A Sustained-Release Membrane of Thiazolidinedione-8: Effect on Formation of a Candida/Bacteria Mixed Biofilm on Hydroxyapatite in a Continuous Flow Model

Thiazolidin-4-Ones as a Promising Scaffold in the Development of Antibiofilm Agents-A Review

Thiazolidin-4-ones have a broad range of medical and clinical implementation, which is important for pharmaceutical and medicinal chemistry. This heterocyclic core has been reported to possess a diversity of bioactivities, including antimicrobial and antibiofilm-forming potential. The resistance of biofilms to antibiotics or disinfectants is a serious medical problem. Therefore, there is a natural need to discover new effective structures with properties that inhibit biofilm formation. This review aims to analyze the antibiofilm features of thiazolidin-4-ones described in the literature over the last two decades. The information gathered in this review could benefit the rational design of new effective antibiofilm small molecules with thiazolidin-4-one cores.

Supra and subgingival application of antiseptics or antibiotics during periodontal therapy

Periodontal diseases (gingivitis and periodontitis) are characterized by inflammatory processes which arise as a result of disruption of the balance in the oral ecosystem. According to the current S3 level clinical practice guidelines, therapy of patients with periodontitis involves a stepwise approach that includes the control of the patient's risk factors and the debridement of supra and subgingival biofilm. This debridement can be performed with or without the use of some adjuvant therapies, including physical or chemical agents, host modulating agents, subgingivally locally delivered antimicrobials, or systemic antimicrobials. Therefore, the main aim of this article is to review in a narrative manner the existing literature regarding the adjuvant application of local agents, either subgingivally delivered antibiotics and antiseptics or supragingivally applied rinses and dentifrices, during the different steps in periodontal therapy performed in Europe.

Prolonged Inhibition of Streptococcus mutans Growth and Biofilm Formation by Sustained Release of Chlorhexidine from Varnish Coated Dental Abutments: An in Vitro Study

Background

It has been confirmed that bacterial biofilm covering dental implants is the main microbial source causing preimplant infectious and inflammatory diseases. The purpose of this study was to evaluate the antibacterial/antibiofilm effect of chlorhexidine, incorporated into a sustained-release varnish of chlorhexidine (SRV-CHX) coating, on dental abutments.

Materials and Methods

Three kinds of dental abutments were used: a high-performance semi-crystalline engineering thermoplastic polyetheretherketone (PEAK) healing abutment, a titanium healing abutment, and a titanium permanent abutment. These abutments were coated with SRV-CHX or SRV-placebo and exposed daily to fresh cultures of Streptococcus mutans. The effect of SRV-CHX on S. mutans growth on agar plates was studied by measuring the zone of inhibition (ZOI) around each tested abutment every day for a period of 36 days. Biofilm formation on the SRV-CHX/placebo-coated abutments was detected using confocal laser scanning microscopy (CLSM) and high-resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX), and monitored by crystal violet (CV) staining.

Results

SRV-CHX-coated abutments 2 and 3 were able to inhibit S. mutans growth for 34 days, while abutment 1 inhibited growth for 32 days. Abutment-associated biofilm formation was notably inhibited by SRV-CHX coating after 13 days of incubation with S. mutans. Finally, the biofilm formed around SRV-CHX-coated abutments was completely inhibited up to 12 days of abutment exposure to S. mutans.

Conclusion

Coating of dental abutments with SRV-CHX demonstrated long-term effective inhibition of S. mutans growth and biofilm formation on the abutment surface.

Quorum Sensing and Quorum Quenching with a Focus on Cariogenic and Periodontopathic Oral Biofilms

Numerous in vitro studies highlight the role of quorum sensing in the pathogenicity and virulence of biofilms. This narrative review discusses general principles in quorum sensing, including Gram-positive and Gram-negative models and the influence of flow, before focusing on quorum sensing and quorum quenching in cariogenic and periodontopathic biofilms. In cariology, quorum sensing centres on the role of Streptococcus mutans, and to a lesser extent Candida albicans, while Fusobacterium nucleatum and the red complex pathogens form the basis of the majority of the quorum sensing research on periodontopathic biofilms. Recent research highlights developments in quorum quenching, also known as quorum sensing inhibition, as a potential antimicrobial tool to attenuate the pathogenicity of oral biofilms by the inhibition of bacterial signalling networks. Quorum quenchers may be synthetic or derived from plant or bacterial products, or human saliva. Furthermore, biofilm inhibition by coating quorum sensing inhibitors on dental implant surfaces provides another potential application of quorum quenching technologies in dentistry. While the body of predominantly in vitro research presented here is steadily growing, the clinical value of quorum sensing inhibitors against in vivo oral polymicrobial biofilms needs to be ascertained.

