Cross-feeding and interkingdom communication in dual-species biofilms of Streptococcus mutans and Candida albicans

Insights into the Cultured Bacterial Fraction of Corals

Bacteria associated with coral hosts are diverse and abundant, with recent studies suggesting involvement of these symbionts in host resilience to anthropogenic stress. Despite their putative importance, the work dedicated to culturing coral-associated bacteria has received little attention. Combining published and unpublished data, here we report a comprehensive overview of the diversity and function of culturable bacteria isolated from corals originating from tropical, temperate, and cold-water habitats. A total of 3,055 isolates from 52 studies were considered by our metasurvey. Of these, 1,045 had full-length 16S rRNA gene sequences, spanning 138 formally described and 12 putatively novel bacterial genera across the Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria phyla. We performed comparative genomic analysis using the available genomes of 74 strains and identified potential signatures of beneficial bacterium-coral symbioses among the strains. Our analysis revealed >400 biosynthetic gene clusters that underlie the biosynthesis of antioxidant, antimicrobial, cytotoxic, and other secondary metabolites. Moreover, we uncovered genomic features-not previously described for coral-bacterium symbioses-potentially involved in host colonization and host-symbiont recognition, antiviral defense mechanisms, and/or integrated metabolic interactions, which we suggest as novel targets for the screening of coral probiotics. Our results highlight the importance of bacterial cultures to elucidate coral holobiont functioning and guide the selection of probiotic candidates to promote coral resilience and improve holistic and customized reef restoration and rehabilitation efforts. IMPORTANCE Our paper is the first study to synthesize currently available but decentralized data of cultured microbes associated with corals. We were able to collate 3,055 isolates across a number of published studies and unpublished collections from various laboratories and researchers around the world. This equated to 1,045 individual isolates which had full-length 16S rRNA gene sequences, after filtering of the original 3,055. We also explored which of these had genomes available. Originally, only 36 were available, and as part of this study, we added a further 38-equating to 74 in total. From this, we investigated potential genetic signatures that may facilitate a host-associated lifestyle. Further, such a resource is an important step in the selection of probiotic candidates, which are being investigated for promoting coral resilience and potentially applied as a novel strategy in reef restoration and rehabilitation efforts. In the spirit of open access, we have ensured this collection is available to the wider research community through the web site http://isolates.reefgenomics.org/ with the hope many scientists across the globe will ask for access to these cultures for future studies.

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.

The impact of the Fungus-Host-Microbiota interplay upon Candida albicans infections: current knowledge and new perspectives

Candida albicans is a major fungal pathogen of humans. It exists as a commensal in the oral cavity, gut or genital tract of most individuals, constrained by the local microbiota, epithelial barriers and immune defences. Their perturbation can lead to fungal outgrowth and the development of mucosal infections such as oropharyngeal or vulvovaginal candidiasis, and patients with compromised immunity are susceptible to life-threatening systemic infections. The importance of the interplay between fungus, host and microbiota in driving the transition from C. albicans commensalism to pathogenicity is widely appreciated. However, the complexity of these interactions, and the significant impact of fungal, host and microbiota variability upon disease severity and outcome, are less well understood. Therefore, we summarise the features of the fungus that promote infection, and how genetic variation between clinical isolates influences pathogenicity. We discuss antifungal immunity, how this differs between mucosae, and how individual variation influences a person's susceptibility to infection. Also, we describe factors that influence the composition of gut, oral and vaginal microbiotas, and how these affect fungal colonisation and antifungal immunity. We argue that a detailed understanding of these variables, which underlie fungal-host-microbiota interactions, will present opportunities for directed antifungal therapies that benefit vulnerable patients.

Microbicidal effect of 405-nm blue LED light on Candida albicans and Streptococcus mutans dual-species biofilms on denture base resin

This study investigated: (1) the microbicidal effect of 405-nm blue LED light irradiation on biofilm formed by Candida albicans hyphae and Streptococcus mutans under dual-species condition on denture base resin, (2) the generation of intracellular reactive oxygen species (ROS) induced by irradiation, and (3) the existence of intracellular porphyrins, which act as a photosensitizer. Denture base resin specimens were prepared and C. albicans and S. mutans dual-species biofilms were allowed to form on the specimens. The biofilms were irradiated with 405-nm blue LED light and analyzed using the colony-forming unit assay, fluorescence microscopy, and scanning electron microscopy (SEM). Single-species biofilms of C. albicans and S. mutans formed on the specimens were irradiated with 405-nm blue LED light. After the irradiation, the intracellular ROS levels in C. albicans and S. mutans cells were measured. In addition, the level of intracellular porphyrins in C. albicans and S. mutans were measured. Irradiation for more than 30 min significantly inhibited the colony formation ability of C. albicans and S. mutans. Fluorescence microscopy revealed that almost all C. albicans and S. mutans cells were killed by irradiation. SEM images showed various cell damage patterns. Irradiation led to the generation of intracellular ROS and porphyrins were present in both C. albicans and S. mutans cells. In conclusion, irradiation with 405-nm blue light-emitting diode light for 40 min effectively disinfect C. albicans hyphae and S. mutans dual-species biofilms and possibly react with intracellular porphyrins resulting in generation of ROS in each microorganism.

Effect of LongZhang Gargle on Dual-Species Biofilm of Candida albicans and Streptococcus mutans

Bioactive natural products have become a hot spot for oral disease treatments. At the present study, LongZhang Gargle was investigated for its effects on single-species biofilms of Candida albicans and dual-species biofilms of Candida albicans and Streptococcus mutans. Two different models of single and dual-species biofilms were grown in YNBB medium under appropriate conditions. Biofilm biomass, biofilm architecture, and cell activity in biofilms were assessed using Crystal Violet Staining, MTT, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM). Significant reductions of biofilm biomass and fungus activity were obtained when treated with LongZhang Gargle at 2% (P < 0.05), 4% (P < 0.05), and 8% (P < 0.05) in single-species biofilms of C. albicans, and at 4% (P < 0.05) and 8% (P < 0.05) in double-species biofilms. Suppression of density, thickness, and the proportion of hyphae and fungal spores were obtained under SEM and CLSM. In conclusion, LongZhang Gargle affects single and dual-species biofilms by inhibiting biofilm biomass, cell activity, and formation of hyphae, but it does not affect the production of Extracellular polysaccharides (EPS). We speculate that LongZhang Gargle would be a promising natural drug, which can be used in treatment against C. albicans and S. mutans in oral diseases.

The architecture of a mixed fungal-bacterial biofilm is modulated by quorum-sensing signals

Interkingdom communication is of particular relevance in polymicrobial biofilms. In this work, the ability of the fungus Ophiostoma piceae to form biofilms individually and in consortium with the bacterium Pseudomonas putida, as well as the effect of fungal and bacterial signal molecules on the architecture of the biofilms was evaluated. Pseudomonas putida KT2440 is able to form biofilms through the secretion of exopolysaccharides and two large extracellular adhesion proteins, LapA and LapF. It has two intercellular signalling systems, one mediated by dodecanoic acid and an orphan LuxR receptor that could participate in the response to AHL-type quorum sensing molecules (QSMs). Furthermore, the dimorphic fungus O. piceae uses farnesol as QSM to control its yeast to hyphae morphological transition. Results show for the first time the ability of this fungus to form biofilms alone and in mixed cultures with the bacterium. Biofilms were induced by bacterial and fungal QSMs. The essential role of LapA-LapF proteins in the architecture of biofilms was corroborated, LapA was induced by farnesol and dodecanol, while LapF by 3-oxo-C6-HSL and 3-oxo-C12-HSL. Our results indicate that fungal signals can induce a transient rise in the levels of the secondary messenger c-di-GMP, which control biofilm formation and architecture.

