Antimicrobial penetration and efficacy in an in vitro oral biofilm model

Bacteriocins: potentials and prospects in health and agrifood systems

Bacteriocins are highly diverse, abundant, and heterogeneous antimicrobial peptides that are ribosomally synthesized by bacteria and archaea. Since their discovery about a century ago, there has been a growing interest in bacteriocin research and applications. This is mainly due to their high antimicrobial properties, narrow or broad spectrum of activity, specificity, low cytotoxicity, and stability. Though initially used to improve food quality and safety, bacteriocins are now globally exploited for innovative applications in human, animal, and food systems as sustainable alternatives to antibiotics. Bacteriocins have the potential to beneficially modulate microbiota, providing viable microbiome-based solutions for the treatment, management, and non-invasive bio-diagnosis of infectious and non-infectious diseases. The use of bacteriocins holds great promise in the modulation of food microbiomes, antimicrobial food packaging, bio-sanitizers and antibiofilm, pre/post-harvest biocontrol, functional food, growth promotion, and sustainable aquaculture. This can undoubtedly improve food security, safety, and quality globally. This review highlights the current trends in bacteriocin research, especially the increasing research outputs and funding, which we believe may proportionate the soaring global interest in bacteriocins. The use of cutting-edge technologies, such as bioengineering, can further enhance the exploitation of bacteriocins for innovative applications in human, animal, and food systems.

Absence of Synergism between a Dual-AMP Biogel and Antibiotics Used as Therapeutic Agents for Diabetic Foot Infections

Diabetic foot infections (DFIs) are frequently linked to diabetic-related morbidity and death because of the ineffectiveness of conventional antibiotics against multidrug-resistant bacteria. Pexiganan and nisin A are antimicrobial peptides (AMPs), and their application may complement conventional antibiotics in DFI treatment. A collagen 3D model, previously established to mimic a soft-tissue collagen matrix, was used to evaluate the antibacterial efficacy of a guar gum gel containing pexiganan and nisin alone and combined with three antimicrobials toward the biofilms of Staphylococcus aureus and Pseudomonas aeruginosa isolated from infected foot ulcers. Antimicrobials and bacterial diffusion were confirmed by spot-on-lawn and bacterial growth by bacterial count (cfu/mL). Our main conclusion was that the dual-AMP biogel combined with gentamicin, clindamycin, or vancomycin was not able to significantly reduce bacterial growth or eradicate S. aureus and P. aeruginosa DFI isolates. We further reported an antagonism between dual-AMP and dual-AMP combined with antibiotics against S. aureus.

Antimicrobial effect against Aggregatibacter actinomycetemcomitans of advanced and injectable platelet-rich fibrin from patients with periodontal diseases versus periodontally healthy subjects

Objectives

Advanced platelet-rich fibrin (A-PRF+) and injectable platelet-rich fibrin (i-PRF) have recently been developed and used in periodontal therapy. Few studies have contrasted the antibacterial effectiveness of these autologous materials derived from individuals with healthy gums, gingivitis, and periodontitis. This study aimed to compare the antimicrobial effects of these PRF materials against the periodontal pathogenic bacterium Aggregatibacter actinomycetemcomitans (Aa) in patients with different periodontal conditions.

Methods

Blood samples were collected from periodontally healthy individuals, patients with gingivitis, or patients with periodontitis to prepare A-PRF+ and i-PRF. The antibacterial capacity of these materials was evaluated through antibiofilm formation, biofilm susceptibility, and the time-kill assay over a 48-h period.

Results

A-PRF+ and i-PRF from each patient groups interfered with Aa's ability to form biofilm on the test tube surface, and the effect of i-PRF was significantly different among the patient groups. In contrast, these plasma preparation had a weak impact on mature biofilm. For products from the gingivitis and periodontitis groups, these effects were significantly stronger for i-PRF than A-PRF+ (p = 0.012 and p = 0.004, respectively). All plasma preparations inhibited Aa growth in the first 12 h after application, and i-PRF exhibited a significantly greater antimicrobial effect than A-PRF + at each time point.

Conclusion

A-PRF+ and i-PRF in all three patient groups could inhibit the growth of Aa in vitro, and i-PRF from patients with periodontitis exhibited a more significant effect than PRF from the other groups.

Effects of phosphate and silicate on stiffness and viscoelasticity of mature biofilms developed with simulated drinking water

Biofilms, a porous matrix of cells aggregated with extracellular polymeric substances under the influence of chemical constituents in the feed water, can develop a viscoelastic response to mechanical stresses. In this study, the roles of phosphate and silicate, common additives in corrosion control and meat processing, on the stiffness, viscoelasticity, porous structure networks, and chemical properties of biofilm were investigated. Three-year biofilms on PVC coupons were grown from sand-filtered groundwater with or without one of the non-nutrient (silicate) or nutrient additives (phosphate or phosphate blends). Compared with non-nutrient additives, the phosphate and phosphate-blend additives led to a biofilm with the lowest stiffness, most viscoelastic, and more porous structure, including more connecting throats with greater equivalent radii. The phosphate-based additives also led to more organic species in the biofilm matrix than the silicate additive did. This work demonstrated that nutrient additives could promote biomass accumulation but also reduce mechanical stability.

Advancements in antimicrobial nanoscale materials and self-assembling systems

Antimicrobial resistance is directly responsible for more deaths per year than either HIV/AIDS or malaria and is predicted to incur a cumulative societal financial burden of at least $100 trillion between 2014 and 2050. Already heralded as one of the greatest threats to human health, the onset of the coronavirus pandemic has accelerated the prevalence of antimicrobial resistant bacterial infections due to factors including increased global antibiotic/antimicrobial use. Thus an urgent need for novel therapeutics to combat what some have termed the 'silent pandemic' is evident. This review acts as a repository of research and an overview of the novel therapeutic strategies being developed to overcome antimicrobial resistance, with a focus on self-assembling systems and nanoscale materials. The fundamental mechanisms of action, as well as the key advantages and disadvantages of each system are discussed, and attention is drawn to key examples within each field. As a result, this review provides a guide to the further design and development of antimicrobial systems, and outlines the interdisciplinary techniques required to translate this fundamental research towards the clinic.

Effects of stabilized hypochlorous acid on oral biofilm bacteria

Background

Caries and periodontitis are amongst the most prevalent diseases worldwide, leading to pain and loss of oral function for those affected. Prevention relies heavily on mechanical removal of dental plaque biofilms but for populations where this is not achievable, alternative plaque control methods are required. With concerns over undesirable side-effects and potential bacterial resistance due to the use of chlorhexidine gluconate (CHX), new antimicrobial substances for oral use are greatly needed. Here we have investigated the antimicrobial effect of hypochlorous acid (HOCl), stabilized with acetic acid (HAc), on oral biofilms and compared it to that of CHX. Possible adverse effects of stabilized HOCl on hydroxyapatite surfaces were also examined.

Methods

Single- and mixed-species biofilms of six common oral bacteria (Streptococcus mutans, Streptococcus gordonii, Actinomyces odontolyticus, Veillonella parvula, Parvimonas micra and Porphyromonas gingivalis) within a flow-cell model were exposed to HOCl stabilized with 0.14% or 2% HAc, pH 4.6, as well as HOCl or HAc alone. Biofilm viability was assessed in situ using confocal laser scanning microscopy following LIVE/DEAD® BacLight™ staining. In-situ quartz crystal microbalance with dissipation (QCM-D) was used to study erosion of hydroxyapatite (HA) surfaces by stabilized HOCl.

Results

Low concentrations of HOCl (5 ppm), stabilized with 0.14% or 2% HAc, significantly reduced viability in multi-species biofilms representing supra- and sub-gingival oral communities, after 5 min, without causing erosion of HA surfaces. No equivalent antimicrobial effect was seen for CHX. Gram-positive and Gram-negative bacteria showed no significant differential suceptibility to stabilized HOCl.

