An In Vitro Model for Oral Mixed Biofilms of Candida albicans and Streptococcus gordonii in Synthetic Saliva

Construction of a versatile in vitro cultivation screening platform using human oral microbiota

We developed a simulation model of human oral microbiota using Bio Palette oral medium (BPOM) containing 0.02% glucose and lower bacterial nitrogen sources, derived from saliva and dental plaque. By decreasing the concentration of Gifu anaerobic medium (GAM) from 30 to 10 g L-1 , we observed increased ratios of target pathogenic genera, Porphyromonas and Fusobacterium from 0.5% and 1.7% to 1.2% and 3.5%, respectively, in the biofilm on hydroxyapatite (HA) discs. BPOM exhibited the higher ratios of Porphyromonas and Fusobacterium, and amplicon sequence variant number on HA, compared with GAM, modified GAM and basal medium mucin. Mixing glycerol stocks of BPOM culture solutions from four human subjects resulted in comparable ratios of these bacteria to the original saliva. In this simulation model, sitafloxacin showed higher inhibitory effects on P. gingivalis than minocycline hydrochloride at a low dosage of 0.1 μg mL-1 . Probiotics such as Streptococcus salivarius and Limosilactobacillus fermentum also showed significant decreases in Porphyromonas and Fusobacterium ratios on HA, respectively. Overall, the study suggests that BPOM with low carbon and nutrients could be a versatile platform for assessing the efficacy of antibiotics and live biotherapeutics in treating oral diseases caused by Porphyromonas and Fusobacterium.

Investigating the role of Candida albicans as a universal substrate for oral bacteria using a transcriptomic approach: implications for interkingdom biofilm control?

Candida albicans is frequently identified as a colonizer of the oral cavity in health and has recently been termed a "keystone" commensal due to its role on the bacterial communities. However, the role that C. albicans plays in such interactions is not fully understood. Therefore, this study aimed to identify the relationship between C. albicans and bacteria associated with oral symbiosis and dysbiosis. To do this, we evaluated the ability of C. albicans to support the growth of the aerobic commensal Streptococcus gordonii and the anaerobic pathogens Fusobacterium nucleatum and Porphyromonas gingivalis in the biofilm environment. RNA-Sequencing with the Illumina platform was then utilized to identify C. albicans gene expression and functional pathways involved during such interactions in dual-species and a 4-species biofilm model. Results indicated that C. albicans was capable of supporting growth of all three bacteria, with a significant increase in colony counts of each bacteria in the dual-species biofilm (p < 0.05). We identified specific functional enrichment of pathways in our 4-species community as well as transcriptional profiles unique to the F. nucleatum and S. gordonii dual-species biofilms, indicating a species-specific effect on C. albicans. Candida-related hemin acquisition and heat shock protein mediated processes were unique to the organism following co-culture with anaerobic and aerobic bacteria, respectively, suggestive that such pathways may be feasible options for therapeutic targeting to interfere with these fungal-bacterial interactions. Targeted antifungal therapy may be considered as an option for biofilm destabilization and treatment of complex communities. Moving forward, we propose that further studies must continue to investigate the role of this fungal organism in the context of the interkingdom nature of oral diseases.

Development of in vitro methods to model the impact of vaginal lactobacilli on Staphylococcus aureus biofilm formation on menstrual cups as well as validation of recommended cleaning directions

Introduction

Menstrual cups (MC) are a reusable feminine hygiene product. A recent publication suggested that Staphylococcus aureus (S. aureus) biofilms can form on MCs which may lead to increased risk of menstrual Toxic Shock Syndrome (mTSS). Additionally, there is concern that buildup of residual menses may contribute to microbial growth and biofilm formation further increasing mTSS risk. Quantitative and qualitative analysis of in vitro tests were utilized to determine if S. aureus biofilm could form on MC in the presence of the keystone species Lactobacillus after 12 h of incubation. The methodology was based on a modification of an anaerobic in vitro method that harnesses the keystone species hypothesis by including a representative of vaginal lactic acid bacteria.

Methods

MCs were incubated anaerobically for 12 h in Vaginal Defined Media (VDM) with the two morphologically distinct bacteria, Lactobacillus gasseri (L. gasseri) and S. aureus. Colony Forming Units (CFU) for each organism from the VDM broth and sonicated MC were estimated. In addition, a separate experiment was conducted where S. aureus was grown for 12 h in the absence of L. gasseri. Qualitative analysis for biofilm formation utilized micro-CT (µ-CT) and cryogenic scanning electron microscopy (Cryo-SEM).

Results

Samples collected from the media control had expected growth of both organisms after 12 h of incubation. Samples collected from VDM broth were similar to media control at the end of the 12-h study. Total S. aureus cell density on MC following sonication/rinsing was minimal. Results when using a monoculture of S. aureus demonstrated that there was a significant growth of the organism in the media control and broth as well as the sonicated cups indicating that the presence of L. gasseri was important for controlling growth and adherence of S. aureus. Few rod-shaped bacteria (L. gasseri) and cocci (S. aureus) could be identified on the MCs when grown in a dual species culture inoculum and no biofilm was noted via µ-CT and cryo-SEM. Additionally, efforts to model and understand the validity of the current labeled recommendations for MC cleaning in-between uses are supported.

Discussion

The data support continued safe use of the Tampax® cup when used and maintained as recommended.

Living together: The role of Candida albicans in the formation of polymicrobial biofilms in the oral cavity

The oral cavity of humans is colonized by diversity of microbial community, although dominated by bacteria, it is also constituted by a low number of fungi, often represented by Candida albicans. Although in the vast minority, this usually commensal fungus under certain conditions of the host (e.g., immunosuppression or antibiotic therapy), can transform into an invasive pathogen that adheres to mucous membranes and also to medical or dental devices, causing mucosal infections. This transformation is correlated with changes in cell morphology from yeast-like cells to hyphae and is supported by numerous virulence factors exposed by C. albicans cells at the site of infection, such as multifunctional adhesins, degradative enzymes, or toxin. All of them affect the surrounding host cells or proteins, leading to their destruction. However, at the site of infection, C. albicans can interact with different bacterial species and in its filamentous form may produce biofilms-the elaborated consortia of microorganisms, that present increased ability to host colonization and resistance to antimicrobial agents. In this review, we highlight the modification of the infectious potential of C. albicans in contact with different bacterial species, and also consider the mutual bacterial-fungal relationships, involving cooperation, competition, or antagonism, that lead to an increase in the propagation of oral infection. The mycofilm of C. albicans is an excellent hiding place for bacteria, especially those that prefer low oxygen availability, where microbial cells during mutual co-existence can avoid host recognition or elimination by antimicrobial action. However, these microbial relationships, identified mainly in in vitro studies, are modified depending on the complexity of host conditions and microbial dominance in vivo.

The interactions of Candida albicans with gut bacteria: a new strategy to prevent and treat invasive intestinal candidiasis

BACKGROUND

The gut microbiota plays an important role in human health, as it can affect host immunity and susceptibility to infectious diseases. Invasive intestinal candidiasis is strongly associated with gut microbiota homeostasis. However, the nature of the interaction between Candida albicans and gut bacteria remains unclear.

OBJECTIVE

This review aimed to determine the nature of interaction and the effects of gut bacteria on C. albicans so as to comprehend an approach to reducing intestinal invasive infection by C. albicans.

METHODS

This review examined 11 common gut bacteria's interactions with C. albicans, including Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii, Enterococcus faecalis, Staphylococcus aureus, Salmonella spp., Helicobacter pylori, Lactobacillus spp., Bacteroides spp., Clostridium difficile, and Streptococcus spp.

RESULTS

Most of the studied bacteria demonstrated both synergistic and antagonistic effects with C. albicans, and just a few bacteria such as P. aeruginosa, Salmonella spp., and Lactobacillus spp. demonstrated only antagonism against C. albicans.