Candida albicans promotes tooth decay by inducing oral microbial dysbiosis

Candida albicans has been detected in root carious lesions. The current study aimed to explore the action of this fungal species on the microbial ecology and the pathogenesis of root caries. Here, by analyzing C. albicans in supragingival dental plaque collected from root carious lesions and sound root surfaces of root-caries subjects as well as caries-free individuals, we observed significantly increased colonization of C. albicans in root carious lesions. Further in vitro and animal studies showed that C. albicans colonization increased the cariogenicity of oral biofilm by altering its microbial ecology, leading to a polymicrobial biofilm with enhanced acidogenicity, and consequently exacerbated tooth demineralization and carious lesion severity. More importantly, we demonstrated that the cariogenicity-promoting activity of C. albicans was dependent on PHR2. Deletion of PHR2 restored microbial equilibrium and led to a less cariogenic biofilm as demonstrated by in vitro artificial caries model or in vivo root-caries rat model. Our data indicate the critical role of C. albicans infection in the occurrence of root caries. PHR2 is the major factor that determines the ecological impact and caries-promoting activity of C. albicans in a mixed microbial consortium.

Anticaries activity of GERM CLEAN in Streptococcus mutans and Candida albicans dual-species biofilm

OBJECTIVE

To evaluate the antimicrobial effects of a peptide containing novel oral spray GERM CLEAN on dual-species biofilm formed by Streptococcus mutans and Candida albicans and to investigate whether GERM CLEAN inhibits the demineralization procedure of bovine enamel in vitro.

METHODS

The antimicrobial effects of GERM CLEAN on dual-species biofilm were analyzed by initial adherence rate calculation, water-insoluble exopolysaccharides quantification, total biomass quantification, and colony-forming units (CFUs) counting. Scanning electron microscopy and confocal laser scanning microscopy were applied to evaluate the impacts of GERM CLEAN on the biofilm structure. Further, the effects of GERM CLEAN on acidogenicity of dual-species were appraised via glycolytic pH drop analysis and hydroxyapatite dissolution measurement. The percentage of Surface Microhardness Reduction (%SMHR) evaluation, Atomic Force Micrograph (AFM) examination, and Transverse Microradiography (TMR) analysis after pH cycling were used to determine whether GERM CLEAN inhibited the demineralization of bovine enamel.

RESULTS

GERM CLEAN decreased the adherence rate, water-insoluble EPS production, biofilm formation, and acidogenicity of the dual-species. Moreover, GERM CLEAN significantly inhibited the demineralization status of bovine enamels.

CONCLUSION

This peptide containing novel oral spray GERM CLEAN has antimicrobial potential toward the dual-species. GERM CLEAN can also impede the demineralization procedure of enamel.

Chemical signals driving bacterial-fungal interactions

Microorganisms reside in diverse environmental communities where interactions become indispensable due to close physical associations. These interactions are driven by chemical communication among different microbial kingdoms, particularly between fungi and bacteria. Knowledge about these communication signals provides useful information about the nature of microbial interactions and allows predictions of community development in diverse environments. Here, we provide an update on the role of small signalling molecules in fungal-bacterial interactions with focus on agricultural and medicinal environments. This review highlights the range of - and response to - diverse biochemicals produced by both kingdoms with view to harnessing their properties towards drug discovery applications.

Oral Mycobiome Differences in Various Spatial Niches With and Without Severe Early Childhood Caries

Purpose: Severe early childhood caries (S-ECC) is a microbe-mediated disease with tooth hard tissue destruction. However, the role of the fungal community in various ecological niches of deciduous dental caries has not been fully elucidated. This study aimed to analyze the differences of mycobiome in diverse spatial niches with and without S-ECC. Method: A total of 48 samples were obtained from 8 S-ECC children (SE group) and 8 caries-free children (CF group) aged 4-5 years. Unstimulated saliva (S), healthy supragingival plaque (FMIX), mixed plaque from decayed teeth (SMIX) and carious lesion (DMIX) samples were collected. The ITS2 region of the fungi was amplified and sequenced using the Ion S5™XL platform. Results: A total of 281 species were identified. Candida albicans showed relatively higher abundance in S-ECC children, while Alternaria alternata and Bipolaris sorokiniana were more enriched in CF group. In this study, the relative abundance of C. albicans in CF.FMIX (0.4%), SE.FMIX (12.5%), SE.SMIX (24.0%), and SE.DMIX (37.2%) increased successively. Significant differences of fungal species richness and diversity were observed between SE.FMIX-SE.SMIX, SE.FMIX-SE.DMIX (P < 0.05). Conclusions: The diversity of fungal communities in S-ECC children showed significant differences in various spatial niches of primary teeth. The richness of C. albicans was closely related to the caries states and depth, suggesting that it may play a crucial role in caries pathogenicity.

Omics and interspecies interaction

Interspecies interactions are key determinants in biofilm behavior, ecology, and architecture. The cellular responses of microorganisms to each other at transcriptional, proteomic, and metabolomic levels ultimately determine the characteristics of biofilm and the corresponding implications for health and disease. Advances in omics technologies have revolutionized our understanding of microbial community composition and their activities as a whole. Large-scale analyses of the complex interaction between the many microbial species residing within a biofilm, however, are currently still hampered by technical and bioinformatics challenges. Thus, studies of interspecies interactions have largely focused on the transcriptional and proteomic changes that occur during the contact of a few prominent species, such as Porphyromonas gingivalis, Streptococcus mutans, Candida albicans, and a few others, with selected partner species. Expansion of available tools is necessary to grow the revealing, albeit limited, insight these studies have provided into a profound understanding of the nature of individual microbial responses to the presence of others. This will allow us to answer important questions including: Which intermicrobial interactions orchestrate the myriad of cooperative, synergistic, antagonistic, manipulative, and other types of relationships and activities in the complex biofilm environment, and what are the implications for oral health and disease?

Increased Intraspecies Diversity in Escherichia coli Biofilms Promotes Cellular Growth at the Expense of Matrix Production

Intraspecies diversity in biofilm communities is associated with enhanced survival and growth of the individual biofilm populations. Studies on the subject are scarce, namely, when more than three strains are present. Hence, in this study, the influence of intraspecies diversity in biofilm populations composed of up to six different Escherichia coli strains isolated from urine was evaluated in conditions mimicking the ones observed in urinary tract infections and catheter-associated urinary tract infections. In general, with the increasing number of strains in a biofilm, an increase in cell cultivability and a decrease in matrix production were observed. For instance, single-strain biofilms produced an average of 73.1 µg·cm⁻² of extracellular polymeric substances (EPS), while six strains biofilms produced 19.9 µg·cm⁻². Hence, it appears that increased genotypic diversity in a biofilm leads E. coli to direct energy towards the production of its offspring, in detriment of the production of public goods (i.e., matrix components). Apart from ecological implications, these results can be explored as another strategy to reduce the biofilm burden, as a decrease in EPS matrix production may render these intraspecies biofilms more sensitive to antimicrobial agents.