Conclusions

At low concentrations and with exposure times which could be achieved through oral rinsing, HOCl stabilized with HAc had a robust antimicrobial activity on oral biofilms, without causing erosion of HA surfaces or affecting viability of oral keratinocytes. This substance thus appears to offer potential for prevention and/or treatment of oral biofilm-mediated diseases.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02453-2.

Evidence on the Use of Mouthwash for the Control of Supragingival Biofilm and Its Potential Adverse Effects

Antimicrobial mouthwash improves supragingival biofilm control when used in conjunction with mechanical removal as part of an oral hygiene routine. Mouthwash is intended to suppress bacterial adhesion during biofilm formation processes and is not aimed at mature biofilms. The most common evidence-based effects of mouthwash on the subgingival biofilm include the inhibition of biofilm accumulation and its anti-gingivitis property, followed by its cariostatic activities. There has been no significant change in the strength of the evidence over the last decade. A strategy for biofilm control that relies on the elimination of bacteria may cause a variety of side effects. The exposure of mature oral biofilms to mouthwash is associated with several possible adverse reactions, such as the emergence of resistant strains, the effects of the residual structure, enhanced pathogenicity following retarded penetration, and ecological changes to the microbiota. These concerns require further elucidation. This review aims to reconfirm the intended effects of mouthwash on oral biofilm control by summarizing systematic reviews from the last decade and to discuss the limitations of mouthwash and potential adverse reactions to its use. In the future, the strategy for oral biofilm control may shift to reducing the biofilm by detaching it or modulating its quality, rather than eliminating it, to preserve the benefits of the normal resident oral microflora.

Oral Microbiome: Getting to Know and Befriend Neighbors, a Biological Approach

The oral microbiome, forming a biofilm that covers the oral structures, contains a high number of microorganisms. Biofilm formation starts from the salivary pellicle that allows bacterial adhesion-colonization-proliferation, co-aggregation and biofilm maturation in a complex microbial community. There is a constant bidirectional crosstalk between human host and its oral microbiome. The paper presents the fundamentals regarding the oral microbiome and its relationship to modulator factors, oral and systemic health. The modern studies of oral microorganisms and relationships with the host benefits are based on genomics, transcriptomics, proteomics and metabolomics. Pharmaceuticals such as antimicrobials, prebiotics, probiotics, surface active or abrasive agents and plant-derived ingredients may influence the oral microbiome. Many studies found associations between oral dysbiosis and systemic disorders, including autoimmune diseases, cardiovascular, diabetes, cancers and neurodegenerative disorders. We outline the general and individual factors influencing the host-microbial balance and the possibility to use the analysis of the oral microbiome in prevention, diagnosis and treatment in personalized medicine. Future therapies should take in account the restoration of the normal symbiotic relation with the oral microbiome.

In vitro model systems for exploring oral biofilms: From single-species populations to complex multi-species communities

Numerous in vitro biofilm model systems are available to study oral biofilms. Over the past several decades, increased understanding of oral biology and advances in technology have facilitated more accurate simulation of intraoral conditions and have allowed for the increased generalizability of in vitro oral biofilm studies. The integration of contemporary systems with confocal microscopy and 16S rRNA community profiling has enhanced the capabilities of in vitro biofilm model systems to quantify biofilm architecture and analyse microbial community composition. In this review, we describe several model systems relevant to modern in vitro oral biofilm studies: the constant depth film fermenter, Sorbarod perfusion system, drip-flow reactor, modified Robbins device, flowcells and microfluidic systems. We highlight how combining these systems with confocal microscopy and community composition analysis tools aids exploration of oral biofilm development under different conditions and in response to antimicrobial/anti-biofilm agents. The review closes with a discussion of future directions for the field of in vitro oral biofilm imaging and analysis.

A critical analysis of research methods and experimental models to study intracanal medicaments

In order to ensure predictable decontamination of the root canal system, chemo-mechanical preparation of the root canal space is sometimes supplemented with the use of intracanal medication. As microbial control of the root canal space is fundamental to the resolution of apical periodontitis, root canal disinfection strategies haven been researched intensively. The use of intracanal medication as a supplementary step to the chemo-mechanical preparation of the root canal space is one of them. Because of the costs and limitations of clinical research it is relevant and common practice to first evaluate alternative or new root canal disinfection modalities in laboratory studies. This involves the simulation of a root canal infection in a laboratory model, on which different disinfection strategies can be tested. When modelling the infected root canal, different levels of infection can be discriminated: suspended bacteria, microbial biofilms and infected dentine. This review describes the experimental models associated with these infection levels and critically appraises their value and methodological details. Suggestions for relevant research methods and experimental models are given, as well as some good practices for laboratory-based microbiological studies.

Antimicrobial Mechanisms of Leucocyte- and Platelet Rich Fibrin Exudate Against Planktonic Porphyromonas gingivalis and Within Multi-Species Biofilm: A Pilot Study

Leucocyte- and platelet rich fibrin (L-PRF) is an autologous biomaterial used in regenerative procedures. It has an antimicrobial activity against P. gingivalis although the mechanism is not fully understood. It was hypothesized that L-PRF exudate releases hydrogen peroxide and antimicrobial peptides that inhibit P. gingivalis growth. Agar plate and planktonic culture experiments showed that the antimicrobial effect of L-PRF exudate against P. gingivalis was supressed by peroxidase or pepsin exposure. In developing multi-species biofilms, the antimicrobial effect of L-PRF exudate was blocked only by peroxidase, increasing P. gingivalis growth with 1.3 log genome equivalents. However, no effect was shown on other bacteria. Pre-formed multi-species biofilm trials showed no antimicrobial effect of L-PRF exudate against P. gingivalis or other species. Our findings showed that L-PRF exudate may release peroxide and peptides, which may be responsible for its antimicrobial effect against P. gingivalis. In addition, L-PRF exudate had an antimicrobial effect against P. gingivalis in an in vitro developing multi-species biofilm.

A Bioengineered Nisin Derivative To Control Streptococcus uberis Biofilms

Antimicrobial peptides are evolving as novel therapeutic options against the increasing problem of multidrug-resistant microorganisms, and nisin is one such avenue. However, some bacteria possess a specific nisin resistance system (NSR), which cleaves the peptide reducing its bactericidal efficacy. NSR-based resistance was identified in strains of Streptococcus uberis, a ubiquitous pathogen that causes mastitis in dairy cattle. Previous studies have demonstrated that a nisin A derivative termed nisin PV, featuring S29P and I30V, exhibits enhanced resistance to proteolytic cleavage by NSR. Our objective was to investigate the ability of this nisin derivative to eradicate and inhibit biofilms of S. uberis DPC 5344 and S. uberis ATCC 700407 (nsr⁺) using crystal violet (biomass), 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) (viability) assays, and confocal microscopy (viability and architecture). When preestablished biofilms were assessed, both peptides reduced biofilm biomass by over 60% compared to that of the untreated controls. However, a 42% higher reduction in viability was observed following treatment with nisin PV compared to that of nisin A. Accordingly, confocal microscopy analysis revealed significantly more dead cells on the biofilm upper surface and a reduced thickness following treatment with nisin PV. When biofilm inhibition was assessed, nisin PV inhibited biofilm formation and decreased viability up to 56% and 85% more than nisin A, respectively. Confocal microscopy analysis revealed a lack of biofilm for S. uberis ATCC 700407 and only dead cells for S. uberis DPC 5344. These results suggest that nisin PV is a promising alternative to effectively reduce the biofilm formation of S. uberis strains carrying NSR. IMPORTANCE One of the four most prevalent species of bovine mastitis-causing pathogens is S. uberis. Its ability to form biofilms confers on the bacteria greater resistance to antibiotics, requiring higher doses to be more effective. In a bid to limit antibiotic resistance development, the need for alternative antimicrobials is paramount. Bacteriocins such as nisin represent one such alternative that could alleviate the impact of mastitis caused by S. uberis. However, many strains of S. uberis have been shown to possess nisin resistance determinants, such as the nisin resistance protein (NSR). In this study, we demonstrate the ability of nisin and a nisin derivative termed PV that is insensitive to NSR to prevent and remove biofilms of NSR-producing S. uberis strains. These findings will add new information to the antimicrobial bacteriocins and control of S. uberis research fields specifically in relation to biofilms and nsr⁺ mastitis-associated strains.