CONCLUSIONS

Based on the nature of interactions reported so far by the literature between gut bacteria and C. albicans, it is expected to provide new ideas for the prevention and treatment of invasive intestinal candidiasis.

Impact of the host microbiota on fungal infections: new possibilities for intervention?

Many human fungal pathogens are opportunistic. They are primarily benign residents of the human body and only become infectious when the host's immunity and microbiome are compromised. Bacteria dominate the human microbiome, playing an essential role in keeping fungi harmless and acting as the first line of defense against fungal infection. The Human Microbiome Project, launched by NIH in 2007, has stimulated extensive investigation and significantly advanced our understanding of the molecular mechanisms governing the interaction between bacteria and fungi, providing valuable insights for developing future antifungal strategies by exploiting the interaction. This review summarizes recent progress in this field and discusses new possibilities and challenges. We must seize the opportunities presented by researching bacterial-fungal interplay in the human microbiome to address the global spread of drug-resistant fungal pathogens and the drying pipelines of effective antifungal drugs.

Generation of Multispecies Oral Bacteria Biofilm Models

It is well-recognized that oral biofilms that occur in health and disease have a polymicrobial composition, though these are poorly reflected in the literature, with many studies focussing on simple mono-species biofilm model systems. The utility of polymicrobial biofilm model systems is that they more accurately reflect the oral cavity and allow researchers to ask relevant questions in basic science studies, pharmaceutical screening, and investigating inflammatory interactions. Here we describe the detailed methodology of how to sequentially construct and maintain polymicrobial biofilm models pertinent to caries, periodontal disease, and denture stomatitis.

Cross-kingdom interaction between Candida albicans and oral bacteria

Candida albicans is a symbiotic fungus that commonly colonizes on oral mucosal surfaces and mainly affects immuno-compromised individuals. Polymicrobial interactions between C. albicans and oral microbes influence the cellular and biochemical composition of the biofilm, contributing to change clinically relevant outcomes of biofilm-related oral diseases, such as pathogenesis, virulence, and drug-resistance. Notably, the symbiotic relationships between C. albicans and oral bacteria have been well-documented in dental caries, oral mucositis, endodontic and periodontal diseases, implant-related infections, and oral cancer. C. albicans interacts with co-existing oral bacteria through physical attachment, extracellular signals, and metabolic cross-feeding. This review discusses the bacterial-fungal interactions between C. albicans and different oral bacteria, with a particular focus on the underlying mechanism and its relevance to the development and clinical management of oral diseases.

Access to Anti-Biofilm Compounds from Endolichenic Fungi Using a Bioguided Networking Screening

Endolichenic microorganisms represent a new source of bioactive natural compounds. Lichens, resulting from a symbiotic association between algae or cyanobacteria and fungi, constitute an original ecological niche for these microorganisms. Endolichenic fungi inhabiting inside the lichen thallus have been isolated and characterized. By cultivation on three different culture media, endolichenic fungi gave rise to a wide diversity of bioactive metabolites. A total of 38 extracts were screened for their anti-maturation effect on Candida albicans biofilms. The 10 most active ones, inducing at least 50% inhibition, were tested against 24 h preformed biofilms of C. albicans, using a reference strain and clinical isolates. The global molecular network was associated to bioactivity data in order to identify and priorize active natural product families. The MS-targeted isolation led to the identification of new oxygenated fatty acid in Preussia persica endowed with an interesting anti-biofilm activity against C. albicans yeasts.

Interactions between Candida albicans and the resident microbiota

Candida albicans is a prevalent, opportunistic human fungal pathogen. It usually dwells in the human body as a commensal, however, once in its pathogenic state, it causes diseases ranging from debilitating superficial to life-threatening systemic infections. The switch from harmless colonizer to virulent pathogen is, in most cases, due to perturbation of the fungus-host-microbiota interplay. In this review, we focused on the interactions between C. albicans and the host microbiota in the mouth, gut, blood, and vagina. We also highlighted important future research directions. We expect that the evaluation of these interplays will help better our understanding of the etiology of fungal infections and shed new light on the therapeutic approaches.

Biofilm Formation by Chromoblastomycosis Fungi Fonsecaea pedrosoi and Phialophora verrucosa: Involvement with Antifungal Resistance

Patients with chromoblastomycosis (CBM) suffer chronic tissue lesions that are hard to treat. Considering that biofilm is the main growth lifestyle of several pathogens and it is involved with both virulence and resistance to antimicrobial drugs, we have investigated the ability of CBM fungi to produce this complex, organized and multicellular structure. Fonsecaea pedrosoi and Phialophora verrucosa conidial cells were able to adhere on a polystyrene abiotic substrate, differentiate into hyphae and produce a robust viable biomass containing extracellular matrix. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) showed the tridimensional architecture of the mature biofilms, revealing a dense network of interconnected hyphae, inner channels and amorphous extracellular polymeric material. Interestingly, the co-culture of each fungus with THP-1 macrophage cells, used as a biotic substrate, induced the formation of a mycelial trap covering and damaging the macrophages. In addition, the biofilm-forming cells of F. pedrosoi and P. verrucosa were more resistant to the conventional antifungal drugs than the planktonic-growing conidial cells. The efflux pump activities of P. verrucosa and F. pedrosoi biofilms were significantly higher than those measured in conidia. Taken together, the data pointed out the biofilm formation by CBM fungi and brought up a discussion of the relevance of studies about their antifungal resistance mechanisms.

Candida species detection in patients with chronic periodontitis: A systematic review and meta-analysis

OBJECTIVES

To assess the Candida species occurrence rate and concentration in periodontal pockets in chronic periodontitis (CP) by meta-analysis.

MATERIALS AND METHODS

A search was performed of articles published between January 1, 2010, and October 1, 2020, in English and in Russian, in the electronic databases MEDLINE-PubMed, Google Scholar, The Cochrane Library, ClinicalTrials.gov, Research Gate, eLIBRARY, and Cyberleninka (PROSPEROCRD42021234831). The odds ratio (OR), standardized mean difference (SMD), and 95% confidence interval (CI) were calculated using Review Manager 5.4.1 to compare the risk of CP when Candida spp. were detected in the gingival sulcus or periodontal pocket and to compare Candida spp. density counts in patients with CP and periodontally healthy patients.

RESULTS

Twenty-six studies were included in the systematic review and 11 were included in the meta-analysis. The results showed that Candida spp. may increase the chance of CP development by 1.76 times (OR = 1.76; 95% CI = 1.04-2.99; Z = 2.10; p = .04; I²  = 61%). More Candida spp. were found in patients with CP than in periodontally healthy patients (SMD = 1.58; 95% CI = 0.15-3.02; p = .03; I²  = 98%). No data were found relating to the statistically significant influence of Candida glabrata, Candida krusei and Candida tropicalis on CP development.

CONCLUSION

We found that Candida albicans insignificantly increased the risk of CP development but, due to the heterogeneity of the included studies, further research is necessary to determine the exact role of Candida spp. in the development and course of the inflammatory periodontal diseases.