Potential Combinatory Effect of Cannabidiol and Triclosan Incorporated into Sustained Release Delivery System against Oral Candidiasis

Candida albicans is a common fungal pathogen. Biofilm formation on various surfaces is an important determinant of C. albicans pathogenicity. Our previous results demonstrated the high potential of cannabidiol (CBD) to affect C. albicans biofilms. Based on these data, we investigated the possibility of incorporating CBD and/or triclosan (an antimicrobial agent that is widely utilized in dentistry) in a sustained-release varnish (SRV) (SRV-CBD, SRV-triclosan) to increase their pharmaceutical potential against C. albicans biofilm, as well as that of the mixture of the agents into SRV (SRV-CBD/triclosan). The study was conducted in a plastic model, on agar, and in an ex vivo tooth model. Our results demonstrated strong antibiofilm activity of SRV-CBD and SRV-triclosan against C. albicans in all tested models. Both formulations were able to inhibit biofilm formation and to remove mature fungal biofilm. In addition, SRV-CBD and SRV-triclosan altered C. albicans morphology. Finally, we observed a dramatic enhancement of antibiofilm activity when combined SRV-CBD/triclosan was applied. In conclusion, we propose that incorporation of CBD or triclosan into SRV is an effective strategy to fight fungal biofilms. Importantly, the data demonstrate that our CBD/triclosan varnish is safe, and is not cytotoxic for normal mammalian cells. Furthermore, we propose that CBD and triclosan being in mixture in SRV exhibit complementary antibiofilm activity, and thus can be explored for further development as a potential treatment against fungal infections.

Recent Advances and Opportunities in the Study of Candida albicans Polymicrobial Biofilms

It is well known that the opportunistic pathogenic yeast, Candida albicans, can form polymicrobial biofilms with a variety of bacteria, both in vitro and in vivo, and that these polymicrobial biofilms can impact the course and management of disease. Although specific interactions are often described as either synergistic or antagonistic, this may be an oversimplification. Polymicrobial biofilms are complex two-way interacting communities, regulated by inter-domain (inter-kingdom) signaling and various molecular mechanisms. This review article will highlight advances over the last six years (2016-2021) regarding the unique biology of polymicrobial biofilms formed by C. albicans and bacteria, including regulation of their formation. In addition, some of the consequences of these interactions, such as the influence of co-existence on antimicrobial susceptibility and virulence, will be discussed. Since the aim of this knowledge is to inform possible alternative treatment options, recent studies on the discovery of novel anti-biofilm compounds will also be included. Throughout, an attempt will be made to identify ongoing challenges in this area.

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.

Sinonasal Stent Coated with Slow-Release Varnish of Chlorhexidine Has Sustained Protection against Bacterial Biofilm Growth in the Sinonasal Cavity: An In Vitro Study

The aim of the study was to develop a sustained-release varnish (SRV) containing chlorhexidine (CHX) for sinonasal stents (SNS) to reduce bacterial growth and biofilm formation in the sinonasal cavity. Segments of SNS were coated with SRV-CHX or SRV-placebo and exposed daily to bacterial cultures of Staphylococcus aureus subsp. aureus ATCC 25923 or Pseudomonas aeruginosa ATCC HER-1018 (PAO1). Anti-bacterial effects were assessed by disc diffusion assay and planktonic-based activity assay. Biofilm formation on the coated stents was visualized by confocal laser scanning microscopy (CLSM) and high-resolution scanning electron microscopy (HR-SEM). The metabolic activity of the biofilms was determined using the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) method. Disc diffusion assay showed that SRV-CHX-coated SNS segments inhibited bacterial growth of S. aureussubsp. aureus ATCC 25923 for 26 days and P. aeruginosa ATCC HER-1018 for 19 days. CHX was released from coated SNS segments in a pH 6 medium up to 30 days, resulting in growth inhibition of S. aureussubsp. aureus ATCC 25923 for 22 days and P. aeruginosa ATCC HER-1018 for 24 days. The MTT assay showed a reduction of biofilm growth on the coated SNS by 69% for S. aureussubsp. aureus ATCC 25923 and 40% for P. aeruginosa ATCC HER-1018 compared to the placebo stent after repeated exposure to planktonic growing bacteria. CLSM and HR-SEM showed a significant reduction of biofilm formation on the SRV-CHX-coated SNS segments. Coating of SNS with SRV-CHX maintains a sustained delivery of CHX, providing an inhibitory effect on the bacterial growth of S. aureussubsp. aureus ATCC 25923 and P. aeruginosa ATCC HER-1018 for approximately 3 weeks.