Development of a herbal mouthwash containing a mixture of essential oils and plant extracts and in vitro testing of its antimicrobial efficiency against the planktonic and biofilm-enclosed cariogenic bacterium Streptococcus mutans

A herbal mouthwash containing essential oils of holy basil and mountain tea, extracts of St John's wort and European goldenrod (Bucovia™) and cetylpyridinium chloride, was developed and in vitro tested for its efficiency against biofilm formation by Streptococcus mutans, together with its eradicating activity against already preformed (48 h with saccharose) streptococcal biofilm. The minimum inhibitory (MIC) and bactericidal concentrations (MBC) of the final formulation, as well as of its individual components, were initially determined. The results revealed that the mouthwash needed to be applied at two-times its MIC (0.63% v.v^-1) to completely inhibit biofilm formation by S. mutans, which was otherwise capable of developing a robust biofilm on the tested surface. Once fully developed, the matrix of the biofilm was found to contain a significant amount of exopolysaccharides protecting the cells, being impossible to eradicate even when exposed to pure mouthwash for 15 min, highlighting the great recalcitrance of biofilm-embedded S. mutans.

The dual anti-caries effect of carboxymethyl chitosan nanogel loaded with chimeric lysin ClyR and amorphous calcium phosphate

In this study, we evaluated the anti-biofilm and anti-demineralization abilities of a novel material, CMC-ClyR-ACP nanogel, designed by loading the chimeric lysin ClyR and amorphous calcium phosphate (ACP) into a nanocarrier material carboxymethyl chitosan (CMC), in a demineralization model. Dynamic light scattering, transmission electron microscopy, and Fourier transmission infrared spectroscopy showed that CMC-ClyR-ACP nanogel was synthesized successfully. Enamel samples prepared from premolars were divided into five groups according to their treatments with: (i) double distilled water ddH₂ O, (ii) CMC-ACP, (iii) CMC-ClyR-ACP, (iv) ClyR, or (v) 0.12% chlorhexidine. Streptococcus mutans was allowed to form biofilms on the teeth for two days before treatment procedures were carried out from day 3 to day 6. The relative biofilm viability analyzed by Cell Counting Kit-8 showed that it was significantly lower (at 55.7%) for CMC-ClyR-ACP than seen for ddH₂ O (89.9%), which was consistent with result of confocal laser scanning microscopy. The percentage surface hardness loss of CMC-ClyR-ACP (29.2%) was significantly lower than that of CMC-ACP (51.0%) and ClyR (58.7%) alone, and there was no significant difference between CMC-ClyR-ACP and chlorhexidine (26.9%), which was confirmed by scanning electron microscopy. Therefore, CMC-ClyR-ACP nanogel may be an effective strategy for the control of enamel demineralization.

Modeling of Symbiotic Bacterial Biofilm Growth with an Example of the Streptococcus-Veillonella sp. System

We present a multi-dimensional continuum mathematical model for modeling the growth of a symbiotic biofilm system. We take a dual-species namely, the Streptococcus-Veillonella sp. biofilm system as an example for numerical investigations. The presented model describes both the cooperation and competition between these species of bacteria. The coupled partial differential equations are solved by using an integrative finite element numerical strategy. Numerical examples are carried out for studying the evolution and distribution of the bio-components. The results demonstrate that the presented model is capable of describing the symbiotic behavior of the biofilm system. However, homogenized numerical solutions are observed locally. To study the homogenization behavior of the model, numerical investigations regarding on how random initial biomass distribution influences the homogenization process are carried out. We found that a smaller correlation length of the initial biomass distribution leads to faster homogenization of the solution globally, however, shows more fluctuated biomass profiles along the biofilm thickness direction. More realistic scenarios with bacteria in patches are also investigated numerically in this study.

Antimicrobial stewardship of antiseptics that are pertinent to wounds: the need for a united approach

Long before the nature of infection was recognized, or the significance of biofilms in delayed healing was understood, antimicrobial agents were being used in wound care. In the last 70 years, antibiotics have provided an effective means to control wound infection, but the continued emergence of antibiotic-resistant strains and the documented antibiotic tolerance of biofilms has reduced their effectiveness. A range of wound dressings containing an antimicrobial (antibiotic or non-antibiotic compound) has been developed. Whereas standardized methods for determining the efficacy of non-antibiotic antimicrobials in bacterial suspension tests were developed in the early twentieth century, standardized ways of evaluating the efficacy of antimicrobial dressings against microbial suspensions and biofilms are not available. Resistance to non-antibiotic antimicrobials and cross-resistance with antibiotics has been reported, but consensus on breakpoints is absent and surveillance is impossible. Antimicrobial stewardship is therefore in jeopardy. This review highlights these difficulties and in particular the efficacy of current non-antibiotic antimicrobials used in dressings, their efficacy, and the challenges of translating in vitro efficacy data to the efficacy of dressings in patients. This review calls for a unified approach to developing standardized methods of evaluating antimicrobial dressings that will provide an improved basis for practitioners to make informed choices in wound care.

Staphylococcal Biofilms: Challenges and Novel Therapeutic Perspectives

Staphylococci, like Staphylococcus aureus and S. epidermidis, are common colonizers of the human microbiota. While being harmless in many cases, many virulence factors result in them being opportunistic pathogens and one of the major causes of hospital-acquired infections worldwide. One of these virulence factors is the ability to form biofilms-three-dimensional communities of microorganisms embedded in an extracellular polymeric matrix (EPS). The EPS is composed of polysaccharides, proteins and extracellular DNA, and is finely regulated in response to environmental conditions. This structured environment protects the embedded bacteria from the human immune system and decreases their susceptibility to antimicrobials, making infections caused by staphylococci particularly difficult to treat. With the rise of antibiotic-resistant staphylococci, together with difficulty in removing biofilms, there is a great need for new treatment strategies. The purpose of this review is to provide an overview of our current knowledge of the stages of biofilm development and what difficulties may arise when trying to eradicate staphylococcal biofilms. Furthermore, we look into promising targets and therapeutic methods, including bacteriocins and phage-derived antibiofilm approaches.

Bacteriocin-a potential antimicrobial peptide towards disrupting and preventing biofilm formation in the clinical and environmental locales

Biofilm, a consortium of microbial cells, protected by extracellular polymeric matrix, is considered a global challenge due to the inherent antibiotic resistance conferred by its lifestyle. Besides, it poses environmental threats causing huge damage in food industries, fisheries, refineries, water systems, pharmaceutical industries, medical industries, etc. Living in a community of microbial populations is most critical in the clinical field, making it responsible for about 80% of severe and chronic microbial diseases. The necessity to find an alternative approach is the need of the hour to solve these crises. So far, many approaches have been attempted to disrupt the initial stage of biofilm formation, including adherence and maturation. Bacteriocins are a group of antimicrobial peptides, produced by bacteria having the potential to disrupt biofilm either by itself or in combination with other drugs than antibiotic counterparts. A clear understanding on mechanisms of bacterial biofilm formation, progression, and resistance will surely lead to the development of innovative, effective biofilm control strategies in pharmaceutical, health care industries and environmental locales.