The Role of Glycoside Hydrolases in S. gordonii and C. albicans Interactions

Candida albicans can coaggregate with Streptococcus gordonii and cocolonize in the oral cavity. Saliva provides a vital microenvironment for close interactions of oral microorganisms. However, the level of fermentable carbohydrates in saliva is not sufficient to support the growth of multiple species. Glycoside hydrolases (GHs) that hydrolyze glycoproteins are critical for S. gordonii growth in low-fermentable-carbohydrate environments such as saliva. However, whether GHs are involved in the cross-kingdom interactions between C. albicans and S. gordonii under such conditions remains unknown. In this study, C. albicans and S. gordonii were cocultured in heart infusion broth with a low level of fermentable carbohydrate. Planktonic growth, biofilm formation, cell aggregation, and GH activities of monocultures and cocultures were examined. The results revealed that the planktonic growth of cocultured S. gordonii in a low-carbohydrate environment was elevated, while that of cocultured C. albicans was reduced. The biomass of S. gordonii in dual-species biofilms was higher than that of monocultures, while that of cocultured C. albicans was decreased. GH activity was observed in S. gordonii, and elevated activity of GHs was detected in S. gordonii-C. albicans cocultures, with elevated expression of GH-related genes of S. gordonii. By screening a mutant library of C. albicans, we identified a tec1Δ/Δ mutant strain that showed reduced ability to promote the growth and GH activities of S. gordonii compared with the wild-type strain. Altogether, the findings of this study demonstrate the involvement of GHs in the cross-kingdom metabolic interactions between C. albicans and S. gordonii in an environment with low level of fermentable carbohydrates. IMPORTANCE Cross-kingdom interactions between Candida albicans and oral streptococci such as Streptococcus gordonii have been reported. However, their interactions in a low-fermentable-carbohydrate environment like saliva is not clear. The current study revealed glycoside hydrolase-related cross-kingdom communications between S. gordonii and C. albicans under the low-fermentable-carbohydrate condition. We demonstrate that C. albicans can promote the growth and metabolic activities of S. gordonii by elevating the activities of cell-wall-anchored glycoside hydrolases of S. gordonii. C. albicans gene TEC1 is critical for this cross-kingdom metabolic communication.

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.

The Role of Candida albicans Virulence Factors in the Formation of Multispecies Biofilms With Bacterial Periodontal Pathogens

Periodontal disease depends on the presence of different microorganisms in the oral cavity that during the colonization of periodontal tissues form a multispecies biofilm community, thus allowing them to survive under adverse conditions or facilitate further colonization of host tissues. Not only numerous bacterial species participate in the development of biofilm complex structure but also fungi, especially Candida albicans, that often commensally inhabits the oral cavity. C. albicans employs an extensive armory of various virulence factors supporting its coexistence with bacteria resulting in successful host colonization and propagation of infection. In this article, we highlight various aspects of individual fungal virulence factors that may facilitate the collaboration with the associated bacterial representatives of the early colonizers of the oral cavity, the bridging species, and the late colonizers directly involved in the development of periodontitis, including the “red complex” species. In particular, we discuss the involvement of candidal cell surface proteins—typical fungal adhesins as well as originally cytosolic “moonlighting” proteins that perform a new function on the cell surface and are also present within the biofilm structures. Another group of virulence factors considered includes secreted aspartic proteases (Sap) and other secreted hydrolytic enzymes. The specific structure of the candidal cell wall, dynamically changing during morphological transitions of the fungus that favor the biofilm formation, is equally important and discussed. The non-protein biofilm-composing factors also show dynamic variability upon the contact with bacteria, and their biosynthesis processes could be involved in the stability of mixed biofilms. Biofilm-associated changes in the microbe communication system using different quorum sensing molecules of both fungal and bacterial cells are also emphasized in this review. All discussed virulence factors involved in the formation of mixed biofilm pose new challenges and influence the successful design of new diagnostic methods and the application of appropriate therapies in periodontal diseases.

An In Vitro Evaluation of Denture Cleansing Regimens against a Polymicrobial Denture Biofilm Model

Denture stomatitis (DS) is an inflammatory disease resulting from a polymicrobial biofilm perturbation at the denture surface–palatal mucosa interface. Recommendations made by dental health care professionals often lack clarity for appropriate denture cleaning. This study investigated the efficacy of brushing with off-the-shelf denture cleanser (DC) tablets (Poligrip^®) vs. two toothpastes (Colgate^® and Crest^®) in alleviating the viable microorganisms (bacteria and fungi) in an in vitro denture biofilm model. Biofilms were grown on poly(methyl)methacrylate (PMMA) discs, then treated daily for 7 days with mechanical disruption (brushing), plus Poligrip^® DC, Colgate^® or Crest^® toothpastes. Weekly treatment with Poligrip^® DC on day 7 only was compared to daily modalities. All treatment parameters were processed to determine viable colony forming units for bacteria and fungi using the Miles and Misra technique, and imaged by confocal laser scanning microscopy (CLSM). Brushing with daily DC therapy was the most effective treatment in reducing the viable biofilm over 7 days of treatment. Brushing only was ineffective in controlling the viable bioburden, which was confirmed by CLSM imaging. This data indicates that regular cleansing of PMMA with DC was best for polymicrobial biofilms.

Hydrogen peroxide potentiates antimicrobial photodynamic therapy in eliminating Candida albicans and Streptococcus mutans dual-species biofilm from denture base

BACKGROUND

Candida albicans (C.albicans) is the primary pathogen of denture biofilm. Moreover, it could establish a cross-kingdom relationship with bacteria to enhance its virulence and resistance to antifungal drugs. This study aimed to investigate the efficacy of antimicrobial photodynamic therapy (aPDT) in combination with hydrogen peroxide (H₂O₂) against C.albicans and Streptococcus mutans (S.mutans) dual-species biofilm formed on polymethyl methacrylate (PMMA) disk, and explore its involved mechanisms.

METHODS

C.albicans and S.mutans were grown on PMMA disk for 48 h to form biofilm and received different treatments. The treatments included:1) phosphate-buffered saline (PBS) group,2) 100 mM H₂O₂ group,3) aPDT group,4) aPDT+ H₂O₂ and 5) H₂O₂+aPDT group. Colony forming units (CFU), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and scanning electron microscope (SEM) were used to evaluate the antimicrobial effects. Extracellular polysaccharide substance (EPS) production and observation, cell permeability of biofilm, and uptake of toluidine blue O (TBO) by biofilm were assessed to investigate the involved mechanism.

RESULTS

There was no significant difference between PBS group and H₂O₂ group in viable microorganisms and metabolic activity of biofilm. The treatment protocols containing aPDT group reduced microorganism numbers and metabolic activity when compared to PBS group or H₂O₂ group (P<0.05). H₂O₂+aPDT treatment showed the highest antimicrobial efficacy in comparison with other treatments (P<0.05). Pretreatment with H₂O₂ could decrease EPS production and enhance cell permeability, leading to increased TBO uptake in biofilm.

CONCLUSION

Pretreatment with H₂O₂ improved aPDT efficiency in eliminating dual-species biofilm from PMMA disk by reducing EPS amount, enhancing cell permeability, and increasing TBO uptake.

Investigating the Transcriptome of Candida albicans in a Dual-Species Staphylococcus aureus Biofilm Model

Candida albicans is an opportunistic pathogen found throughout multiple body sites and is frequently co-isolated from infections of the respiratory tract and oral cavity with Staphylococcus aureus. Herein we present the first report of the effects that S. aureus elicits on the C. albicans transcriptome. Dual-species biofilms containing S. aureus and C. albicans mutants defective in ALS3 or ECE1 were optimised and characterised, followed by transcriptional profiling of C. albicans by RNA-sequencing (RNA-seq). Altered phenotypes in C. albicans mutants revealed specific interaction profiles between fungus and bacteria. The major adhesion and virulence proteins Als3 and Ece1, respectively, were found to have substantial effects on the Candida transcriptome in early and mature biofilms. Despite this, deletion of ECE1 did not adversely affect biofilm formation or the ability of S. aureus to interact with C. albicans hyphae. Upregulated genes in dual-species biofilms corresponded to multiple gene ontology terms, including those attributed to virulence, biofilm formation and protein binding such as ACE2 and multiple heat-shock protein genes. This shows that S. aureus pushes C. albicans towards a more virulent genotype, helping us to understand the driving forces behind the increased severity of C. albicans-S. aureus infections.