Disruption of Streptococcus mutans and Candida albicans synergy by a commensal streptococcus

Polymicrobial interactions in dental plaque play a significant role in dysbiosis and homeostasis in the oral cavity. In early childhood caries, Streptococcus mutans and Candida albicans are often co-isolated from carious lesions and associated with increased disease severity. Studies have demonstrated that metabolic and glucan-dependent synergism between C. albicans and S. mutans contribute to enhanced pathogenesis. However, it is unclear how oral commensals influence pathogen synergy. Streptococcus parasanguinis, a hydrogen peroxide (H2O2) producing oral commensal, has antimicrobial activity against S. mutans. In this study, we utilized a three species biofilm model to understand the impact of S. parasanguinis on S. mutans and C. albicans synergy. We report that S. parasanguinis disrupts S. mutans and C. albicans biofilm synergy in a contact and H2O2-independent manner. Further, metabolomics analysis revealed a S. parasanguinis-driven alteration in sugar metabolism that restricts biofilm development by S. mutans. Moreover, S. parasanguinis inhibits S. mutans glucosyltransferase (GtfB) activity, which is important for glucan matrix development and GtfB-mediated binding to C. albicans mannan. Taken together, our study describes a new antimicrobial role for S. parasanguinis and highlights how this abundant oral commensal may be utilized to attenuate pathogen synergism.

Synergistic interaction of eugenol and antimicrobial drugs in eradication of single and mixed biofilms of Candida albicans and Streptococcus mutans

In vitro eradication of the C. albicans and S. mutans mixed biofilms by eugenol alone and in combination with the antimicrobial drugs. Previously characterized strains of C. albicans (CAJ-01 and CAJ-12) and S. mutans MTCC497 were used to evaluate the eradication of biofilms using XTT reduction assay, viability assay, time dependent killing assay and scanning electron microscopy (SEM). Synergistic interaction was assessed by checkerboard method. Sessile MIC (SMIC) of eugenol was equivalent to the planktonic MIC (PMIC) against C. albicans and S. mutans mixed biofilms. SMIC of fluconazole and azithromycin was increased upto 1000-folds over PMIC. Eradication of single or mixed biofilms was evident from the viability assay and SEM. At 1 × MIC of eugenol, log10CFU count of C. albicans cells were decreased from 6.3 to 4.2 and 3.8 (p < 0.05) in single and mixed biofilms, respectively. SEM studies revealed the eradication of C. albicans and S. mutans cells from glass surface at 800 µg/mL concentration of eugenol. Time dependent killing assay showed dose dependent effect of eugenol on pre-formed CAJ-01, CAJ-12 and S. mutans biofilm cells. Eugenol was highly synergistic with fluconazole (FICI = 0.156) against CAJ-12 single biofilms. However, the combination of eugenol and azithromycin showed maximum synergy (FICI = 0.140) against pre-formed C. albicans and S. mutans mixed biofilms. These findings highlighted the promising efficacy of eugenol in the eradication of biofilms of two oral pathogens (C. albicans and S. mutans) in vitro and could also be exploited in synergy with fluconazole and azithromycin in controlling oral infections.

Deciphering the succession dynamics of dominant and rare genera in biofilm development process

Deciphering the succession dynamics of dominant and rare taxa is crucial to understand the stability and ecosystem functions of biofilm communities. However, the essential laws of the succession dynamics based on dominant and rare taxa were still unenlightened. Herein, we investigated the succession dynamics of dominant and rare genera in multi-species biofilms developed in flow cells fed with 10 and 40 mg-TOC/L LB broth. The relative abundance of dominant genera (Enterobacteria and Acinetobacter) decreased remarkably (from 94.63% to 73.22%) in 10 mg-TOC/L LB broth, whereas they kept relatively steady (93.75 ± 4.23%) along with the cultivation time in 40 mg-TOC/L LB broth. Fluorescence in situ hybridization showed that rare genera tended to form clusters at both concentrations, while weaker dispersal of dominant genera caused patchier biofilm structures in 10 mg-TOC/L LB broth compared to that in 40 mg-TOC/L LB broth. Null model analyses further demonstrated that the stochastic ecological drift was more pronounced in the community assembly of biofilms in 10 mg-TOC/L LB broth (73.33%) than those in 40 mg-TOC/L LB broth (60.95%), weakening the competitive superiority of dominant taxa in the patchier biofilms. In addition, the co-occurrence network reflected that the positive interactions among rare genera contributed to exclude dominant genera in 10 mg-TOC/L LB broth, whereas negative interactions only occurred between the dominant Enterobacter and Acinetobacter or rare Comamonas in 40 mg-TOC/L LB broth. This study highlighted the distinctive succession dynamics of dominant and rare genera in biofilms at different substrate concentrations, which would advance our understanding of the biofilm communities in biofilm-related process.

Dynamics of Mono- and Dual-Species Biofilm Formation and Interactions Between Paracoccidioides brasiliensis and Candida albicans

The oral cavity is a highly diverse microbial environment in which microorganisms interact with each other, growing as biofilms on biotic and abiotic surfaces. Understanding the interaction among oral microbiota counterparts is pivotal for clarifying the pathogenesis of oral diseases. Candida spp. is one of the most abundant fungi in the oral mycobiome with the ability to cause severe soft tissue lesions under certain conditions. Paracoccidioides spp., the causative agent of paracoccidioidomycosis, may also colonize the oral cavity leading to soft tissue damage. It was hypothesized that both fungi can interact with each other, increasing the growth of the biofilm and its virulence, which in turn can lead to a more aggressive infectivity. Therefore, this study aimed to evaluate the dynamics of mono- and dual-species biofilm growth of Paracoccidioides brasiliensis and Candida albicans and their infectivity using the Galleria mellonella model. Biomass and fungi metabolic activity were determined by the crystal violet and the tetrazolium salt reduction tests (XTT), respectively, and the colony-forming unit (CFU) was obtained by plating. Biofilm structure was characterized by both scanning electronic- and confocal laser scanning- microscopy techniques. Survival analysis of G. mellonella was evaluated to assess infectivity. Our results showed that dual-species biofilm with P. brasiliensis plus C. albicans presented a higher biomass, higher metabolic activity and CFU than their mono-species biofilms. Furthermore, G. mellonella larvae infected with P. brasiliensis plus C. albicans presented a decrease in the survival rate compared to those infected with P. brasiliensis or C. albicans, mainly in the form of biofilms. Our data indicate that P. brasiliensis and C. albicans co-existence is likely to occur on oral mucosal biofilms, as per in vitro and in vivo analysis. These data further widen the knowledge associated with the dynamics of fungal biofilm growth that can potentially lead to the discovery of new therapeutic strategies for these infections.

Rich Repertoire of Quorum Sensing Protein Coding Sequences in CPR and DPANN Associated with Interspecies and Interkingdom Communication

The selection of predicted genes for interspecies communication within the CPR and DPANN genomes sheds some light onto the underlying mechanisms supporting their inferred symbiotic lifestyle. Also, considering the lack of core pathways such as the de novo synthesis of nucleotides or amino acids in the CPR and DPANN lineages, the persistence of these genes highlights how determinant social traits can be for the survival of some microorganisms. Finally, the considerable number of variants of QS proteins identified among the 69 CPR and DPANN phyla substantially expands our knowledge of prokaryotic communication across the tree of life and suggests that the multiplicity of “dialects” in the microbial world is probably larger than previously appreciated.