Sulfated vizantin causes detachment of biofilms composed mainly of the genus Streptococcus without affecting bacterial growth and viability

BACKGROUND

Sulfated vizantin, a recently developed immunostimulant, has also been found to exert antibiofilm properties. It acts not as a bactericide, but as a detachment-promoting agent by reducing the biofilm structural stability. This study aimed to investigate the mechanism underlying this activity and its species specificity using two distinct ex vivo oral biofilm models derived from human saliva.

RESULTS

The biofilm, composed mainly of the genus Streptococcus and containing 50 μM of sulfated vizantin, detached significantly from its basal surface with rotation at 500 rpm for only 15 s, even when 0.2% sucrose was supplied. Expression analyses for genes associated with biofilm formation and bacterial adhesion following identification of the Streptococcus species, revealed that a variety of Streptococcus species in a cariogenic biofilm showed downregulation of genes encoding glucosyltransferases involved in the biosynthesis of water-soluble glucan. The expression of some genes encoding surface proteins was also downregulated. Of the two quorum sensing systems involved in the genus Streptococcus, the expression of luxS in three species, Streptococcus oralis, Streptococcus gordonii, and Streptococcus mutans, was significantly downregulated in the presence of 50 μM sulfated vizantin. Biofilm detachment may be facilitated by the reduced structural stability due to these modulations. As a non-specific reaction, 50 μM sulfated vizantin decreased cell surface hydrophobicity by binding to the cell surface, resulting in reduced bacterial adherence.

CONCLUSION

Sulfated vizantin may be a candidate for a new antibiofilm strategy targeting the biofilm matrix while preserving the resident microflora.

Pexiganan in Combination with Nisin to Control Polymicrobial Diabetic Foot Infections

Diabetic foot ulcers (DFUs) are major complications of Diabetes mellitus being responsible for significant morbidity and mortality. DFUs frequently become chronically infected by a complex community of bacteria, including multidrug-resistant and biofilm-producing strains of Staphylococcus aureus and Pseudomonas aeruginosa. Diabetic foot infections (DFI) are often recalcitrant to conventional antibiotics and alternative treatment strategies are urgently needed. Antimicrobial Peptides (AMPs), such as pexiganan and nisin, have been increasingly investigated and reported as effective antimicrobial agents. Here, we evaluated the antibacterial potential of pexiganan and nisin used in combination (dual-AMP) to control the growth of planktonic and biofilm co-cultures of S. aureus and P. aeruginosa clinical strains, co-isolated from a DFU. A DFU collagen three-dimensional (3D) model was used to evaluate the distribution and efficacy of AMPs locally delivered into the model. The concentration of pexiganan required to inhibit and eradicate both planktonic and biofilm-based bacterial cells was substantially reduced when used in combination with nisin. Moreover, incorporation of both AMPs in a guar gum delivery system (dual-AMP biogel) did not affect the dual-AMP antimicrobial activity. Importantly, the application of the dual-AMP biogel resulted in the eradication of the S. aureus strain from the model. In conclusion, data suggest that the local application of the dual-AMPs biogel constitutes a potential complementary therapy for the treatment of infected DFU.

Therapeutic Potential of Bauhinia forficata Link in Dental Biofilm Treatment

The oral cytotoxicity, antimicrobial and anti-demineralizing effects of a tincture from Bauhinia forficata Link tincture (BFLT) were evaluated in vitro and ex vivo. Susceptibility tests (minimum inhibitory and microbicidal concentrations-MIC and time-kill assay-MMC) were performed against planktonic oral microorganisms. The contents of phenolic compounds were investigated. Cytotoxic potential was evaluated on oral fibroblasts after 1-5 min exposure to BFLT. Blocks of sound bovine enamel (N = 60) were inoculated with a saliva pool and sustained in a multiple plaque growth system for 48 h to form a biofilm. Biofilm blocks were randomly divided into groups-G (n = 10): G1-Baseline (48 h maturation biofilm), G2-BFLT 23.2 mg/mL, G3-Ethanol 81.20 g/mL, G4-Chlorhexidine 0.12%, G5-Growth control, and G6-Blank control. Treatments (50 μL/1 min) were performed once a day for a week. Streptococcus spp. (S) and total microorganism (TM) counts were expressed as Log₁₀ CFU/mL. Biofilm height was evaluated by confocal microscopy analyses (CMA). Final surface hardness was assessed and percentage of microhardness loss (% MHL) was calculated. Results were significant when P < .05. BFLT inhibited all tested microorganisms (MIC = 1.3-23.2 mg/mL) and promoted optical reduction (0.05-0.22 nm) of all microorganisms after 48-h treatment compared with controls. After 5-min treatment, BFLT showed low values of cell death (3.20%). G2-BFLT reduced S (6.61 ± 0.20) and TM (7.14 ± 0.38) compared with G1-Baseline (S = 7.82 ± 0.28; TM = 8.81 ± 0.67) and G5-Growth control (S = 7.48 ± 0.39; TM = 7.89 ± 0.68); but G4-chlororexidine (S = 6.11 ± 0.48; TM = 6.45 ± 0.16) showed the highest antibiofilm activity. CMA was not different among treatment groups. G2 showed lower % MHL compared with G5, although G4 presented the lowest. Results suggest BFLT is beneficial against dental caries, showing antimicrobial effects against a mature dental biofilm and no cytotoxicity.

Laser-induced vapor nanobubbles improve diffusion in biofilms of antimicrobial agents for wound care

Being responsible for delayed wound healing, the presence of biofilms in infected wounds leads to chronic, and difficult to treat infections. One of the reasons why antimicrobial treatment often fails to cure biofilm infections is the reduced penetration rate of antibiotics through dense biofilms. Strategies that have the ability to somehow interfere with the integrity of biofilms and allowing a better penetration of drugs are highly sought after. A promising new approach is the use of laser-induced vapor nanobubbles (VNB), of which it was recently demonstrated that it can substantially enhance the penetration of antibiotics into biofilms, resulting in a marked improvement of the killing efficiency. In this study, we examined if treatment of biofilms with laser-induced vapor nanobubbles (VNB) can enhance the potency of antimicrobials which are commonly used to treat wound infections, including povidone-iodine, chlorhexidine, benzalkonium chloride, cetrimonium bromide and mupirocin. Our investigations were performed on Pseudomonas aeruginosa and Staphylococcus aureus biofilms, which are often implicated in chronic wound infections. Pre-treatment of biofilms with laser-induced VNB did enhance the killing efficiency of those antimicrobials which experience a diffusion barrier in the biofilms, while this was not the case for those compounds for which there is no diffusion barrier. The magnitude of the enhanced potency was in most cases similar to the enhancement that was obtained when the biofilms were completely disrupted by vortexing and sonication. These results show that laser-induced VNB are indeed a very efficient way to enhance drug penetration deep into biofilms, and pave the way towards clinical translation of this novel approach for treatment of wound infections.