Efficiency of Bacillus subtilis metabolism of sugar alcohols governs its probiotic effect against cariogenic Streptococcus mutans

Bacillus subtilis is a Gram-positive probiotic bacterium that successfully colonises plant roots due to its ability to utilise various sugars. The vast probiotic potential of B. subtilis has been recently demonstrated in numerous host organisms under different environmental conditions. We examined the probiotic potential of B. subtilis against the pathogenic bacterium Streptococcus mutans, which is involved in various oral disorders due to its robust biofilm-forming capability. B. subtilis cells attenuated biofilm formation by S. mutans during their dual growth in the presence of sugar alcohols. Transcription of genes encoding key enzymes in the metabolism of sugar alcohols by B. subtilis were highly induced. Moreover, growth-curve analysis suggested that B. subtilis is more efficient at early utilising sugar alcohols than S. mutans, as supported by the bacterial metabolic activity rates. Similarly, a comparison of secondary metabolites of mono and mixed cultures of B. subtilis and S. mutans indicated that B. subtilis is more active metabolically in the dual culture. Finally, knock-out mutations of the genes encoding key enzymes in the central metabolic pathway significantly reduced B. subtilis' ability to mitigate biofilm formation by S. mutans. We conclude that effective metabolism of sugar alcohols by B. subtilis reinforces the probiotic potential of this bacterium against pathogenic species such as S. mutans.

Mixed biofilms of pathogenic Candida-bacteria: regulation mechanisms and treatment strategies

Mixed-species biofilm is one of the most frequently recorded clinical problems. Mixed biofilms develop as a result of interactions between microorganisms of a single or multiple species (e.g. bacteria and fungi). Candida spp., particularly Candida albicans, are known to associate with various bacterial species to form a multi-species biofilm. Mixed biofilms of Candida spp. have been previously detected in vivo and on the surfaces of many biomedical instruments. Treating infectious diseases caused by mixed biofilms of Candida and bacterial species has been challenging due to their increased resistance to antimicrobial drugs. Here, we review and discuss the clinical significance of mixed Candida-bacteria biofilms as well as the signalling mechanisms involved in Candida-bacteria interactions. We also describe possible approaches for combating infections associated with mixed biofilms, such as the use of natural or synthetic drugs and combination therapy. The review presented here is expected to contribute to the advances in the biomedical field on the understanding of underlying interaction mechanisms of pathogens in mixed biofilm, and alternative approaches to treating the related infections.

Mechanisms of Candida Resistance to Antimycotics and Promising Ways to Overcome It: The Role of Probiotics

Pathogenic Candida and infections caused by those species are now considered as a serious threat to public health. The treatment of candidiasis is significantly complicated by the increasing resistance of pathogenic strains to current treatments and the stagnant development of new antimycotic drugs. Many species, such as Candida auris, have a wide range of resistance mechanisms. Among the currently used synthetic and semi-synthetic antifungal drugs, the most effective are azoles, echinocandins, polyenes, nucleotide analogs, and their combinations. However, the use of probiotic microorganisms and/or the compounds they produce is quite promising, although underestimated by modern pharmacology, to control the spread of pathogenic Candida species.

Microbial Interkingdom Biofilms and the Quest for Novel Therapeutic Strategies

Fungal and bacterial species interact with each other within polymicrobial biofilm communities in various niches of the human body. Interactions between these species can greatly affect human health and disease. Diseases caused by polymicrobial biofilms pose a major challenge in clinical settings because of their enhanced virulence and increased drug tolerance. Therefore, different approaches are being explored to treat fungal-bacterial biofilm infections. This review focuses on the main mechanisms involved in polymicrobial drug tolerance and the implications of the polymicrobial nature for the therapeutic treatment by highlighting clinically relevant fungal-bacterial interactions. Furthermore, innovative treatment strategies which specifically target polymicrobial biofilms are discussed.

Biofilm distribution on tympanostomy tubes: An ex vivo descriptive study

BACKGROUND

Tympanostomy tube (TT) insertion is a common procedure in children with otitis media with effusion. Post-TT otorrhea (PTTO) is a frequent post-operative complication. Biofilms are involved in chronic PTTO cases.

OBJECTIVE

To describe and qualitatively analyze the geometry and sites prone to biofilms on removed TTs, relatively to their position in the ear, past medical/surgical history and PTTO presence.

METHODS

Biofilms presence and topographic distribution on TTs were ex vivo evaluated by using scanning electron microscope, confocal microscope and stereo-microscope.