The bacterial candidate phyla radiation (CPR) and the archaeal DPANN superphylum are two novel lineages that have substantially expanded the tree of life due to their large phylogenetic diversity. Because of their ultrasmall size, reduced genome, and lack of core biosynthetic capabilities, most CPR and DPANN members are predicted to be sustained through their interactions with other species. How the few characterized CPR and DPANN symbionts achieve these critical interactions is, however, poorly understood. Here, we conducted an in silico analysis on 2,597 CPR/DPANN genomes to test whether these ultrasmall microorganisms might encode homologs of reference proteins involved in the synthesis and/or the detection of 26 different types of communication molecules (quorum sensing [QS] signals), since QS signals are well-known mediators of intra- and interorganismic relationships. We report the discovery of 5,693 variants of QS proteins distributed across 63 CPR and 6 DPANN phyla and associated with 14 distinct types of communication molecules, most of which were characterized as interspecies QS signals.

IMPORTANCE The selection of predicted genes for interspecies communication within the CPR and DPANN genomes sheds some light onto the underlying mechanisms supporting their inferred symbiotic lifestyle. Also, considering the lack of core pathways such as the de novo synthesis of nucleotides or amino acids in the CPR and DPANN lineages, the persistence of these genes highlights how determinant social traits can be for the survival of some microorganisms. Finally, the considerable number of variants of QS proteins identified among the 69 CPR and DPANN phyla substantially expands our knowledge of prokaryotic communication across the tree of life and suggests that the multiplicity of “dialects” in the microbial world is probably larger than previously appreciated.

The initial inoculation ratio regulates bacterial coculture interactions and metabolic capacity

Coculture is an important model system in microbial ecology studies. As a key experimental parameter, the initial inoculation ratio has a crucial impact on the results of the coculture system. However, such an effect has never been investigated under multiple niche conditions. In this study, we established a simple coculture system with two model bacteria in various carbon sources and investigated the influence of initial inoculum ratios of 1:1000 to 1000:1 on community structure, function, and bacterial interaction. We found that the final ratio of the cocultures with different initial inoculum ratios differed in approximately five-sixths of the carbon sources, suggesting that the final ratio is highly dependent on the initial inoculum ratio, while the carbon source preferences of bacteria could not predict the final ratio of cocultures. Furthermore, we found that the initial ratio could regulate the metabolic capacity of the coculture, as only cocultures with initial ratios of 1:1 and 1000:1 gained high capacity on 14 specific carbon sources. The underlying reason may be that the pattern of species interaction is changed by the initial ratio. In conclusion, we showed that the initial ratio can induce emergent properties in coculture. These findings suggest that the initial ratio not only impacts the reproducibility of coculture experiments but also can influence our understanding of generic microbial ecology.

A Two-Way Road: Antagonistic Interaction Between Dual-Species Biofilms Formed by Candida albicans/Candida parapsilosis and Trichophyton rubrum

Dermatomycoses include superficial fungal infections of the skin and its appendages. Trichophyton rubrum, Candida albicans, and Candida parapsilosis are some of the most prevalent species that cause dermatomycoses. Several studies show a variable predominance of Candida spp. in relation to dermatophytes, especially in onychomycosis and the possibility of isolating both from the same site. The ability of dermatophytes to form biofilms recently been explored and there is currently no evidence on the involvement of these filamentous fungi in multi-species biofilms. Thus, this study aims to investigate the probable dual-species interaction between T. rubrum and C. albicans and T. rubrum and C. parapsilosis biofilms, considering variable formation conditions, as well as the susceptibility of these dual-species biofilms against terbinafine and efinaconazole. Three conditions of formation of dual-species biofilms were tested: (a) the suspensions of T. rubrum and Candida albicans or C. parapsilosis placed together; (b) suspensions of C. albicans and C. parapsilosis added the pre-adhesion of T. rubrum biofilms; (c) after the maturation of T. rubrum sessile cells. In the first and second conditions, the quantification of metabolic activities, biomass, and polysaccharide materials of mixed biofilms tended to resemble Candida monospecies biofilms. In the third condition, the profiles were modified after the addition of Candida, suggesting that T. rubrum biofilms served as substrate for the development of Candida biofilms. Scanning electron microscopy showed Candida predominance, however, numerous blastoconidia were noted, most evident in the conditions under which Candida was added after the pre-adhesion and maturation of T. rubrum biofilms. Despite the predominance of Candida, the presence of T. rubrum appears to inhibit C. albicans filamentation and C. parapsilosis development, confirming an antagonistic interaction. Fungal burden assays performed when the biofilms were formed together confirmed Candida predominance, as well as susceptibility to antifungals. Further studies will be needed to identify the components of the Candida and T. rubrum biofilm supernatants responsible for inhibiting dermatophyte growth and C. albicans filamentation.

Effect of bioactive compounds on the regulation of quorum sensing network-associated genes and virulence in Streptococcus mutans-A systematic review

OBJECTIVE

The aim of this study was to systematically review the literature on the effect of bioactive compounds and their regulation of quorum sensing (QS)-related and/or -regulated-virulence genes expression in Streptococcus mutans.

DESIGN

The search strategy was conducted through the electronic databases Pubmed, Scopus, and Web of Science for studies reporting the effects of natural and synthetic bioactive compounds on the regulation of QS-associated and/or -regulated genes of S. mutans.

RESULTS

After full-text reading, 19 studies met the inclusion criteria, in most of them, QS-inhibitors from synthetic origin were evaluated, 16 articles described the effect of the compounds on biofilm formation cultivated in vitro and five studies described these effects on adhesion of biofilm-producing cells. Only 2 studies analyzed the potential target-component of the QS.

CONCLUSIONS

Mostly, the bioactive compounds affected the expression of QS-associated and/or -regulated genes and virulence traits (e.g. adhesion, biofilm formation, acid stress tolerance) of S. mutans. Further studies are necessary to elucidate the target-specific QS-system constituent used by bioactive compounds to achieve QS inhibition as well as validate the use of these compounds in controlling dental caries.

Effect of cell-free spent media prepared from Aggregatibacter actinomycetemcomitans on the growth of Candida albicans and Streptococcus mutans in co-species biofilms

This study explored the influence of cell-free spent media prepared from Aggregatibacter actinomycetemcomitans LuxS mutant (Aa-LuxS), its wild type strain (Aa-WT), and the laboratory strain (Aa-Y4), on the interaction between Candida albicans and Streptococcus mutans while growing in co-species biofilm for 48 h. By analyzing the results of crystal violet staining, [3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide] (MTT) assays, and quantitative real-time polymerase chain reaction (qPCR), we found that the presence of Aa-LuxS in treated biofilms did not affect biofilm development, while added Aa-WT or Aa-Y4 resulted in a significant decrease in both biofilm mass and the number of cells. The inhibitory effect of Aa-WT or Aa-Y4 was not dependent on the protein concentration in the spent media tested (1 and 10%). Gene transcription analyses indicated that Aa-WT/Aa-Y4 exhibits comparable inhibitory effects on the expression of hyphal-associated genes (ALS3 and HWP1), but not on the expression of YWP1, which encodes a yeast form of C. albicans. In contrast, except for gtfD, the expression of S. mutans gtfB/C genes encoding glucosyltransferase was not affected in Aa-WT and Aa-Y4 treated biofilms compared to the levels found in Aa-LuxS treated biofilms. Our results indicate that AI-2-containing spent media derived from Aa can reduce biofilm biomass without significantly inhibiting the survival rate of S. mutans.