Antibacterial Surface Coating for Bone Scaffolds Based on the Dark Catalytic Effect of Titanium Dioxide

Biomaterials which promote tissue integration and resist microbial colonisation are required in bone tissue engineering to prevent biomaterial-associated infections. Surface modification of established materials for bone tissue engineering, such as TiO₂, have emerged as promising anti-infective strategies. Interestingly, the antibacterial activity of TiO₂ in the form of particles can be enhanced by combining it with H₂O₂, even in the absence of irradiation. However, it remains unknown whether TiO₂ surfaces elicit a similar effect. In this study, the antibacterial effect of porous TiO₂ scaffolds generated by the catalytic decomposition of H₂O₂ in the absence of light (dark catalysis) was investigated. Porous ceramic foams were fabricated and sol-gel coated for high catalytic activity. Degradation of methylene blue in the presence of 3% H₂O₂ increased by 80% for the sol-gel-coated surfaces. The degradation kinetics indicate that intermediate free radicals that form at the liquid-TiO₂ interface are responsible for the oxidative behavior of the surface. TiO₂ surfaces were further pretreated with 30% H₂O₂ for prolonged oxidative behavior. The biological response toward such surfaces was assessed in vitro. S. epidermidis biofilms formed on modified surfaces showed reduced viability compared to nonmodified surfaces. Further, the same surface modification showed no cytotoxic effects on MC3T3 preosteoblasts. However, the results from the conducted genotoxicity assay were inconclusive, and further studies are needed to exclude ROS-mediated DNA damage. To conclude, this study provides evidence that a simple surface modification based on the dark catalytic effect of TiO₂ can be used to create antibacterial surface properties for ceramic bone scaffolds.

Activity of the Chimeric Lysin ClyR against Common Gram-Positive Oral Microbes and Its Anticaries Efficacy in Rat Models

Dental caries is a common disease caused by oral bacteria. Streptococcus mutans and Streptococcus sobrinus are the primary cariogenic microbes that often survive as biofilms on teeth. In this study, we evaluated the activity of ClyR, a well-known chimeric lysin with extended streptococcal host range, against common Gram-positive oral microbes and its anticaries efficacy in rat models. ClyR demonstrated high lytic activity against S. mutans MT8148 and S. sobrinus ATCC6715, with minor activity against Streptococcus sanguinis, Streptococcus oralis, and Streptococcus salivarius, which are considered as harmless commensal oral bacteria. Confocal laser scanning microscopy showed that the number of viable cells in 72-h aged S. mutans and S. sobrinus biofilms are significantly (p < 0.05) decreased after treatment with 50 µg/mL ClyR for 5 min. Furthermore, continuous administration of ClyR for 40 days (5 µg/day) significantly (p < 0.05) reduced the severity of caries in rat models infected with a single or a mixed bacteria of S. mutans and S. sobrinus. Therefore, ClyR could be a promising agent or additive for the prevention and treatment of dental caries.

In vitro antibacterial and cytotoxic activities of carvacrol and terpinen-4-ol against biofilm formation on titanium implant surfaces

This study evaluated the antibacterial properties of carvacrol and terpinen-4-ol against Porphyromonas gingivalis and Fusobacterium nucleatum and its cytotoxic effects on fibroblast cells. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were examined. The minimum biofilm inhibition concentration (MBIC) was evaluated by XTT assay. Biofilm decontamination on titanium surfaces was quantified (CFU ml^-1), evaluated by confocal laser scanning microscopy (CLSM) and cytotoxic activity by MTT. The MIC and MBC for carvacrol were 0.007% and 0.002% for P. gingivalis and F. nucleatum, and 0.06% for terpinen-4-ol for both microorganisms. The MBIC for carvacrol was 0.03% and 0.06% for P. gingivalis and F. nucleatum, and for terpinen-4-ol was 0.06% and 0.24%. The results indicated anti-biofilm activity using carvacrol (0.26%, 0.06%) and terpinen-4-ol (0.95%, 0.24%) and showed cytotoxic activity similar to chlorohexidine (CHX). However, terpinen-4-ol (0.24%) showed higher cell viability than other treatments. Carvacrol and terpinen-4-ol showed antibacterial activity in respect of reducing biofilms. Moreover, CHX-like cytotoxicity was observed.

Fighting biofilms with lantibiotics and other groups of bacteriocins

Biofilms are sessile communities of bacteria typically embedded in an extracellular polymeric matrix. Bacterial cells embedded in biofilms are inherently recalcitrant to antimicrobials, compared to cells existing in a planktonic state, and are notoriously difficult to eradicate once formed. Avenues to tackle biofilms thus far have largely focussed on attempting to disrupt the initial stages of biofilm formation, including adhesion and maturation of the biofilm. Such an approach is advantageous as the concentrations required to inhibit formation of biofilms are generally much lower than removing a fully established biofilm. The crisis of antibiotic resistance in clinical settings worldwide has been further exacerbated by the ability of certain pathogenic bacteria to form biofilms. Perhaps the most notorious biofilm formers described from a clinical viewpoint have been methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa, Gardnerella vaginalis and Streptococcus mutans, the latter of which is found in oral biofilms. Due to the dearth of novel antibiotics in recent decades, compounded by the increasing rate of emergence of resistance amongst pathogens with a propensity for biofilm formation, solutions are urgently required to mitigate these crises. Bacteriocins are a class of antimicrobial peptides, which are ribosomally synthesised and often are more potent than their antibiotic counterparts. Here, we review a selection of studies conducted with bacteriocins with the ultimate objective of inhibiting biofilms. Overall, a deeper understanding of the precise means by which a biofilm forms on a substrate as well as insights into the mechanisms by which bacteriocins inhibit biofilms is warranted.

Zosteric acid and salicylic acid bound to a low density polyethylene surface successfully control bacterial biofilm formation

The active moieties of the anti-biofilm natural compounds zosteric (ZA) and salicylic (SA) acids have been covalently immobilized on a low density polyethylene (LDPE) surface. The grafting procedure provided new non-toxic eco-friendly materials (LDPE-CA and LDPE-SA) with anti-biofilm properties superior to the conventional biocide-based approaches and with features suitable for applications in challenging fields where the use of antimicrobial agents is limited. Microbiological investigation proved that LDPE-CA and LDPE-SA: (1) reduced Escherichia coli biofilm biomass by up to 61% with a mechanism that did not affect bacterial viability; (2) significantly affected biofilm morphology, decreasing biofilm thickness, roughness, substratum coverage, cell and matrix polysaccharide bio-volumes by >80% and increasing the surface to bio-volume ratio; (3) made the biofilm more susceptible to ampicillin and ethanol. Since no molecules were leached from the surface, they remained constantly effective and below the lethal level; therefore, the risk of inducing resistance was minimized.

Biofilm formation by the oral pioneer colonizer Streptococcus gordonii: an experimental and numerical study

For decades, extensive research efforts have been conducted to improve the functionality and stability of implants. Especially in dentistry, implant treatment has become a standard medical practice. The treatment restores full dental functionality, helping patients to maintain high quality of life. However, about 10% of the patients suffer from early and late device failure due to peri-implantitis, an inflammatory disease of the tissues surrounding the implant. Peri-implantitis is caused by progressive microbial colonization of the device surface and the formation of microbial communities, so-called biofilms. This infection can ultimately lead to implant failure. The causative agents for the inflammatory disease, periodontal pathogenic biofilms, have already been extensively studied, but are still not completely understood. As numerical simulations will have the potential to predict oral biofilm formation precisely in the future, for the first time, this study aimed to analyze Streptococcus gordonii biofilms by combining experimental studies and numerical simulation. The study demonstrated that numerical simulation was able to precisely model the influence of different nutrient concentration and spatial distribution of active and inactive biomass of the biofilm in comparison with the experimental data. This model may provide a less time-consuming method for the future investigation of any bacterial biofilm.

Low density polyethylene functionalized with antibiofilm compounds inhibits Escherichia coli cell adhesion

The present work concerns an efficient strategy to obtain novel medical devices materials able to inhibit biofilm formation. The new materials were achieved by covalent grafting of p-aminocinnamic or p-aminosalicylic acids on low density polyethylene coupons. The polyethylene surface, previously activated by oxygen plasma treatment, was functionalized using 2-hydroxymethylmetacrylate as linker. The latter was reacted with succinic anhydride affording the carboxylic end useful for the immobilization of the antibiofilm molecules. The modified surface was characterized by scanning electron microscope, X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform infrared and fluorescence analyses. The antibiofilm activity of the modified materials were tested against Escherichia coli biofilm grown in the Center of Disease Control biofilm reactor. The results revealed that the grafted cinnamic and salicylic acid derivatives reduced biofilm biomass, in comparison with the control, by 73.7 ± 10.7% and 63.4 ± 7.1%, respectively. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3251-3261, 2017.