Recurrent Vulvovaginal Candidiasis: a Dynamic Interkingdom Biofilm Disease of Candida and Lactobacillus

Despite the strikingly high worldwide prevalence of vulvovaginal candidiasis (VVC), treatment options for recurrent VVC (RVVC) remain limited, with many women experiencing failed clinical treatment with frontline azoles. Further, the cause of onset and recurrence of disease is largely unknown, with few studies identifying potential mechanisms of treatment failure. This study aimed to assess a panel of clinical samples from healthy women and those with RVVC to investigate the influence of Candida, the vaginal microbiome, and how their interaction influences disease pathology. 16S rRNA sequencing characterized disease by a reduction in specific health-associated Lactobacillus species, such as Lactobacillus crispatus, coupled with an increase in Lactobacillus iners. In vitro analysis showed that Candida albicans clinical isolates are capable of heterogeneous biofilm formation, and we found the presence of hyphae and C. albicans aggregates in vaginal lavage fluid. Additionally, the ability of Lactobacillus to inhibit C. albicans biofilm formation and biofilm-related gene expression was demonstrated. Using RNA sequencing technology, we were able to identify a possible mechanism by which L. crispatus may contribute to re-establishing a healthy vaginal environment through amino acid acquisition from C. albicans. This study highlights the potential formation and impact of Candida biofilms in RVVC. Additionally, it suggests that RVVC is not entirely due to an arbitrary switch in C. albicans from commensal to pathogen and that understanding interactions between this yeast and vaginal Lactobacillus species may be crucial to elucidating the cause of RVVC and developing appropriate therapies. IMPORTANCE RVVC is a significant burden, both economically and for women's health, but its prevalence is poorly documented globally due to the levels of self-treatment. Identifying triggers for development and recurrence of VVC and the pathogenesis of the microbes involved could considerably improve prevention and treatment options for women with recurrent, azole-resistant cases. This study therefore aimed to examine the interkingdom dynamics from healthy women and those with RVVC using next-generation sequencing techniques and to further investigate the molecular interactions between C. albicans and L. crispatus in a relevant biofilm coculture system.

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.

pH-Responsive copolymer micelles to enhance itraconazole efficacy against Candida albicans biofilms

Candida albicans (C. albicans) is a common fungal pathogen causing both localised and systemic infections. The majority of these infections are promoted by biofilm formation, providing a protective matrix for the embedded fungi thereby evading the host immune defence and promoting resistance against anti-mycotic agents. In this study, pH-responsive micellar systems based on poly-(ethylene glycol) ethyl ether methacrylate (PEGMA) and poly 2-(diethylamino) ethyl methacrylate (DEAEMA) block-copolymers of P(PEGMA-b-DEAEMA) were specifically developed and loaded with the antifungal itraconazole (ICZ) to defeat C. albicans biofilms. The P(PEGMA-b-DEAEMA) di-block polymer micelles demonstrated a particle size of 55 ± 6 nm and high ICZ loads (12.0 ± 0.5% w/w). Within the biofilm's acidic microenvironment, tertiary amines of the pH-sensitive DEAEMA block are protonated, altering their conformation and enhancing the release of the micellar contents. Encapsulation of ICZ within micelles significantly enhanced the activity against C. albicans biofilms, with a significant reduction in the biofilm biomass (>50%) and in the number of viable cells (2.4 Log reduction) achieved, compared with the non-encapsulated ICZ. Confocal microscopy revealed a high affinity and accumulation of the micelles in C. albicans biofilms as a result of their size and specific electrostatic interaction, hence their improved activity. P(PEGMA-b-DEAEMA) based pH-responsive micelles offer significant potential as antifungal carriers for controlling Candida infections.

Candida albicans as an Essential "Keystone" Component within Polymicrobial Oral Biofilm Models?

Background: Existing standardized biofilm assays focus on simple mono-species or bacterial-only models. Incorporating Candida albicans into complex biofilm models can offer a more appropriate and relevant polymicrobial biofilm for the development of oral health products. Aims: This study aimed to assess the importance of interkingdom interactions in polymicrobial oral biofilm systems with or without C. albicans, and test how these models respond to oral therapeutic challenges in vitro. Materials and Methods: Polymicrobial biofilms (two models containing 5 and 10 bacterial species, respectively) were created in parallel in the presence and absence of C. albicans and challenged using clinically relevant antimicrobials. The metabolic profiles and biomasses of these complex biofilms were estimated using resazurin dye and crystal violet stain, respectively. Quantitative PCR was utilized to assess compositional changes in microbial load. Additional assays, for measurements of pH and lactate, were included to monitor fluctuations in virulence "biomarkers." Results: An increased level of metabolic activity and biomass in the presence of C. albicans was observed. Bacterial load was increased by more than a factor of 10 in the presence of C. albicans. Assays showed inclusion of C. albicans impacted the biofilm virulence profiles. C. albicans did not affect the biofilms' responses to the short-term incubations with different treatments. Conclusions: The interkingdom biofilms described herein are structurally robust and exhibit all the hallmarks of a reproducible model. To our knowledge, these data are the first to test the hypothesis that yeasts may act as potential "keystone" components of oral biofilms.

Filling the Void: An Optimized Polymicrobial Interkingdom Biofilm Model for Assessing Novel Antimicrobial Agents in Endodontic Infection

There is a growing realization that endodontic infections are often polymicrobial, and may contain Candida spp. Despite this understanding, the development of new endodontic irrigants and models of pathogenesis remains limited to mono-species biofilm models and is bacterially focused. The purpose of this study was to develop and optimize an interkingdom biofilm model of endodontic infection and use this to test suitable anti-biofilm actives. Biofilms containing Streptococcus gordonii, Fusobacterium nucleatum, Porphyromonas gingivalis, and Candida albicans were established from ontological analysis. Biofilms were optimized in different media and atmospheric conditions, prior to quantification and imaging, and subsequently treated with chlorhexidine, EDTA, and chitosan. These studies demonstrated that either media supplemented with serum were equally optimal for biofilm growth, which were dominated by S. gordonii, followed by C. albicans. Assessment of antimicrobial activity showed significant effectiveness of each antimicrobial, irrespective of serum. Chitosan was most effective (3 log reduction), and preferentially targeted C. albicans in both biofilm treatment and inhibition models. Chitosan was similarly effective at preventing biofilm growth on a dentine substrate. This study has shown that a reproducible and robust complex interkingdom model, which when tested with the antifungal chitosan, supports the notion of C. albicans as a key structural component.

Bismuth nanoparticles obtained by a facile synthesis method exhibit antimicrobial activity against Staphylococcus aureus and Candida albicans

Background

Bismuth compounds are known for their activity against multiple microorganisms; yet, the antibiotic properties of bismuth nanoparticles (BiNPs) remain poorly explored. The objective of this work is to further the research of BiNPs for nanomedicine-related applications. Stable Polyvinylpyrrolidone (PVP)-coated BiNPs were produced by a chemical reduction process, in less than 30 min.

Results

We produced stable, small, spheroid PVP-coated BiNPs with a crystalline organization. The PVP-BiNPs showed potent antibacterial activity against the pathogenic bacterium Staphylococcus aureus and antifungal activity against the opportunistic pathogenic yeast Candida albicans, both under planktonic and biofilm growing conditions.

Conclusions

Our results indicate that BiNPs represent promising antimicrobial nanomaterials, and this facile synthetic method may allow for further investigation of their activity against a variety of pathogenic microorganisms.

