating biofilms. Also, we have reviewed the prevalence of such infections on medical devices and discussed the future challenges that need to be overcome in order to successfully treat biofilms using the novel technologies being developed.

Activity of a novel antimicrobial peptide against Pseudomonas aeruginosa biofilms

With the increasing recognition of biofilms in human disease, the development of novel antimicrobial therapies is of critical importance. For example, in patients with cystic fibrosis (CF), the acquisition of host-adapted, chronic Pseudomonas aeruginosa infection is associated with a decline in lung function and increased mortality. Our objective was to test the in vitro efficacy of a membrane-active antimicrobial peptide we designed, termed 6K-F17 (sequence: KKKKKK-AAFAAWAAFAA-NH₂), against multidrug resistant P. aeruginosa biofilms. This peptide displays high antimicrobial activity against a range of pathogenic bacteria, yet is non-hemolytic to human erythrocytes and non-toxic to human bronchial epithelial cells. In the present work, P. aeruginosa strain PAO1, and four multidrug resistant (MDR) isolates from chronically infected CF individuals, were grown as 48-hour biofilms in a static biofilm slide chamber model. These biofilms were then exposed to varying concentrations of 6K-F17 alone, or in the presence of tobramycin, prior to confocal imaging. Biofilm biovolume and viability were assessed. 6K-F17 was able to kill biofilms - even in the presence of sputum - and greatly reduce biofilm biovolume in PAO1 and MDR isolates. Strikingly, when used in conjunction with tobramycin, low doses of 6K-F17 significantly potentiated tobramycin killing, leading to biofilm destruction.

Influence of Probiotic Culture Supernatants on In Vitro Biofilm Formation of Staphylococci

Background

The effects of cell-free culture supernatants of probiotic Lactobacillus rhamnosus GG and Streptococcus salivarius K12 on replication and biofilm forming of Staphylococcus aureus and S. epidermidis were assessed in vitro.

Methods

S. aureus and S. epidermidis strains were exposed to cell-free culture supernatants of L. rhamnosus GG and S. salivarius K12 at different concentrations starting at 0, 4, and 24 h after the onset of incubation. Bacterial amplification was measured on microplate readers, as well as biofilm growth after safranine staining. Scanning electron microscopy was performed for visualization of biofilm status.

Results

The S. salivarius K12 culture supernatant not only reduced or prevented the formation and maturation of fresh biofilms but even caused a reduction of preformed S. epidermidis biofilms. The L. rhamnosus GG culture supernatant did not show clear inhibitory effects regardless of concentration or time of addition of supernatant, and even concentration-depending promotional effects on the planktonic and biofilm growth of S. aureus and S. epidermidis were observed.

Conclusion

In particular, the inhibitory effects of the S. salivarius K12 culture supernatant on the formation of staphylococcal biofilms are of potential relevance for biofilm-associated diseases and should be further assessed by in vivo infection models.