Candida and dental caries in children, adolescents and adults: A systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aimed to investigate whether the presence of fungi of the genus Candida in oral cavity is associated with dental caries in children and adolescents (from 6 to 18 years) or in adults (older than 18 years).

DESIGN

Electronic search was carried out in MEDLINE, EMBASE and LILACS databases. Studies that evaluated the presence of Candida spp. and dental caries on those individuals were included. Data extraction and evidence quality assessment were performed by two independent investigators. Prevalence ratio (PR) was calculated considering 95 % confidence interval (CI). Meta-analysis was performed using random effect Mantel-Haenszel model.

RESULTS

Thirty out of 123 publications selected for full-reading were included in the systematic review. Prevalence of Candida spp. in the oral cavity ranged from 7.7 % to 78 %. Prevalence of dental caries in individuals harbouring Candida spp. ranged from 27.2%-100% and was higher than in individuals not harbouring Candida spp. (PR = 1.72 [1.46-2.02]). Prevalence of dental caries was 2.3 times higher in individuals harbouring Candida spp. in mucosa. Moreover, dental caries prevalence was 80 % and 48 % higher in children/adolescents and adults harbouring Candida spp., respectively (95 % CI [1.44-2.25] and [1.20-1.83]). The quality of evidence of most studies (n = 21) was graded as fair.

CONCLUSIONS

These results suggest that, regardless of age or sample site, individuals with the presence of Candida spp. have a higher prevalence of dental caries when compared to individuals without these microorganisms in the oral cavity.

Does the Gut Microbiota Modulate Host Physiology through Polymicrobial Biofilms?

Microbes inhabit various environments, such as soil, water environments, plants, and animals. Humans harbor a complex commensal microbial community in the gastrointestinal tract, which is known as the gut microbiota. The gut microbiota participates not only in various metabolic processes in the human body, it also plays a critical role in host immune responses. Gut microbes that inhabit the intestinal epithelial surface form polymicrobial biofilms. In the last decade, it has been widely reported that gut microbial biofilms and gut microbiota-derived products, such as metabolites and bacterial membrane vesicles, not only directly affect the host intestinal environment, but also indirectly influence the health of the host. In this review, we discuss the most recent findings from human and animal studies on the interactions between the gut microbiota and hosts, and their associations with various disorders, including inflammatory diseases, atopic dermatitis, metabolic disorders, and psychiatric and neurological diseases. The integrated approach of metabologenomics together with biofilm imaging may provide valuable insights into the gut microbiota and suggest remedies that may lead to a healthier society.

Cajuputs candy impairs Candida albicans and Streptococcus mutans mixed biofilm formation in vitro

Background: Cajuputs candy (CC), an Indonesian functional food, utilizes the bioactivity of Melaleuca cajuputi essential oil (MCEO) to maintain oral cavity health. Synergistic interaction between Candida albicans and Streptococcus mutans is a crucial step in the pathogenesis of early childhood caries. Our recent study revealed several alternative MCEOs as the main flavors in CC. The capacity of CC to interfere with the fungus-bacterium relationship remains unknown. This study aimed to evaluate CC efficacy to impair biofilm formation by these dual cariogenic microbes.

Methods: The inhibition capacity of CC against mixed-biofilm comprising C. albicans and S. mutans was assessed by quantitative (crystal violet assay, tetrazolium salt [MTT] assay, colony forming unit/mL counting, biofilm-related gene expression) and qualitative analysis (light microscopy and scanning electron microscopy).

Result: Both biofilm-biomass and viable cells were significantly reduced in the presence of CC. Scanning electron microscopy imaging confirmed this inhibition capacity, demonstrating morphology alteration of C. albicans, along with reduced microcolonies of S. mutans in the biofilm mass. This finding was related to the transcription level of selected biofilm-associated genes, expressed either by C. albicans or S. mutans. Based on qPCR results, CC could interfere with the transition of C. albicans yeast form to the hyphal form, while it suppressed insoluble glucan production by S. mutans. G2 derived from Mojokerto MCEO showed the greatest inhibition activity on the relationship between these cross-kingdom oral microorganisms (p < 0.05).

Conclusion: In general, all CC formulas showed biofilm inhibition capacity. Candy derived from Mojokerto MCEO showed the greatest capacity to maintain the yeast form of C. albicans and to inhibit extracellular polysaccharide production by S. mutans. Therefore, the development of dual-species biofilms can be impaired effectively by the CC tested.

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.

Antifungal Activity of Magnesium Oxide Nanoparticles: Effect on the Growth and Key Virulence Factors of Candida albicans

The aim of this research was to study the effects of different concentrations of magnesium oxide nanoparticles (MgO NPs) on the growth and key virulence factors of Candida albicans (C. albicans). The minimum inhibitory concentration (MIC) of MgO NPs against C. albicans was determined by the micro-broth dilution method. A time-kill curve of MgO NPs and C. albicans was established to investigate the ageing effect of MgO NPs on C. albicans. Crystal violet staining, the MTT assay, and inverted fluorescence microscopy were employed to determine the effects of MgO NPs on C. albicans adhesion, two-phase morphological transformation, biofilm biomass, and metabolic activity. The time-kill curve showed that MgO NPs had fungicidal and antifungal activity against C. albicans in a time- and concentration-dependent manner. Semi-quantitative crystal violet staining and MTT assays showed that MgO NPs significantly inhibited C. albicans biofilm formation and metabolic activity, and the difference was statistically significant (p < 0.001). Inverted fluorescence microscopy showed that MgO NPs could inhibit the formation of C. albicans biofilm hyphae. Adhesion experiments showed that MgO NPs significantly inhibited the initial adhesion of C. albicans (p < 0.001). This study demonstrates that MgO NPs can effectively inhibit the growth, initial adhesion, two-phase morphological transformation, and biofilm formation of C. albicans and is an antifungal candidate.

Evaluation of antifungal activity of six children's toothpaste on Candida albicans isolated from early childhood caries patients

BACKGROUND

Early childhood caries (ECC) is an aggressive, destructive form of dental caries that affects the children younger than 6 years of age. Candida is known to increase the adherence of Streptococcus mutans to the oral biofilm and produce acids that cause tooth demineralization.

AIM OF THE STUDY

To evaluate the efficacy of six commercially available children's toothpaste on clinical isolates of Candida albicans obtained from ECC patients.

MATERIALS AND METHODS

The study population comprised 60 children aged 3-6 years having ECC. Samples were divided into six groups comprising ten children in each group. Samples were collected using sterile cotton swabs, inoculated on Sabouraud dextrose agar, and incubated at 37°C for 24 h. Species identification was done by germ tube test and growth on corn meal agar. After the confirmed growth of C. albicans, the six commercially available children's toothpaste namely Organic Children's Coconut Oil Toothpaste^®, Aloe Dent Children's Toothpaste^®, Patanjali Dant Kanti Junior Toothpaste^®, Colgate Kids Toothpaste^®, Pediflor Kids Toothpaste^®, and Crest Pro-Health Stages Kids Toothpaste^® and distilled water as control group were subjected for antifungal activity of C. albicans. Agar plates were incubated at 37°C for 48 h, and the diameter of the zones of inhibition was measured and recorded. Data were tabulated and statistical analysis was done using Statistical Package for the Social Science (16.0) version.