The Proteome of Community Living Candida albicans Is Differentially Modulated by the Morphologic and Structural Features of the Bacterial Cohabitants

Candida albicans is a commensal polymorphic and opportunistic fungus, which usually resides as a small community in the oral cavities of a majority of humans. The latter eco-system presents this yeast varied opportunities for mutualistic interactions with other cohabitant oral bacteria, that synergizes its persistence and pathogenicity. Collectively, these communities live within complex plaque biofilms which may adversely affect the oral health and increase the proclivity for oral candidiasis. The proteome of such oral biofilms with myriad interkingdom interactions are largely underexplored. Herein, we employed limma differential expression analysis, and cluster analysis to explore the proteomic interactions of C. albicans biofilms with nine different common oral bacterial species, Aggregatibacter actinomycetemcomitans, Actinomyces naeslundii, Fusobacterium nucleatum, Enterococcus faecalis, Porphyromonas gingivalis, Streptococcus mutants, Streptococcus sanguinis, Streptococcus mitis, and Streptococcus sobrinus. Interestingly, upon exposure of C. albicans biofilms to the foregoing heat-killed bacteria, the proteomes of the fungus associated with cellular respiration, translation, oxidoreductase activity, and ligase activity were significantly altered. Subsequent differential expression and cluster analysis revealed the subtle, yet significant alterations in the C. albicans proteome, particularly on exposure to bacteria with dissimilar cell morphologies, and Gram staining characteristics.

Inhibition of Mixed Biofilms of Candida albicans and Methicillin-Resistant Staphylococcus aureus by Positively Charged Silver Nanoparticles and Functionalized Silicone Elastomers

Both bacterial and fungal organisms display the ability to form biofilms; however, mixed bacterial/fungal biofilms are particularly difficult to control and eradicate. The opportunistic microbial pathogens Candida albicans and Staphylococcus aureus are among the most frequent causative agents of healthcare-acquired infections, and are often co-isolated forming mixed biofilms, especially from contaminated catheters. These mixed species biofilms display a high level of antibiotic resistance; thus, these infections are challenging to treat resulting in excess morbidity and mortality. In the absence of effective conventional antibiotic treatments, nanotechnology-based approaches represent a promising alternative for the treatment of highly recalcitrant polymicrobial biofilm infections. Our group has previously reported on the activity of pure positively charged silver nanoparticles synthesized by a novel microwave technique against single-species biofilms of C. albicans and S. aureus. Here, we have expanded our observations to demonstrate that that silver nanoparticles display dose-dependent activity against dual-species C. albicans/S. aureus biofilms. Moreover, the same nanoparticles were used to functionalize catheter materials, leading to the effective inhibition of the mixed fungal/bacterial biofilms. Overall, our results indicate the potent activity of silver nanoparticles against these cross-kingdom biofilms. More studies are warranted to examine the ability of functionalized catheters in the prevention of catheter-related bloodstream infections.

Cross-Kingdom Cell-to-Cell Interactions in Cariogenic Biofilm Initiation

Candida albicans is known to form polymicrobial biofilms with various Streptococcus spp., including mitis and mutans group streptococci. Streptococcus gordonii (mitis group) has been shown to bind avidly to C. albicans hyphae via direct cell-to-cell interaction, while the cariogenic pathogen Streptococcus mutans (mutans group) interacts with the fungal cells via extracellular glucans. However, the biophysical properties of these cross-kingdom interactions at the single-cell level during the early stage of biofilm formation remain understudied. Here, we examined the binding forces between S. mutans (or S. gordonii) and C. albicans in the presence and absence of in situ glucans on the fungal surface using single-cell atomic force microscopy and their influence on biofilm initiation and subsequent development under cariogenic conditions. The data show that S. gordonii binding force to the C. albicans surface is significantly higher than that ofS. mutans to the fungal surface (~2-fold). However, S. mutans binding forces are dramatically enhanced when the C. albicans cell surface is locally coated with extracellular glucans (~6-fold vs. uncoated C. albicans), which vastly exceeds the forces between S. gordonii andC. albicans. The enhanced binding affinity of S. mutans to glucan-coated C. albicans resulted in a larger structure during early biofilm initiation compared to S. gordonii-C. albicans biofilms. Ultimately, this resulted in S. mutans dominance composition in the 3-species biofilm model under cariogenic conditions. This study provides a novel biophysical aspect of Candida-streptococcal interaction whereby extracellular glucans may selectively favor S. mutans binding interactions with C. albicans during cariogenic biofilm development.

Biofilm growth and IL-8 & TNF-α-inducing properties of Candida albicans in the presence of oral gram-positive and gram-negative bacteria

Background

Interaction of C. albicans with oral bacteria is crucial for its persistence, but also plays a potential role in the infection process. In the oral cavity, it grows as part of dental plaque biofilms. Even though growth and interaction of C. albicans with certain bacterial species has been studied, little is known about its biofilm growth in vitro in the simultaneous presence of Gram-negative and Gram-positive bacteria. The aim was to evaluate the growth of C. albicans in polymicrobial biofilms comprising oral Gram-negative and Gram-positive bacteria. Further, we also aimed to assess the potential of C. albicans in the Candida-bacteria polymicrobial biofilm to elicit cytokine gene expression and cytokine production from human blood cells.

Results

C. albicans cell counts increased significantly up to 48 h in polymicrobial biofilms (p < 0.05), while the bacterial counts in the same biofilms increased only marginally as revealed by qPCR absolute quantification. However, the presence of bacteria in the biofilm did not seem to affect the growth of C. albicans. Expression of IL-8 gene was significantly (p < 0.05) higher upon stimulation from biofilm-supernatants than from biofilms in polymicrobial setting. On the contrary, TNF-α expression was significantly higher in biofilms than in supernatants but was very low (1–4 folds) in the monospecies biofilm of C. albicans. ELISA cytokine quantification data was in agreement with mRNA expression results.

Conclusion

Persistence and enhanced growth of C. albicans in polymicrobial biofilms may imply that previously reported antagonistic effect of A. actinomycetemcomitans was negated. Increased cytokine gene expression and cytokine production induced by Candida-bacteria polymicrobial biofilms and biofilm supernatants suggest that together they possibly exert an enhanced stimulatory effect on IL-8 and TNF-α production from the host.

Dynamics of Dissolution, Killing, and Inhibition of Dental Plaque Biofilm

The present study aims to establish a standardized model that makes it possible to evaluate the dynamic dissolution of biofilm, killing of biofilm microbes and inhibition of growth of biofilm by disinfecting solutions. Biofilm was grown from dental plaque bacteria on collagen-coated hydroxyapatite (HA) disks for 3 days or 3 weeks under anaerobic conditions. Biofilms were stained with the LIVE/DEAD viability stain and subjected to sterile water, 2% sodium hypochlorite (NaOCl), 6% NaOCl, or 2% chlorhexidine (CHX) for 32 min. Dynamic change in fluorescence on bacterial cells and extracellular polymeric substance (EPS) during the exposure was analyzed using Alexa Fluor 647-labeled dextran conjugate and a live-cell imaging confocal laser scanning microscopy (LC-CLSM). The biofilm structures after treatments were visualized by scanning electron microscopy (SEM). The treated biofilms on HA disks were collected and subjected to colony forming unit (CFU) counting. Another set of sterile HA disks were coated with CHX prior to the monitoring of plaque biofilm growth for 12 h. The LC-CLSM results showed that NaOCl dissolved biofilm effectively, more so at a higher concentration and longer exposure time. Six percent NaOCl was the most effective at dissolving and killing bacteria (e.g., 99% bacterial reduction in 3-day-old biofilm and 95% bacterial reduction in 3-week-old biofilm in 32 min) followed by 2% NaOCl and CHX. Sodium hypochlorite dissolved over 99.9% of the EPS whereas CHX only slightly reduced the EPS biovolume in 32 min. CFU results indicated that the dispersed biofilm bacteria are more resistant than planktonic bacteria to disinfectants. SEM showed the disruption of biofilm after exposures to CHX and NaOCl. The use of 2% CHX and sterile water did not result in biofilm dissolution. However, prior exposure of the HA disks to 2 and 0.2% CHX for 3 min prevented biofilm from growing on the HA disk surfaces for at least 12 h. This new platform has the potential to aid in a better understanding of the antibiofilm properties of oral disinfectants.

A nanocarrier system that potentiates the effect of miconazole within different interkingdom biofilms

Background

Novel and new therapeutic strategies capable of enhancing the efficacy of existing antimicrobials is an attractive proposition to meet the needs of society.