RESULTS

Forty-eight TTs from 30 children were analyzed. Indications for removal were: 71% due to retained TTs (average time from insertion: 24.4 ± 15.1 months), 23% due to chronic PTTO, and 6% due to TT obstruction/dysfunction. Different types of bacterial biofilms were detected on all TTs, regardless the time from their insertion nor their types. Biofilms were observed more on the perpendicular junction and on the internal lumen, and more biofilm colonies were detected on the medial part, facing the middle ear mucosa. TTs removed from children with PTTO exhibited more biofilm colonies when compared to their peers. Of the 16 children who underwent adenoidectomy concomitantly with TT insertion, 10 (62%) children were sent for TT removal due to retained TTs, and 6 (38%) children due to chronic PTTO (p = 0.03).

CONCLUSION

Descriptive analysis of biofilm topographic distribution demonstrated adhesions on specific TT areas: perpendicular junctions and the internal lumen. Such "prone zones" may be the future target areas for changes in TT geometry or can be specifically coated with anti-biofilm materials.

Sustained-release delivery of antimicrobial drugs for the treatment of periodontal diseases: Fantasy or already reality?

Periodontal diseases are prevalent in humans. Conventional means of combating these diseases involve basic oral hygiene, mostly toothbrushing, use of mouthwashes, and flossing. Supplementary means of treatment, either clinical or pharmaceutical, are often necessary. The use of sustained-release delivery systems, applied locally to the periodontal pocket, seems to be one feasible approach: local sustained-release delivery of antibacterial agents to treat periodontal diseases is conceivable. The use of local (intrapocket) sustained-release delivery systems has numerous clinical, pharmacologic, and toxicologic advantages over conventional treatments for periodontal diseases. Sustained-release technology has been proven to be effective over the last few decades. Films, gels, and fibers are the three main classical intrapocket pharmaceutical delivery systems. Research today is more focused on improving drug delivery, and less on introducing new drugs. New approaches, eg, those making use of nanotechnology, are emerging for local drug-delivery systems. The local sustained-release delivery system concept is innovative and a few products are already commercially available.

Management of Streptococcus mutans-Candida spp. Oral Biofilms' Infections: Paving the Way for Effective Clinical Interventions

Oral diseases are considered the most common noncommunicable diseases and are related to serious local and systemic disorders. Oral pathogens can grow and spread in the oral mucosae and frequently in biomaterials (e.g., dentures or prostheses) under polymicrobial biofilms, leading to several disorders such as dental caries and periodontal disease. Biofilms harbor a complex array of interacting microbes, increasingly unapproachable to antimicrobials and with dynamic processes key to disease pathogenicity, which partially explain the gradual loss of response towards conventional therapeutic regimens. New drugs (synthesized and natural) and other therapies that have revealed promising results for the treatment or control of these mixed biofilms are presented and discussed here. A structured search of bibliographic databases was applied to include recent research. There are several promising new approaches in the treatment of Candida spp.-Streptococcus mutans oral mixed biofilms that could be clinically applied in the near future. These findings confirm the importance of developing effective therapies for oral Candida-bacterial infections.

Proteolytic Activity of Bacillus subtilis upon κ-Casein Undermines Its "Caries-Safe" Effect

Milk is believed to be a relatively “caries-safe” food. This belief relies on the fact that caseins, which constitute around 80% of milk’s protein content, were found to inhibit the adhesion of Streptococcus mutans to enamel and, therefore, decrease biofilm formation. While S. mutans is considered a leading cause of dental disorders, Bacillus subtilis is a non-pathogenic foodborne bacterium, frequently contaminating milk and its products. This study aimed to investigate the effects of dairy-associated foodborne bacteria such as B. subtilis on biofilm formation by S. mutans in the presence of casein proteins. Our results indicate that there is a significant decrease in total biofilm formation by S. mutans exposed to a casein protein mixture in a mono-species culture, whereas, in the co-culture with B. subtilis, an inhibitory effect of the caseins mixture on S. mutans biofilm formation was observed. Proteolytic activity analysis suggested that B. subtilis is capable of breaking down milk proteins, especially κ-casein, which enables biofilm formation by S. mutans in the presence of milk caseins. Therefore, these findings may challenge the assumption that milk is “caries-safe”, especially in a complex microbial environment.

Candida spp./Bacteria Mixed Biofilms

The ability to form biofilms is a common feature of microorganisms, such as bacteria or fungi. These consortiums can colonize a variety of surfaces, such as host tissues, dentures, and catheters, resulting in infections highly resistant to drugs, when compared with their planktonic counterparts. This refractory effect is particularly critical in polymicrobial biofilms involving both fungi and bacteria. This review emphasizes Candida spp.-bacteria biofilms, the epidemiology of this community, the challenges in the eradication of such biofilms, and the most relevant treatments.