Erythritol/chlorhexidine combination reduces microbial biofilm and prevents its formation on titanium surfaces in vitro

BACKGROUND

The purpose of this in vitro study was to evaluate the antibiofilm activity of a novel air-polishing powder consisting of erythritol and chlorhexidine, assessing its ability to reduce previously grown microbial biofilm and to prevent biofilm formation on titanium surfaces.

METHODS

Clinical strains of Staphylococcus aureus, Pseudomonas aeruginosa, Bacteroides fragilis and Candida albicans isolated from peri-implantitis lesions were used. Biofilm was grown on sandblasted titanium discs and treated with erythritol/chlorhexidine. The antimicrobial activity was evaluated by determining the minimum inhibitory concentration and the minimum microbicidal concentration. The antibiofilm activity was assessed by semiquantitative spectrophotometric assay and by confocal laser scanning microscopy.

RESULTS

Erythritol/chlorhexidine displayed an inhibitory and a microbicidal activity against all the tested strains. The spectrophotometric analysis showed that the treatment was effective in both reducing the previously developed biofilm and decreasing biofilm formation on titanium surfaces. Confocal laser scanning microscopy analysis showed a significant reduction of the total biofilm volume, with an increase of the percentage of dead cells of all the microorganisms tested.

CONCLUSIONS

Erythritol/chlorhexidine displayed significant antimicrobial and antibiofilm activity against microorganisms isolated from peri-implantitis lesions. Due to its properties, it might represent a promising approach for the prevention and treatment of peri-implant diseases associated to microbial biofilm infections.

Critical review on biofilm methods

Biofilms are widespread in nature and constitute an important strategy implemented by microorganisms to survive in sometimes harsh environmental conditions. They can be beneficial or have a negative impact particularly when formed in industrial settings or on medical devices. As such, research into the formation and elimination of biofilms is important for many disciplines. Several new methodologies have been recently developed for, or adapted to, biofilm studies that have contributed to deeper knowledge on biofilm physiology, structure and composition. In this review, traditional and cutting-edge methods to study biofilm biomass, viability, structure, composition and physiology are addressed. Moreover, as there is a lack of consensus among the diversity of techniques used to grow and study biofilms. This review intends to remedy this, by giving a critical perspective, highlighting the advantages and limitations of several methods. Accordingly, this review aims at helping scientists in finding the most appropriate and up-to-date methods to study their biofilms.

Assessing an imidazolium salt's performance as antifungal agent on a mouthwash formulation

AIMS

This study demonstrates the development of a mouthwash formulation containing the imidazolium salt (IMS) 1-n-hexadecyl-3-methylimidazolium chloride (C₁₆ MImCl), considering its stability and efficacy against Candida sp. Biofilm formation.

METHODS AND RESULTS

A variety of in vitro test methods were applied, assessing contaminated acrylic resin strip specimens before and after applying the mouthwash formulations. The formulation using C₁₆ MImCl presented a similar antibiofilm activity to cetylpyridinium chloride one and a commercial mouthwash, but at a 10 times lower concentration. Scanning electron microscopy imaging demonstrated that the selected mouthwash preparation fully destroys the biofilm cells, while with the hypoallergenicity test no irritant effect was observed in ex vivo model.

CONCLUSIONS

The results presented herein indicate a high potential for imidazolium salts application as mouthwash agents that can eliminate Candida biofilm growth at very low concentrations.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates a new and effective antibiofilm formulation containing the IMS C₁₆ MImCl. These findings suggest the IMS' use as mouthwash formulations active ingredient against Candida biofilms on oral surfaces, as it outperforms the often used cetylpyridinium chloride at a 10 times lower concentration.

Anti-biofilm and bactericidal effects of magnolia bark-derived magnolol and honokiol on Streptococcus mutans

Dental caries affects people of all ages and is a worldwide health concern. Streptococcus mutans is a major cariogenic bacterium because of its ability to form biofilm and induce an acidic environment. In this study, the antibacterial activities of magnolol and honokiol, the main constituents of the bark of magnolia plants, toward planktonic cell and biofilm of S. mutans were examined and compared with those of chlorhexidine. The minimal inhibitory concentrations of magnolol, honokiol and chlorhexidine for S. mutans were 10, 10 and 0.25 µg/mL, respectively. In addition, each agent showed bactericidal activity against S. mutans planktonic cells and inhibited biofilm formation in a dose- and time-dependent manner. Magnolol (50 µg/mL) had greater bactericidal activity against S. mutans biofilm than honokiol (50 µg/mL) and chlorhexidine (500 µg/mL) at 5 min after exposure, while all showed scant activity against biofilm at 30 s. Furthermore; chlorhexidine (0.5-500 µg/mL) exhibited high cellular toxicity for the gingival epithelial cell line Ca9-22 at 1 hr, whereas magnolol (50 µg/mL) and honokiol (50 µg/mL) did not. Thus; it was found that magnolol has antimicrobial activities against planktonic and biofilm cells of S. mutans. Magnolol may be a candidate for prevention and management of dental caries.

Vizantin inhibits bacterial adhesion without affecting bacterial growth and causes Streptococcus mutans biofilm to detach by altering its internal architecture

An ideal antibiofilm strategy is to control both in the quality and quantity of biofilm while maintaining the benefits derived from resident microflora. Vizantin, a recently developed immunostimulating compound, has also been found to have antibiofilm property. This study evaluated the influence on biofilm formation of Streptococcus mutans in the presence of sulfated vizantin and biofilm development following bacterial adhesion on a hydroxyapatite disc coated with sulfated vizantin. Supplementation with sulfated vizantin up to 50 μM did not affect either bacterial growth or biofilm formation, whereas 50 μM sulfated vizantin caused the biofilm to readily detach from the surface. Sulfated vizantin at the concentration of 50 μM upregulated the expression of the gtfB and gtfC genes, but downregulated the expression of the gtfD gene, suggesting altered architecture in the biofilm. Biofilm development on the surface coated with sulfated vizantin was inhibited depending on the concentration, suggesting prevention from bacterial adhesion. Among eight genes related to bacterial adherence in S. mutans, expression of gtfB and gtfC was significantly upregulated, whereas the expression of gtfD, GbpA and GbpC was downregulated according to the concentration of vizantin, especially with 50 μM vizantin by 0.8-, 0.4-, and 0.4-fold, respectively. These findings suggest that sulfated vizantin may cause structural degradation as a result of changing gene regulation related to bacterial adhesion and glucan production of S. mutans.

Chlorhexidine-induced elastic and adhesive changes of Escherichia coli cells within a biofilm

Chlorhexidine is a widely used, commercially available cationic antiseptic. Although its mechanism of action on planktonic bacteria has been well explored, far fewer studies have examined its interaction with an established biofilm. The physical effects of chlorhexidine on a biofilm are particularly unknown. Here, the authors report the first observations of chlorhexidine-induced elastic and adhesive changes to single cells within a biofilm. The elastic changes are consistent with the proposed mechanism of action of chlorhexidine. Atomic force microscopy and force spectroscopy techniques were used to determine spring constants and adhesion energy of the individual bacteria within an Escherichia coli biofilm. Medically relevant concentrations of chlorhexidine were tested, and cells exposed to 1% (w/v) and 0.1% more than doubled in stiffness, while those exposed to 0.01% showed no change in elasticity. Adhesion to the biofilm also increased with exposure to 1% chlorhexidine, but not for the lower concentrations tested. Given the prevalence of chlorhexidine in clinical and commercial applications, these results have important ramifications on biofilm removal techniques.