Objective

This study aimed to evaluate the potentiating effect of a miconazole (MCZ) nanocarrier system, incorporated with iron oxide nanoparticles (IONPs) and chitosan (CS) (IONPs-CS-MCZ). This was tested on three representative complex interkingdom oral biofilm models (caries, denture and gingivitis).

Materials and methods

The planktonic and sessile minimum inhibitory concentrations (MICs) of IONPs-CS-MCZ against different Candida albicans strains were determined, as well as against all represented bacterial species that formed within the three biofilm models. Biofilms were treated for 24 hours with the IONPs-CS nanocarrier system containing MCZ at 64 mg/L, and characterized using a range of bioassays for quantitative and qualitative assessment.

Results

MIC results generally showed that IONPs-CS-MCZ was more effective than MCZ alone. IONPs-CS-MCZ also promoted reductions in the number of CFUs, biomass and metabolic activity of the representative biofilms, as well as altering biofilm ultrastructure when compared to untreated biofilms. IONPs-CS-MCZ affected the composition and reduced the CFEs for most of the microorganisms present in the three evaluated biofilms. In particular, the proportion of streptococci in the biofilm composition were reduced in all three models, whilst Fusobacterium spp. percentage reduced in the gingivitis and caries models, respectively.

Conclusion

In conclusion, the IONPs-CS-MCZ nanocarrier was efficient against three in vitro models of pathogenic oral biofilms, showing potential to possibly interfere in the synergistic interactions among fungal and bacterial cells within polymicrobial consortia.

Nanovectorized Microalgal Extracts to Fight Candida albicans and Cutibacterium acnes Biofilms: Impact of Dual-Species Conditions

Biofilm-related infections are a matter of concern especially because of the poor susceptibility of microorganisms to conventional antimicrobial agents. Innovative approaches are needed. The antibiofilm activity of extracts of cyanobacteria Arthrospira platensis, rich in free fatty acids, as well as of extract-loaded copper alginate-based nanocarriers, were studied on single- and dual-species biofilms of Candida albicans and Cutibacterium acnes. Their ability to inhibit the biofilm formation and to eradicate 24 h old biofilms was investigated. Concentrations of each species were evaluated using flow cytometry. Extracts prevented the growth of C. acnes single-species biofilms (inhibition > 75% at 0.2 mg/mL) but failed to inhibit preformed biofilms. Nanovectorised extracts reduced the growth of single-species C. albicans biofilms (inhibition > 43% at 0.2 mg/mL) while free extracts were weakly or not active. Nanovectorised extracts also inhibited preformed C. albicans biofilms by 55% to 77%, whereas the corresponding free extracts were not active. In conclusion, even if the studied nanocarrier systems displayed promising activity, especially against C. albicans, their efficacy against dual-species biofilms was limited. This study highlighted that working in such polymicrobial conditions can give a more objective view of the relevance of antibiofilm strategies by taking into account interspecies interactions that can offer additional protection to microbes.

Bismuth nanoparticles obtained by a facile synthesis method exhibit antimicrobial activity against Staphylococcus aureus and Candida albicans

BACKGROUND

Bismuth compounds are known for their activity against multiple microorganisms; yet, the antibiotic properties of bismuth nanoparticles (BiNPs) remain poorly explored. The objective of this work is to further the research of BiNPs for nanomedicine-related applications. Stable Polyvinylpyrrolidone (PVP)-coated BiNPs were produced by a chemical reduction process, in less than 30 min.

RESULTS

We produced stable, small, spheroid PVP-coated BiNPs with a crystalline organization. The PVP-BiNPs showed potent antibacterial activity against the pathogenic bacterium Staphylococcus aureus and antifungal activity against the opportunistic pathogenic yeast Candida albicans, both under planktonic and biofilm growing conditions.

CONCLUSIONS

Our results indicate that BiNPs represent promising antimicrobial nanomaterials, and this facile synthetic method may allow for further investigation of their activity against a variety of pathogenic microorganisms.

Protocol optimization for a fast, simple and economical chemical reduction synthesis of antimicrobial silver nanoparticles in non-specialized facilities

OBJECTIVE

Silver nanoparticles (AgNPs) can be difficult or expensive to obtain or synthesize for laboratories in resource-limited facilities. The purpose of this work was to optimize a synthesis method for a fast, facile, and cost-effective synthesis of AgNPs with antimicrobial activity, which can be readily implemented in non-specialized facilities and laboratories.

RESULTS

The optimized method uses a rather simple and rapid chemical reduction process that involves the addition of a polyvinylpyrrolidone solution to a warmed silver nitrate solution under constant vigorous stirring, immediately followed by the addition of sodium borohydride. The total synthesis time is less than 15 min. The obtained AgNPs exhibit an aspect ratio close to 1, with an average size of 6.18 ± 5 nm. AgNPs displayed potent antimicrobial activity, with Minimal Inhibitory Concentration values of ≤ 4 µg mL^-1 for Staphylococcus aureus and ≤ 2 µg mL^-1 for Candida albicans. The resulting method is robust and highly reproducible, as demonstrated by the characterization of AgNPs from different rounds of syntheses and their antimicrobial activity.

Recent progress in experimental and human disease-associated multi-species biofilms

Human bodies are colonized by trillions of microorganisms, which are often referred to as human microbiota and play important roles in human health. Next generation sequencing studies have established links between the genetic content of human microbiota and various human diseases. However, it remains largely unknown about the spatial organizations and interspecies interactions of individual species within the human microbiota. Bacterial cells tend to form surface-attached biofilms in many natural environments, which enable intercellular communications and interactions in a microbial ecosystem. In this review, we summarize the recent progresses on the experimental and human disease-associated multi-species biofilm studies. We hypothesize that engineering biofilm structures and interspecies interactions might provide a tool for manipulating the composition and function of human microbiota.

Disparate Candida albicans Biofilm Formation in Clinical Lipid Emulsions Due to Capric Acid-Mediated Inhibition

Receipt of parenteral nutrition (PN) remains an independent risk factor for developing catheter-related bloodstream infections (CR-BSI) caused by fungi, including by the polymorphic fungus Candida albicans, which is notoriously adept at forming drug-resistant biofilm structures. Among a variety of macronutrients, PN solutions contain lipid emulsions to supply daily essential fats and are often delivered via central venous catheters (CVCs). Therefore, using an in vitro biofilm model system, we sought to determine whether various clinical lipid emulsions differentially impacted biofilm growth in C. albicans We observed that the lipid emulsions Intralipid and Omegaven both stimulated C. albicans biofilm formation during growth in minimal medium or a macronutrient PN solution. Conversely, Smoflipid inhibited C. albicans biofilm formation by approximately 50%. Follow-up studies revealed that while Smoflipid did not impair C. albicans growth, it did significantly inhibit hypha formation and hyphal elongation. Moreover, growth inhibition could be recapitulated in Intralipid when supplemented with capric acid-a fatty acid present in Smoflipid but absent in Intralipid. Capric acid was also found to dose dependently inhibit C. albicans biofilm formation in PN solutions. This is the first study to directly compare different clinical lipid emulsions for their capacity to affect C. albicans biofilm growth. Results derived from this study necessitate further research regarding different lipid emulsions and rates of fungus-associated CR-BSIs.