Design, Synthesis and Biological Evaluation of New Piperazin-4-yl-(acetyl-thiazolidine-2,4-dione) Norfloxacin Analogues as Antimicrobial Agents

In an effort to improve the antimicrobial activity of norfloxacin, a series of hybrid norfloxacin–thiazolidinedione molecules were synthesized and screened for their direct antimicrobial activity and their anti-biofilm properties. The new hybrids were intended to have a new binding mode to DNA gyrase, that will allow for a more potent antibacterial effect, and for activity against current quinolone-resistant bacterial strains. Moreover, the thiazolidinedione moiety aimed to include additional anti-pathogenicity by preventing biofilm formation. The resulting compounds showed promising direct activity against Gram-negative strains, and anti-biofilm activity against Gram-positive strains. Docking studies and ADMET were also used in order to explain the biological properties and revealed some potential advantages over the parent molecule norfloxacin.

Influence of Thiazolidine-2,4-Dione Derivatives with Azolidine or Thiosemicarbazone Moieties on Haemophilus spp. Planktonic or Biofilm-Forming Cells

Biofilm, naturally formed by microorganisms as integrated surface-bound communities, is one of the reasons for the development of antimicrobial resistance. Haemophilus spp. are common and representative opportunistic Gram-negative rods forming from the upper respiratory tract microbiota. The aim of this paper was to evaluate the influence of thiazolidine-2,4-dionebased azolidine and chlorophenylthiosemicarbazone hybrids against both planktonic and biofilm-forming Haemophilus spp. cells. The in vitro activity against planktonic and biofilm-forming cells of the tested compounds were evaluated by using the broth microdilution method. These activities were detected against reference and clinical strains of Haemophilus spp. on the basis of MICs (minimal inhibitory concentrations) and MBICs (minimal biofilm inhibitory concentrations). In addition, anti-adhesive properties of these compounds were examined. The target compounds showed potential activity against planktonic cells with MIC = 62.5–500 mg/L and biofilm-forming cells with MBIC = 62.5–1000 mg/L. The observed anti-adhesive properties of the tested compounds were reversible during long-term incubation in a lower concentration of compounds.

Adaptation of Bacillus species to dairy associated environment facilitates their biofilm forming ability

Biofilm-forming Bacillus species are often involved in contamination of dairy products and therefore present a major microbiological challenge in the field of food quality and safety. In this study, we sequenced and analyzed the genomes of milk- and non-milk-derived Bacillus strains, and evaluated their biofilm-formation potential in milk. Unlike non-dairy Bacillus isolates, the dairy-associated Bacillus strains were characterized by formation of robust submerged and air-liquid interface biofilm (pellicle) during growth in milk. Moreover, genome comparison analysis revealed notable differences in putative biofilm-associated determinants between the dairy and non-dairy Bacillus isolates, which correlated with biofilm phenotype. These results suggest that biofilm formation by Bacillus species might represent a presumable adaptation strategy to the dairy environment.

Antimicrobial potential of endocannabinoid and endocannabinoid-like compounds against methicillin-resistant Staphylococcus aureus

Infections caused by antibiotic-resistant strains of Staphylococcus aureus have reached epidemic proportions globally. Staphylococcal biofilms are associated with increased antimicrobial resistance and are generally less affected by host immune factors. Therefore, there is an urgent need for novel agents that not only aim at multidrug-resistant pathogens, but also ones that will act as anti biofilms. In the present study, we investigated the antimicrobial activity of the endocannabinoid (EC) anandamide (AEA) and the endocannabinoid-like (EC-like), arachidonoyl serine (AraS) against methicillin resistant S. aureus strains (MRSA). We observed a strong inhibition of biofilm formation of all tested MRSA strains as well as a notable reduction of metabolic activity of pre-formed MRSA biofilms by both agents. Moreover, staphylococcal biofilm-associated virulence determinants such as hydrophobicity, cell aggregation and spreading ability were altered by AEA and AraS. In addition, the agents were able to modify bacterial membrane potential. Importantly, both compounds prevent biofilm formation by altering the surface of the cell without killing the bacteria. Therefore, we propose that EC and EC-like compounds may act as a natural line of defence against MRSA or other antibiotic resistant bacteria. Due to their anti biofilm action these agents could also be a promising alternative to antibiotic therapeutics against biofilm-associated MRSA infections.

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.