RESULTS

Pediflor kids toothpaste® showed maximum antifungal activity and Aloe Dent children's toothpaste® showed minimum antifungal activity.

CONCLUSION

All brands of children's toothpaste show antifungal activity against Candida albicans.

In Vivo Effects of a Hydroxyapatite-Based Oral Care Gel on the Calcium and Phosphorus Levels of Dental Plaque

OBJECTIVES

 Particulate hydroxyapatite (HAP; Ca5(PO4)3(OH)) is a biomimetic oral care ingredient. One mode of action in caries-susceptible individuals may be the adhesion/incorporation of HAP into dental plaque. Therefore, the aim of this in vivo study was to analyze the 3-day effects of a newly developed hydroxyapatite-based oral care gel on the calcium and phosphorus levels within the dental plaque of children.

MATERIALS AND METHODS

 This study was conducted in Kebon Padangan at Bali in Indonesia. Thirty-four children (mean age, 8.9 years; mean DMF-T [decayed, missing, and filled teeth; permanent teeth], 0.6; mean dmft-t [primary teeth] 4.5) were included in the study. The gel was applied thrice for 3 days by an experienced dentist. Dental plaque was collected at baseline and after the study. Levels of calcium and phosphorus of plaque samples were analyzed by energy-dispersive X-ray spectroscopy.

STATISTICAL ANALYSIS

 Medians for both calcium and phosphorus levels were calculated (baseline and 3-day application of HAP-gel).

RESULTS

 The calcium level increased after 3 days of application of the HAP-gel from 0.25 wt% (median) to 0.40 wt% (median), while the phosphorus level increased from 1.17 wt% (median) to 1.41 wt% (median). However, variations in both calcium and phosphorus levels measured in the pooled dental plaque samples were high.

CONCLUSION

 Within the limitations of the study, the 3-day application of the oral HAP-gel in children increased the median of both calcium and phosphorus levels in plaque. Consequently, a positive influence on the remineralization/demineralization process is very likely.

The Role of Candida albicans Secreted Polysaccharides in Augmenting Streptococcus mutans Adherence and Mixed Biofilm Formation: In vitro and in vivo Studies

The oral cavity is a complex environment harboring diverse microbial species that often co-exist within biofilms formed on oral surfaces. Within a biofilm, inter-species interactions can be synergistic in that the presence of one organism generates a niche for another enhancing colonization. Among these species are the opportunistic fungal pathogen Candida albicans and the bacterial species Streptococcus mutans, the etiologic agents of oral candidiasis and dental caries, respectively. Recent studies have reported enhanced prevalence of C. albicans in children with caries indicating potential clinical implications for this fungal-bacterial interaction. In this study, we aimed to specifically elucidate the role of C. albicans-derived polysaccharide biofilm matrix components in augmenting S. mutans colonization and mixed biofilm formation. Comparative evaluations of single and mixed species biofilms demonstrated significantly enhanced S. mutans retention in mixed biofilms with C. albicans. Further, S. mutans single species biofilms were enhanced upon exogenous supplementation with purified matrix material derived from C. albicans biofilms. Similarly, growth in C. albicans cell-free spent biofilm culture media enhanced S. mutans single species biofilm formation, however, the observed increase in S. mutans biofilms was significantly affected upon enzymatic digestion of polysaccharides in spent media, identifying C. albicans secreted polysaccharides as a key factor in mediating mixed biofilm formation. The enhanced S. mutans biofilms mediated by the various C. albicans effectors was also demonstrated using confocal laser scanning microscopy. Importantly, a clinically relevant mouse model of oral co-infection was adapted to demonstrate the C. albicans-mediated enhanced S. mutans colonization in a host. Analyses of harvested tissue and scanning electron microscopy demonstrated significantly higher S. mutans retention on teeth and tongues of co-infected mice compared to mice infected only with S. mutans. Collectively, the findings from this study strongly indicate that the secretion of polysacharides from C. albicans in the oral environment may impact the development of S. mutans biofilms, ultimately increasing dental caries and, therefore, Candida oral colonization should be considered as a factor in evaluating the risk of caries.

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.

Oral Candidiasis: A Disease of Opportunity

Oral candidiasis, commonly referred to as “thrush,” is an opportunistic fungal infection that commonly affects the oral mucosa. The main causative agent, Candida albicans, is a highly versatile commensal organism that is well adapted to its human host; however, changes in the host microenvironment can promote the transition from one of commensalism to pathogen. This transition is heavily reliant on an impressive repertoire of virulence factors, most notably cell surface adhesins, proteolytic enzymes, morphologic switching, and the development of drug resistance. In the oral cavity, the co-adhesion of C. albicans with bacteria is crucial for its persistence, and a wide range of synergistic interactions with various oral species were described to enhance colonization in the host. As a frequent colonizer of the oral mucosa, the host immune response in the oral cavity is oriented toward a more tolerogenic state and, therefore, local innate immune defenses play a central role in maintaining Candida in its commensal state. Specifically, in addition to preventing Candida adherence to epithelial cells, saliva is enriched with anti-candidal peptides, considered to be part of the host innate immunity. The T helper 17 (Th17)-type adaptive immune response is mainly involved in mucosal host defenses, controlling initial growth of Candida and inhibiting subsequent tissue invasion. Animal models, most notably the mouse model of oropharyngeal candidiasis and the rat model of denture stomatitis, are instrumental in our understanding of Candida virulence factors and the factors leading to host susceptibility to infections. Given the continuing rise in development of resistance to the limited number of traditional antifungal agents, novel therapeutic strategies are directed toward identifying bioactive compounds that target pathogenic mechanisms to prevent C. albicans transition from harmless commensal to pathogen.

The manifold roles of microbial ribosomal peptide-based natural products in physiology and ecology

The ribosomally synthesized and posttranslationally modified peptides (RiPPs), also called ribosomal peptide natural products (RPNPs), form a growing superfamily of natural products that are produced by many different organisms and particularly by bacteria. They are derived from precursor polypeptides whose modification by various dedicated enzymes helps to establish a vast array of chemical motifs. RiPPs have attracted much interest as a source of potential therapeutic agents, and in particular as alternatives to conventional antibiotics to address the bacterial resistance crisis. However, their ecological roles in nature are poorly understood and explored. The present review describes major RiPP actors in competition within microbial communities, the main ecological and physiological functions currently evidenced for RiPPs, and the microbial ecosystems that are the sites for these functions. We envision that the study of RiPPs may lead to discoveries of new biological functions and highlight that a better knowledge of how bacterial RiPPs mediate inter-/intraspecies and interkingdom interactions will hold promise for devising alternative strategies in antibiotic development.

[Research progress on interactions between Candida albicans and common oral pathogens]

Increasing numbers of microbiome studies have enabled the development of a greater understanding of how antagonistic and synergetic microbial interactions influence disease outcomes. Candida albicans is an opportunistic pathogen that is commonly found in human oral microflora. In a healthy oral environment, Candida albicans may potentially but sig-nificantly influence the balance between the oral bacterial ecosystem and the host, leading tooral diseases. The aim of this study is to review the correlation between Candida albicans and oral pathogens and provide a deeper understanding of the nature of oral infec-tious diseases.