Candida albicans cell wall integrity transcription factors regulate polymicrobial biofilm formation with Streptococcus gordonii

Polymicrobial biofilms play important roles in oral and systemic infections. The oral plaque bacterium Streptococcus gordonii is known to attach to the hyphal cell wall of the fungus Candida albicans to form corn-cob like structures in biofilms. However, the role of C. albicans in formation of polymicrobial biofilms is not completely understood. The objective of this study was to determine the role of C. albicans transcription factors in regulation of polymicrobial biofilms and antibiotic tolerance of S. gordonii. The proteins secreted by C. albicans and S. gordonii in mixed planktonic cultures were determined using mass spectrometry. Antibiotic tolerance of S. gordonii to ampicillin and erythromycin was determined in mixed cultures and mixed biofilms with C. albicans. Additionally, biofilm formation of S. gordonii with C. albicans knock-out mutants of 45 transcription factors that affect cell wall integrity, filamentous growth and biofilm formation was determined. Furthermore, these mutants were also screened for antibiotic tolerance in mixed biofilms with S. gordonii. Analysis of secreted proteomes resulted in the identification of proteins being secreted exclusively in mixed cultures. Antibiotic testing showed that S. gordonii had significantly increased survival in mixed planktonic cultures with antibiotics as compared to single cultures. C. albicans mutants of transcription factors Sfl2, Brg1, Leu3, Cas5, Cta4, Tec1, Tup1, Rim101 and Efg1 were significantly affected in mixed biofilm formation. Also mixed biofilms of S. gordonii with mutants of C. albicans transcription factors, Tec1 and Sfl2, had significantly reduced antibiotic tolerance as compared to control cultures. Our data indicates that C. albicans may have an important role in mixed biofilm formation as well as antibiotic tolerance of S. gordonii in polymicrobial biofilms. C. albicans may play a facilitating role than being just an innocent bystander in oral biofilms and infections.

Contributions of Candida albicans Dimorphism, Adhesive Interactions, and Extracellular Matrix to the Formation of Dual-Species Biofilms with Streptococcus gordonii

Microbial communities have a great impact in health and disease. C. albicans interacts with multiple microorganisms in the oral cavity, frequently forming polymicrobial biofilms. We report on the synergistic interactions between C. albicans and the Gram-positive bacterium S. gordonii, for which we have examined the different contributions of adhesive interactions, filamentation, and the extracellular matrix to the formation of dual-species biofilms. Our results demonstrate that growth in the presence of the bacterium can restore the biofilm-forming ability of different C. albicans mutant strains with defects in adhesion and filamentation. The mixed-species biofilms also show high levels of resistance to antibacterial and antifungal antibiotics, and our results indicate that the fungal biofilm matrix protects bacterial cells within these mixed-species biofilms. Our observations add to a growing body of evidence indicating a high level of complexity in the reciprocal interactions and consortial behavior of fungal/bacterial biofilms.

Fungal and bacterial populations coexist in the oral cavity, frequently forming mixed-species biofilms that complicate treatment against polymicrobial infections. However, despite relevance to oral health, the bidirectional interactions between these microbial populations are poorly understood. In this study, we aimed to elucidate the mechanisms underlying the interactions between the fungal species Candida albicans and the bacterial species Streptococcus gordonii as they coexist in mixed-species biofilms. Specifically, the interactions of different C. albicans mutant strains deficient in filamentation (efg1Δ/Δ and brg1Δ/Δ), adhesive interactions (als3Δ/Δ and bcr1Δ/Δ), and production of matrix exopolymeric substances (EPS) (kre5Δ/Δ, mnn9Δ/Δ, rlm1Δ/Δ, and zap1Δ/Δ) were evaluated with S. gordonii under different conditions mimicking the environment in the oral cavity. Interestingly, our results revealed that growth of the biofilm-deficient C. albicansals3Δ/Δ and bcr1Δ/Δ mutant strains in synthetic saliva or with S. gordonii restored their biofilm-forming ability. Moreover, challenging previous observations indicating an important role of morphogenetic conversions in the interactions between these two species, our results indicated a highly synergistic interaction between S. gordonii and the C. albicans filamentation-deficient efg1Δ/Δ and brg1Δ/Δ deletion mutants, which was particularly noticeable when the mixed biofilms were grown in synthetic saliva. Importantly, dual-species biofilms were found to exhibit increase in antimicrobial resistance, indicating that components of the fungal exopolymeric material confer protection to streptococcal cells against antibacterial treatment. Collectively, these findings unravel a high degree of complexity in the interactions between C. albicans and S. gordonii in mixed-species biofilms, which may impact homeostasis in the oral cavity.

A Multispecies Biofilm In Vitro Screening Model of Dental Caries for High-Throughput Susceptibility Testing

There is a current need to develop and optimize new therapeutics for the treatment of dental caries, but these efforts are limited by the relatively low throughput of relevant in vitro models. The aim of this work was to bridge the 96-well microtiter plate system with a relevant multispecies dental caries model that could be reproducibly grown to allow for the high-throughput screening of anti-biofilm therapies. Various media and inoculum concentrations were assessed using metabolic activity, biomass, viability, and acidity assays to determine the optimal laboratory-controlled conditions for a multispecies biofilm composed of Streptococcus gordonii, Streptococcus mutans, and Candida albicans. The selected model encompasses several of the known fundamental characteristics of dental caries-associated biofilms. The 1:1 RPMI:TSBYE 0.6% media supported the viability and biomass production of mono- and multispecies biofilms best. Kinetic studies over 48 h in 1:1 RPMI:TSBYE 0.6% demonstrated a stable biofilm phase between 10 and 48 h for all mono- and multispecies biofilms. The 1:1:0.1 S. gordonii: S. mutans: C. albicans multispecies biofilm in 1:1 RPMI:TSBYE 0.6% is an excellent choice for a high-throughput multispecies model of dental caries. This high-throughput multispecies model can be used for screening novel therapies and for better understanding the treatment effects on biofilm interactions and stability.

Salt-Tolerant Antifungal and Antibacterial Activities of the Corn Defensin ZmD32

Pathogenic microbes are developing resistance to established antibiotics, making the development of novel antimicrobial molecules paramount. One major resource for discovery of antimicrobials is the arsenal of innate immunity molecules that are part of the first line of pathogen defense in many organisms. Gene encoded cationic antimicrobial peptides are a major constituent of innate immune arsenals. Many of these peptides exhibit potent antimicrobial activity in vitro. However, a major hurdle that has impeded their development for use in the clinic is the loss of activity at physiological salt concentrations, attributed to weakening of the electrostatic interactions between the cationic peptide and anionic surfaces of the microbial cells in the presence of salt. Using plant defensins we have investigated the relationship between the charge of an antimicrobial peptide and its activity in media with elevated salt concentrations. Plant defensins are a large class of antifungal peptides that have remarkable stability at extremes of pH and temperature as well as resistance to protease digestion. A search of a database of over 1200 plant defensins identified ZmD32, a defensin from Zea mays, with a predicted charge of +10.1 at pH 7, the highest of any defensin in the database. Recombinant ZmD32 retained activity against a range of fungal species in media containing elevated concentrations of salt. In addition, ZmD32 was active against Candida albicans biofilms as well as both Gram negative and Gram-positive bacteria. This broad spectrum antimicrobial activity, combined with a low toxicity on human cells make ZmD32 an attractive lead for development of future antimicrobial molecules.

Candida Interactions with the Oral Bacterial Microbiota

The human oral cavity is normally colonized by a wide range of microorganisms, including bacteria, fungi, Archaea, viruses, and protozoa. Within the different oral microenvironments these organisms are often found as part of highly organized microbial communities termed biofilms, which display consortial behavior. Formation and maintenance of these biofilms are highly dependent on the direct interactions between the different members of the microbiota, as well as on the released factors that influence the surrounding microbial populations. These complex biofilm dynamics influence oral health and disease. In the latest years there has been an increased recognition of the important role that interkingdom interactions, in particular those between fungi and bacteria, play within the oral cavity. Candida spp., and in particular C. albicans, are among the most important fungi colonizing the oral cavity of humans and have been found to participate in these complex microbial oral biofilms. C. albicans has been reported to interact with individual members of the oral bacterial microbiota, leading to either synergistic or antagonistic relationships. In this review we describe some of the better characterized interactions between Candida spp. and oral bacteria.