High-Velocity Microsprays Enhance Antimicrobial Activity in Streptococcus mutans Biofilms

Streptococcus mutans in dental plaque biofilms play a role in caries development. The biofilm's complex structure enhances the resistance to antimicrobial agents by limiting the transport of active agents inside the biofilm. The authors assessed the ability of high-velocity water microsprays to enhance delivery of antimicrobials into 3-d-old S. mutans biofilms. Biofilms were exposed to a 90° or 30° impact, first using a 1-µm tracer bead solution (10⁹ beads/mL) and, second, a 0.2% chlorhexidine (CHX) or 0.085% cetylpyridinium chloride (CPC) solution. For comparison, a 30-s diffusive transport and simulated mouthwash were also performed. Confocal microscopy was used to determine number and relative bead penetration depth into the biofilm. Assessment of antimicrobial penetration was determined by calculating the killing depth detected by live/dead viability staining. The authors first demonstrated that the microspray was able to deliver significantly more microbeads deeper in the biofilm compared with diffusion and mouthwashing exposures. Next, these experiments revealed that the microspray yielded better antimicrobial penetration evidenced by deeper killing inside the biofilm and a wider killing zone around the zone of clearance than diffusion alone. Interestingly the 30° impact in the distal position delivered approximately 16 times more microbeads and yielded approximately 20% more bacteria killing (for both CHX and CPC) than the 90° impact. These data suggest that high-velocity water microsprays can be used as an effective mechanism to deliver microparticles and antimicrobials inside S. mutans biofilms. High shear stresses generated at the biofilm-burst interface might have enhanced bead and antimicrobial delivery inside the remaining biofilm by combining forced advection into the biofilm matrix and physical restructuring of the biofilm itself. Further, the impact angle has potential to be optimized both for biofilm removal and active agents' delivery inside biofilm in those protected areas where some biofilm might remain.

Applying Adult Ventilator-associated Pneumonia Bundle Evidence to the Ventilated Neonate

BACKGROUND

Ventilator-associated pneumonia (VAP) in neonates can be reduced by implementing preventive care practices. Implementation of a group, or bundle, of evidence-based practices that improve processes of care has been shown to be cost-effective and to have better outcomes than implementation of individual single practices.

PURPOSE

The purpose of this article is to describe a safe, effective, and efficient neonatal VAP prevention protocol developed for caregivers in the neonatal intensive care unit (NICU). Improved understanding of VAP causes, effects of care practices, and rationale for interventions can help reduce VAP risk to neonatal patients.

METHOD

In order to improve care practices to affect VAP rates, initial and annual education occurred on improved protocol components after surveying staff practices and auditing documentation compliance.

FINDINGS/RESULTS

In 2009, a tertiary care level III NICU in the Midwestern United States had 14 VAP cases. Lacking evidence-based VAP prevention practices for neonates, effective adult strategies were modified to meet the complex needs of the ventilated neonate. A protocol was developed over time and resulted in an annual decrease in VAP until rates were zero for 20 consecutive months from October 2012 to May 2014.

IMPLICATIONS FOR PRACTICE

This article describes a VAP prevention protocol developed to address care practices surrounding hand hygiene, intubation, feeding, suctioning, positioning, oral care, and respiratory equipment in the NICU.

IMPLICATIONS FOR RESEARCH

Implementation of this VAP prevention protocol in other facilities with appropriate monitoring and tracking would provide broader support for standardization of care. Individual components of this VAP protocol could be studied to strengthen the inclusion of each; however, bundled interventions are often considered stronger when implemented as a whole.

In Vitro Activities of Nisin and Nisin Derivatives Alone and In Combination with Antibiotics against Staphylococcus Biofilms

The development and spread of pathogenic bacteria that are resistant to the existing catalog of antibiotics is a major public health threat. Biofilms are complex, sessile communities of bacteria embedded in an organic polymer matrix which serve to further enhance antimicrobial resistance. Consequently, novel compounds and innovative methods are urgently required to arrest the proliferation of drug-resistant infections in both nosocomial and community environments. Accordingly, it has been suggested that antimicrobial peptides could be used as novel natural inhibitors that can be used in formulations with synergistically acting antibiotics. Nisin is a member of the lantibiotic family of antimicrobial peptides that exhibit potent antibacterial activity against many Gram-positive bacteria. Recently we have used bioengineering strategies to enhance the activity of nisin against several high profile targets, including multi-drug resistant clinical pathogens such as methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, staphylococci, and streptococci associated with bovine mastitis. We have also identified nisin derivatives with an enhanced ability to impair biofilm formation and to reduce the density of established biofilms of methicillin resistant S. pseudintermedius. The present study was aimed at evaluating the potential of nisin and nisin derivatives to increase the efficacy of conventional antibiotics and to assess the possibility of killing and/or eradicating biofilm-associated cells of a variety of staphylococcal targets. Growth curve-based comparisons established that combinations of derivatives nisin V + penicillin or nisin I4V + chloramphenicol had an enhanced inhibitory effect against S. aureus SA113 and S. pseudintermedius DSM21284, respectively, compared to the equivalent nisin A + antibiotic combinations or when each antimicrobial was administered alone. Furthermore, the metabolic activity of established biofilms treated with nisin V + chloramphenicol and nisin I4V + chloramphenicol combinations revealed a significant decrease in S. aureus SA113 and S. pseudintermedius DSM21284 biofilm viability, respectively, compared to the nisin A + antibiotic combinations as determined by the rapid colorimetric XTT assay. The results indicate that the activities of the nisin derivative and antibiotic combinations represent a significant improvement over that of the wild-type nisin and antibiotic combination and merit further investigation with a view to their use as anti-biofilm agents.

Intermicrobial Interactions as a Driver for Community Composition and Stratification of Oral Biofilms

The oral cavity is accessible to microorganisms, and biofilms are present throughout on hard and soft tissues. The shedding of epithelial cell layers is usually effective for controlling biofilm development on soft tissues. Innate immune mechanisms are not so effective against biofilms on tooth surfaces, and oral hygiene measures such as brushing and flossing are required for the periodic removal of dental plaque. Even with good oral hygiene, microbial communities accumulate on teeth in areas that are protected from mechanical abrasion forces. Changes in the composition of these biofilms are associated with oral diseases such as dental caries or periodontitis. Newly formed biofilms and more mature dental plaque each have a level of spatial organization in the horizontal and vertical planes. Communities are shaped by many varied interactions between different species and genera within the biofilm, which include physical cell-cell associations known as coaggregation, interspecies signaling, secretion and turnover of antimicrobial compounds and the sharing of an extracellular matrix. Central to these interactions is the selection for metabolic synergies and it is becoming clear that the ability of communities to extract the maximum energy from the available metabolites is a potent driver for biofilm structure and stratification. This review discusses recent advances in our understanding of intermicrobial interactions in oral biofilms and the roles that they play in determining the spatial organization of biofilm communities.

Establishment of a multi-species biofilm model to evaluate chlorhexidine efficacy

BACKGROUND

Chronic infections, for example, diabetic foot ulcers, have a large impact in terms of patient morbidity and mortality. These wounds are characterized by complex polymicrobial communities of bacteria, which may include a number of difficult-to-eradicate multidrug-resistant pathogens.

AIM

To establish a multi-species biofilm model to test the efficacy of chlorhexidine and chlorhexidine-containing formulas in eradication of polymicrobial biofilms.

METHODS

A Centers for Disease Control and Prevention bioreactor was used to establish a multi-species biofilm incorporating Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus faecalis with equal numbers of each pathogen. This model was used to test the effectiveness of chlorhexidine at controlling the pre-formed biofilm.