Isolation and characterization of Enterococcus faecium DSM 20477 with ability to secrete antimicrobial substance for the inhibition of oral pathogen Streptococcus mutans UKMCC 1019

Streptococcus mutans and Candida albicans are the main oral pathogens which contribute to dental caries that affects all ages of human being.

OBJECTIVES

This study focuses on the potential of crude cell free supernatant (CCFS) from lactic acid bacteria (LAB) to inhibit of the growth of S. mutans UKMCC 1019.

DESIGN

A total of 61 CCFS from LAB strains were screened for their inhibitory ability against S. mutans UKMCC 1019 by broth microdilution method. The selected LAB with highest antimicrobial activity was identified and its CCFS was characterized for pH stability, temperature tolerance, enzyme sensitivity, metabolism of carbohydrates, enzymatic activities and antimicrobial activity against S. mutans UKMCC 1019 and C. albicans UKMCC 3001 by well diffusion assay. The effect of CCFS on cell structure of S. mutans UKMCC 1019 was observed under transmission electron microscopy (TEM).

RESULTS

The CCFS from isolate CC2 from Kimchi showed the highest inhibition against S. mutans UKMCC 1019, which was 76.46 % or 4406.08 mm²/mL and it was identified to be most closely related to Enterococcus faecium DSM 20477 based on 16 s rRNA sequencing. The CCFS of E. faecium DSM 20477 had high tolerance to acidic and alkaline environment as well as high temperature. It also shows high antifungal activities against C. albicans UKMCC 3001 with 2362.56 mm²/mL. Under TEM, the cell walls and the cytoplasm membrane of S. mutans UKMCC 1019 were disrupted by the antimicrobial substance, causing cell lysis.

CONCLUSIONS

Hence, the CCFS from E. faecium DSM 20477 is a potential bacteriocin in future for the treatment of dental caries.

Cajuputs candy impairs Candida albicans and Streptococcus mutans mixed biofilm formation in vitro

Background: Cajuputs candy (CC), an Indonesian functional food, utilizes the bioactivity of Melaleuca cajuputi essential oil (MCEO) to maintain oral cavity health. Synergistic interaction between Candida albicans and Streptococcus mutans is a crucial step in the pathogenesis of early childhood caries. Our recent study revealed several alternative MCEOs as the main flavors in CC. The capacity of CC to interfere with the fungus-bacterium relationship remains unknown. This study aimed to evaluate CC efficacy to impair biofilm formation by these dual cariogenic microbes. Methods: The inhibition capacity of CC against mixed-biofilm comprising C. albicans and S. mutans was assessed by quantitative (crystal violet assay, tetrazolium salt [MTT] assay, colony forming unit/mL counting, biofilm-related gene expression) and qualitative analysis (light microscopy and scanning electron microscopy). Result: Both biofilm-biomass and viable cells were significantly reduced in the presence of CC. Scanning electron microscopy imaging confirmed this inhibition capacity, demonstrating morphology alteration of C. albicans, along with reduced microcolonies of S. mutans in the biofilm mass. This finding was related to the transcription level of selected biofilm-associated genes, expressed either by C. albicans or S. mutans. Based on qPCR results, CC could interfere with the transition of C. albicans yeast form to the hyphal form, while it suppressed insoluble glucan production by S. mutans. G2 derived from Mojokerto MCEO showed the greatest inhibition activity on the relationship between these cross-kingdom oral microorganisms (p < 0.05). Conclusion: In general, all CC formulas showed biofilm inhibition capacity. Candy derived from Mojokerto MCEO showed the greatest capacity to maintain the commensal form of C. albicans and to inhibit extracellular polysaccharide production by S. mutans. Therefore, the development of dual-species biofilms can be impaired effectively by the CC tested.

Monospecies and polymicrobial biofilms differentially regulate the phenotype of genotype-specific oral cancer cells

Microbial infection has been shown to involve in oral carcinogenesis; however, the underlying mechanisms remain poorly understood. The present study aimed to characterize the growth of oral microorganisms as both monospecies and polymicrobial biofilms and determine the effects of their products on oral keratinocytes. Candida albicans (ALC3), Actinomyces naeslundii (AN) and Streptococcus mutans (SM) biofilms or a combination of these (TRI) were grown in flow-cell system for 24 h. The biofilms were subjected to fluorescent in situ hybridization using species-specific probes and analysed using confocal laser scanning microscopy. The effluent derived from each biofilm was collected and incubated with malignant (H357) and normal (OKF6) oral keratinocytes to assess extracellular matrix adhesion, epithelial-mesenchymal transition (EMT) and cytokines expression. Incubation of OKF6 with ALC3 and TRI effluent significantly decreased adhesion of the oral keratinocyte to collagen I, whereas incubation of H357 with similar effluent increased adhesion of the oral keratinocyte to laminin I, significantly when compared with incubation with artificial saliva containing serum-free medium (NE; P < 0.05). In OKF6, changes in E-cadherin and vimentin expression were not consistent with EMT although there was evidence of a mesenchymal to epithelial transition in malignant oral keratinocytes incubated with AN and SM effluent. A significant increase of pro-inflammatory cytokines expression, particularly interleukin (IL)-6 and IL-8, was observed when H357 was incubated with all biofilm effluents after 2- and 24-h incubation when compared with NE (P < 0.05). In conclusion, C.albicans, A.naeslundii and S.mutans form polymicrobial biofilms which differentially modulate malignant phenotype of oral keratinocytes.

Dual Transcriptional Profile of Aspergillus flavus during Co-Culture with Listeria monocytogenes and Aflatoxin B1 Production: A Pathogen-Pathogen Interaction

The objective of this study was to investigate the effect of growth temperature and co-culture of Aspergillus flavus with Listeria monocytogenes on the production of Aflatoxin B1 (AFB1) and the transcriptional profile of associated regulatory and biosynthetic genes. The transcription of virulence- and homeostasis-associated genes of L. monocytogenes was also assessed. For this purpose, mono- and co-cultures of L. monocytogenes strain LQC 15257 and A. flavus strain 18.4 were inoculated into Malt Extract broth and allowed to grow for seven days at 25 °C and 30 °C. AFB1 quantification was performed by HPLC analysis and gene expression assessment by RT-qPCR. AFB1 production was lower at 30 °C compared to 25 °C during monoculture and also lower during co-cultures at both temperatures. This was accompanied by downregulation of aflM, aflR, aflP, and aflS during monoculture and aflM and aflS during co-culture at 30 °C. On the other hand, transcription of prfA, plcA, plcB, inlA, inlB, inlJ, murE, accA, acpP, as well as fapR, was not affected. sigB gene was downregulated after co-culture with the fungus at 25 °C and hly was downregulated after monoculture at 30 °C compared to 25 °C. In this work, the molecular interactions between A. flavus and L. monocytogenes were studied for the first time, offering a novel insight into their co-occurrence. Monitoring of their toxigenic and virulence potential at the molecular level revealed a complex dynamic in natural ecosystems.