Cutibacterium acnes protects Candida albicans from the effect of micafungin in biofilms

The aim of this study was to investigate the ability of Candida albicans and Cutibacterium acnes to grow together as a polymicrobial biofilm in vitro and to examine the influence of C. acnes on C. albicans susceptibility to micafungin. Mature 72-h-old single-species biofilms of C. albicans and polymicrobial biofilms involving both C. albicans and C. acnes were formed in brain-heart infusion and were observed by scanning electronic microscopy. Moreover, 24-h-old single-species and polymicrobial biofilms were treated for 24 h with micafungin (concentrations ranging from 0.75 mg/L to 12 mg/L) and the antibiofilm activity of micafungin was evaluated on fungal cells by flow cytometry following addition of propidium iodide. The results showed that C. albicans and C. acnes formed a polymicrobial biofilm in the tested conditions and that bacterial presence did not modify fungal viability. Micafungin induced a fungal mortality rate ranging from 70-95% in C. albicans single-species biofilms and from 35-40% in C. acnes-C. albicans polymicrobial biofilms. Mortality induced by micafungin was significantly reduced (P < 0.05 for micafungin at 6 mg/L and P < 0.001 for other micafungin concentrations) in polymicrobial conditions compared with single-species biofilms. In conclusion, this study showed that C. albicans and C. acnes are able to form polymicrobial biofilms together in a synergistic way and that this organisation increases yeast resistance to micafungin.

An In Vitro Model for Candida albicans⁻Streptococcus gordonii Biofilms on Titanium Surfaces

The oral cavity serves as a nutrient-rich haven for over 600 species of microorganisms. Although many are essential to maintaining the oral microbiota, some can cause oral infections such as caries, periodontitis, mucositis, and endodontic infections, and this is further exacerbated with dental implants. Most of these infections are mixed species in nature and associated with a biofilm mode of growth. Here, after optimization of different parameters including cell density, growth media, and incubation conditions, we have developed an in vitro model of C. albicans–S. gordonii mixed-species biofilms on titanium discs that is relevant to infections of peri-implant diseases. Our results indicate a synergistic effect for the development of biofilms when both microorganisms were seeded together, confirming the existence of beneficial, mutualistic cross-kingdom interactions for biofilm formation. The morphological and architectural features of these dual-species biofilms formed on titanium were determined using scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Mixed biofilms formed on titanium discs showed a high level of resistance to combination therapy with antifungal and antibacterial drugs. This model can serve as a platform for further analyses of complex fungal/bacterial biofilms and can also be applied to screening of new drug candidates against mixed-species biofilms.

A phenylthiazole derivative demonstrates efficacy on treatment of the cryptococcosis & candidiasis in animal models

Aim:

In this work we test 2-(2-(cyclohexylmethylene)hydrazinyl)-4-phenylthiazole (CHT) against Cryptococcus spp. and Candida albicans.

Methods:

The ability of CHT to act in biofilm and also to interfere with C. albicans adhesion was evaluated, as well as the efficiency of the CHT in cryptococcosis and candidiasis invertebrate and murine models.

Results & conclusion:

In the present work we verified that CHT is found to inhibit Cryptococcus and C. albicans affecting biofilm in both and inhibited adhesion of Candida to human buccal cells. When we evaluated in vivo, CHT prolonged survival of Galleria mellonella after infections with Cryptococcusgattii, Cryptococcusneoformans or C. albicans and promoted a reduction in the fungal burden to the organs in the murine models. These results demonstrate CHT therapeutic potential.

Candida spp. and Cryptococcus spp. cause thousands of deaths each year. In general, antifungal drugs have several limitations to their use, and there are a limited number of these drugs available to be used in the treatments of fungal diseases. This work contributes to the search for new antifungal drugs for the treatment of candidiasis and cryptococcosis, aiming in the future, after all necessary tests, to serve as a basis for the production of drugs that could be used in the treatment of patients with these fungal diseases.

Bacterial-derived exopolysaccharides enhance antifungal drug tolerance in a cross-kingdom oral biofilm

Fungal-bacterial interactions generate unique biofilms that cause many infections in humans. Candida albicans interact with Streptococcus mutans in dental biofilms associated with severe childhood tooth-decay, a prevalent pediatric oral disease. Current modalities are ineffective and primarily based on antimicrobial monotherapies despite the polymicrobial nature of the infection. Here, we show that the combination of clinically used topical antifungal fluconazole with povidone iodine (PI) can completely suppress C. albicans carriage and mixed-biofilm formation without increasing bacterial killing activity in vivo. We unexpectedly found that the inclusion of PI enhanced fluconazole efficacy by potently disrupting the assembly of a protective bacterial exopolysaccharide (EPS) matrix through inhibition of α-glucan synthesis by S. mutans exoenzyme (GtfB) bound on the fungal surface. Further analyses revealed that the EPS produced in situ directly bind and sequester fluconazole, reducing uptake and intracellular transportation of the drug. Conversely, inhibition of GtfB activity by PI, enzymatic degradation of the α-glucan matrix or co-culturing with gtfB-defective S. mutans re-established antifungal susceptibility. Hence, topical antifungal has limitations in mixed oral biofilms due to enhanced C. albicans tolerance to fluconazole afforded by the shielding effect of bacterial-derived EPS. The data provide new insights for treatment of C. albicans in cross-kingdom biofilms, indicating that EPS inhibitors may be required for enhanced killing efficacy and optimal anti-biofilm activity.

An in vitro model of Fusobacterium nucleatum and Porphyromonas gingivalis in single- and dual-species biofilms

Purpose

The goal of this study was to develop and validate a standardized in vitro pathogenic biofilm attached onto saliva-coated surfaces.

Methods

Fusobacterium nucleatum (F. nucleatum) and Porphyromonas gingivalis (P. gingivalis) strains were grown under anaerobic conditions as single species and in dual-species cultures. Initially, the bacterial biomass was evaluated at 24 and 48 hours to determine the optimal timing for the adhesion phase onto saliva-coated polystyrene surfaces. Thereafter, biofilm development was assessed over time by crystal violet staining and scanning electron microscopy.

Results

The data showed no significant difference in the overall biomass after 48 hours for P. gingivalis in single- and dual-species conditions. After adhesion, P. gingivalis in single- and dual-species biofilms accumulated a substantially higher biomass after 7 days of incubation than after 3 days, but no significant difference was found between 5 and 7 days. Although the biomass of the F. nucleatum biofilm was higher at 3 days, no difference was found at 3, 5, or 7 days of incubation.

Conclusions

Polystyrene substrates from well plates work as a standard surface and provide reproducible results for in vitro biofilm models. Our biofilm model could serve as a reference point for studies investigating biofilms on different surfaces.

Gaining Insights from Candida Biofilm Heterogeneity: One Size Does Not Fit All

Despite their clinical significance and substantial human health burden, fungal infections remain relatively under-appreciated. The widespread overuse of antibiotics and the increasing requirement for indwelling medical devices provides an opportunistic potential for the overgrowth and colonization of pathogenic Candida species on both biological and inert substrates. Indeed, it is now widely recognized that biofilms are a highly important part of their virulence repertoire. Candida albicans is regarded as the primary fungal biofilm forming species, yet there is also increasing interest and growing body of evidence for non-Candida albicans species (NCAS) biofilms, and interkingdom biofilm interactions. C. albicans biofilms are heterogeneous structures by definition, existing as three-dimensional populations of yeast, pseudo-hyphae, and hyphae, embedded within a self-produced extracellular matrix. Classical molecular approaches, driven by extensive studies of laboratory strains and mutants, have enhanced our knowledge and understanding of how these complex communities develop, thrive, and cause host-mediated damage. Yet our clinical observations tell a different story, with differential patient responses potentially due to inherent biological heterogeneity from specific clinical isolates associated with their infections. This review explores some of the recent advances made in an attempt to explore the importance of working with clinical isolates, and what this has taught us.