FINDINGS

Chlorhexidine digluconate (CHD) was added to the bioreactor at a range of concentrations. K. pneumoniae and P. aeruginosa survived within multi-species biofilms, up to and including 4% CHD, whereas S. aureus was reduced to below the level of detection at 1%. Wiping the biofilm-containing coupons from the bioreactor with chlorhexidine-containing medical wipes resulted in >3 to <4log10 reduction after 24h, for all species. When the coupons were embedded in a simulated wound bed, formed in an agar plate, CHD-containing medical dressings completely eliminated S. aureus (>8log10 reduction), but had minimal effect (<3log10) against the other species tested.

CONCLUSION

The study demonstrates that the effectiveness of chlorhexidine may be limited in settings where it is required to act on multi-species biofilms. This may compromise the ability of chlorhexidine to control the infection and spread of these pathogens.

Ex vivo vs. in vivo antibacterial activity of two antiseptics on oral biofilm

Aim: To compare the immediate antibacterial effect of two application methods (passive immersion and active mouthwash) of two antiseptic solutions on the in situ oral biofilm.

Material and Methods: A randomized observer-masked crossover study was conducted. Fifteen healthy volunteers wore a specific intraoral device for 48 h to form a biofilm in three glass disks. One of these disks was used as a baseline; another one was immersed in a solution of 0.2% Chlorhexidine (0.2% CHX), remaining the third in the device, placed in the oral cavity, during the 0.2% CHX mouthwash application. After a 2-weeks washout period, the protocol was repeated using a solution of Essential Oils (EO). Samples were analyzed for bacterial viability with the confocal laser scanning microscope after previous staining with LIVE/DEAD® BacLight™.

Results: The EO showed a better antibacterial effect compared to the 0.2% CHX after the mouthwash application (% of bacterial viability = 1.16 ± 1.00% vs. 5.08 ± 5.79%, respectively), and was more effective in all layers (p < 0.05). In the immersion, both antiseptics were significantly less effective (% of bacterial viability = 26.93 ± 13.11%, EO vs. 15.17 ± 6.14%, 0.2% CHX); in the case of EO immersion, there were no significant changes in the bacterial viability of the deepest layer in comparison with the baseline.

Conclusions: The method of application conditioned the antibacterial activity of the 0.2% CHX and EO solutions on the in situ oral biofilm. The in vivo active mouthwash was more effective than the ex vivo passive immersion in both antiseptic solutions. There was more penetration of the antiseptic inside the biofilm with an active mouthwash, especially with the EO. Trial registered in clinicaltrials.gov with the number NCT02267239. URL: https://clinicaltrials.gov/ct2/show/NCT02267239.

Antimicrobial nisin acts against saliva derived multi-species biofilms without cytotoxicity to human oral cells

Objectives: Nisin is a lantibiotic widely used for the preservation of food and beverages. Recently, investigators have reported that nisin may have clinical applications for treating bacterial infections. The aim of this study was to investigate the effects of ultra pure food grade Nisin ZP (>95% purity) on taxonomically diverse bacteria common to the human oral cavity and saliva derived multi-species oral biofilms, and to discern the toxicity of nisin against human cells relevant to the oral cavity.

Methods: The minimum inhibitory concentrations and minimum bactericidal concentrations of taxonomically distinct oral bacteria were determined using agar and broth dilution methods. To assess the effects of nisin on biofilms, two model systems were utilized: a static and a controlled flow microfluidic system. Biofilms were inoculated with pooled human saliva and fed filter-sterilized saliva for 20–22 h at 37°C. Nisin effects on cellular apoptosis and proliferation were evaluated using acridine orange/ethidium bromide fluorescent nuclear staining and lactate dehydrogenase activity assays.

Results: Nisin inhibited planktonic growth of oral bacteria at low concentrations (2.5–50 μg/ml). Nisin also retarded development of multi-species biofilms at concentrations ≥1 μg/ml. Specifically, under biofilm model conditions, nisin interfered with biofilm development and reduced biofilm biomass and thickness in a dose-dependent manner. The treatment of pre-formed biofilms with nisin resulted in dose- and time-dependent disruption of the biofilm architecture along with decreased bacterial viability. Human cells relevant to the oral cavity were unaffected by the treatment of nisin at anti-biofilm concentrations and showed no signs of apoptotic changes unless treated with much higher concentrations (>200 μg/ml).

Conclusion: This work highlights the potential therapeutic value of high purity food grade nisin to inhibit the growth of oral bacteria and the development of biofilms relevant to oral diseases.

Antimicrobial Tolerance in Biofilms

The tolerance of microorganisms in biofilms to antimicrobial agents is examined through a meta-analysis of literature data. A numerical tolerance factor comparing the rates of killing in the planktonic and biofilm states is defined to provide a quantitative basis for the analysis. Tolerance factors for biocides and antibiotics range over three orders of magnitude. This variation is not explained by taking into account the molecular weight of the agent, the chemistry of the agent, the substratum material, or the speciation of the microorganisms. Tolerance factors do depend on the areal cell density of the biofilm at the time of treatment and on the age of the biofilm as grown in a particular experimental system. This suggests that there is something that happens during biofilm maturation, either physical or physiological, that is essential for full biofilm tolerance. Experimental measurements of antimicrobial penetration times in biofilms range over orders of magnitude, with slower penetration (>12 min) observed for reactive oxidants and cationic molecules. These agents are retarded through the interaction of reaction, sorption, and diffusion. The specific physiological status of microbial cells in a biofilm contributes to antimicrobial tolerance. A conceptual framework for categorizing physiological cell states is discussed in the context of antimicrobial susceptibility. It is likely that biofilms harbor cells in multiple states simultaneously (e.g., growing, stress-adapted, dormant, inactive) and that this physiological heterogeneity is an important factor in the tolerance of the biofilm state.

Silver nanoparticles with antimicrobial activities against Streptococcus mutans and their cytotoxic effect

Microbial resistance represents a challenge for the scientific community to develop new bioactive compounds. The goal of this research was to evaluate the antimicrobial activity of silver nanoparticles (AgNPs) against a clinical isolate of Streptococcus mutans, antibiofilm activity against mature S. mutans biofilms and the compatibility with human fibroblasts. The antimicrobial activity of AgNPs against the planktonic clinical isolate was size and concentration dependent, with smaller AgNPs having a lower minimum inhibitory concentration. A reduction of 2.3 log in the number of colony-forming units of S. mutans was observed when biofilms grown in a CDC reactor were exposed to 100 ppm of AgNPs of 9.5±1.1 nm. However, AgNPs at high concentrations (>10 ppm) showed a cytotoxic effect upon human dermal fibroblasts. AgNPs effectively inhibited the growth of a planktonic S. mutans clinical isolate and killed established S. mutans biofilms, which suggests that AgNPs could be used for prevention and treatment of dental caries. Further research and development are necessary to translate this technology into therapeutic and preventive strategies.

Sanitizing Effect of Ethanol Against Biofilms Formed by Three Gram-Negative Pathogenic Bacteria

Sanitizing effect of ethanol on a Yersinia enterocolitica biofilm was evaluated in terms of biomass removal and bactericidal activity. We found that 40 % ethanol was most effective for biofilm biomass removal; however, no significant difference was observed in bactericidal activity between treatment with 40 and 70 % ethanol. This unexpected low ethanol concentration requirement for biomass removal was confirmed using biofilms of two additional pathogenic bacteria, Aeromonas hydrophila and Xanthomonas oryzae. Although only three pathogenic Gram-negative bacteria were tested and the biofilm in nature was different from the biofilm in this study, the results in this study suggested the possible re-evaluation of the effective sanitizing ethanol concentration 70 %, which is the concentration commonly employed for sanitization, on bacteria in a biofilm.