Multi-omics Analyses Reveal Synergistic Carbohydrate Metabolism in Streptococcus mutans-Candida albicans Mixed-Species Biofilms

Candida albicans, a major opportunistic fungal pathogen, is frequently found together with Streptococcus mutans in dental biofilms associated with severe childhood caries (tooth decay), a prevalent pediatric oral disease. However, the impact of this cross-kingdom relationship on C. albicans remains largely uncharacterized. Here, we employed a novel quantitative proteomics approach in conjunction with transcriptomic profiling to unravel molecular pathways of C. albicans when cocultured with S. mutans in mixed biofilms. RNA sequencing and iTRAQ (isobaric tags for relative and absolute quantitation)-based quantitative proteomics revealed that C. albicans genes and proteins associated with carbohydrate metabolism were significantly enhanced, including sugar transport, aerobic respiration, pyruvate breakdown, and the glyoxylate cycle. Other C. albicans genes and proteins directly and indirectly related to cell morphogenesis and cell wall components such as mannan and glucan were also upregulated, indicating enhanced fungal activity in mixed-species biofilm. Further analyses revealed that S. mutans-derived exoenzyme glucosyltransferase B (GtfB), which binds to the fungal cell surface to promote coadhesion, can break down sucrose into glucose and fructose that can be readily metabolized by C. albicans, enhancing growth and acid production. Altogether, we identified key pathways used by C. albicans in the mixed biofilm, indicating an active fungal role in the sugar metabolism and environmental acidification (key virulence traits associated with caries onset) when interacting with S. mutans, and a new cross-feeding mechanism mediated by GtfB that enhances C. albicans carbohydrate utilization. In addition, we demonstrate that comprehensive transcriptomics and quantitative proteomics can be powerful tools to study microbial contributions which remain underexplored in cross-kingdom biofilms.

Assessing the impact of curcumin on dual-species biofilms formed by Streptococcus mutans and Candida albicans

Streptococcus mutans and Candida albicans are often isolated from plaques associated with early childhood caries. However, there are limited studies examining how these microorganisms interact with one another and how best to manage them. Recent studies have shown that curcumin (CUR), a natural compound, has the potential to independently control both of these microorganisms. The purpose of this study was to investigate how S. mutans and C. albicans respond in mono‐ and dual‐species biofilms challenged with CUR. Quantitative biofilm biomass and viability were first evaluated and supported by live–dead PCR to assess biofilm composition. Confocal laser scanning microscopy (CLSM) was used to evaluate the exopolysaccharide (EPS) content and thickness of the biofilms, and the structure of the biofilms and morphology of the cells were observed by scanning electron microscopy (SEM). Quantitative real‐time PCR (qRT‐PCR) was applied to assess relative gene expression. The 50% minimum biofilm eradication concentration (MBEC₅₀) of CUR against S. mutans and C. albicans was 0.5 mM. The biomass and viability decreased after treatment with CUR both in dual‐species biofilms and in mono‐species biofilm. CUR inhibited S. mutans and C. albicans in both mono‐ and dual‐species biofilms. Streptococcus mutans was more sensitive to CUR in dual‐species biofilm than in mono‐species biofilms, whereas C. albicans was less sensitive in dual‐species biofilms. EPS production was decreased by CUR in both mono‐ and dual‐species biofilms, which coincided with the downregulation of glucosyltransferase and quorum sensing‐related gene expression of S. mutans. In C. albicans, the agglutinin‐like sequence family of C. albicans was also downregulated in dual‐species biofilms. Collectively, these data show the potential benefit of using a natural antimicrobial, CUR, to control caries‐related dual‐species plaque biofilms.

Time-Dependent Changes in Morphostructural Properties and Relative Abundances of Contributors in Pleurotus ostreatus/Pseudomonas alcaliphila Mixed Biofilms

Pleurotus ostreatus dual biofilms with bacteria are known to be involved in rock phosphate solubilization, endophytic colonization, and even in nitrogen fixation. Despite these relevant implications, no information is currently available on the architecture of P. ostreatus-based dual biofilms. In addition to this, there is a limited amount of information regarding the estimation of the temporal changes in the relative abundances of the partners in such binary systems. To address these issues, a dual biofilm model system with this fungus was prepared by using Pseudomonas alcaliphila 34 as the bacterial partner due to its very fast biofilm-forming ability. The application of the bacterial inoculum to already settled fungal biofilm on a polystyrene surface coated with hydroxyapatite was the most efficient approach to the production of the mixed system the ultrastructure of which was investigated by a multi-microscopy approach. Transmission electron microscopy analysis showed that the adhesion of bacterial cells onto the mycelial cell wall appeared to be mediated by the presence of an abundant layer of extracellular matrix (ECM). Scanning electron microscopy analysis showed that ECM filaments of bacterial origin formed initially a reticular structure that assumed a tabular semblance after 72 h, thus overshadowing the underlying mycelial network. Across the thickness of the mixed biofilms, the presence of an extensive network of channels with large aggregates of viable bacteria located on the edges of their lumina was found by confocal laser scanning microscopy; on the outermost biofilm layer, a significant fraction of dead bacterial cells was evident. Albeit with tangible differences, similar results regarding the estimation of the temporal shifts in the relative abundances of the two partners were obtained by two independent methods, the former relying on qPCR targeting of 16S and 18S rRNA genes and the latter on ester-linked fatty acid methyl esters analysis.

Metabolic Signaling and Spatial Interactions in the Oral Polymicrobial Community

Oral supra- and subgingival biofilms are complex communities in which hundreds of bacteria, viruses, and fungi reside and interact. In these social environments, microbes compete and cooperate for resources, such as living space and nutrients. The metabolic activities of bacteria can transform their microenvironment and dynamically influence the fitness and growth of cohabitating organisms. Biofilm communities are temporally and spatially organized largely due to cell-to-cell communication, which promotes synergistic interactions. Metabolic interactions maintain biofilm homeostasis through mutualistic cross-feeding, metabolic syntrophy, and cross-respiration. These interactions include reciprocal metabolite exchanges that promote the growth of physiologically compatible bacteria, processive catabolism of complex substrates, and unidirectional interactions that are globally important for the polymicrobial community. Additionally, oral bacterial interactions can lead to detoxification of oxidative compounds, which will provide protection to the community at large. It has also been established that specific organisms provide terminal electron acceptors to partner species that result in a shift from fermentation to respiration, thus increasing ATP yields and improving fitness. Indeed, many interspecies relationships are multidimensional, and the net outcome can be spatially and temporally dependent. Cross-kingdom interactions also occur as oral yeast are antagonistic to some oral bacteria, while numerous mutualistic interactions contribute to yeast-bacterial colonization, fitness in the oral community, and the pathogenesis of caries. Consideration of this social environment reveals behaviors and phenotypes that are not apparent through the study of microbes in isolation. Here, we provide a comprehensive overview of the metabolic interactions that shape the oral microbial community.

Nanochitosan antimicrobial activity against Streptococcus mutans and Candida albicans dual-species biofilms

OBJECTIVE

Chitosan nanoparticle (nanochitosan) has a broad antimicrobial spectrum against diverse pathogenic microorganisms. However, its effect on dental caries-associated microorganisms, such as Streptococcus mutans and Candida albicans is yet to be explored. These microorganisms are known for causing early childhood caries. Therefore, this study was aimed at investigating nanochitosan inhibition capacity against dual-species biofilms of S. mutans and C. albicans. In this study, nanochitosan antimicrobial activity is reported against mono and dual biofilm species of S. mutans and/or C. albicans at 3 and 18 h incubation time. Nanochitosan inhibition capacity was observed through biofilm mass quantity and cell viability.

RESULTS

The present study successfully synthesized nanochitosan with average diameter of approximately 20-30 nm, and also established dual-species biofilms of S. mutans and C. albicans in vitro. With nanochitosan treatment, the cell viability of both microorganisms significantly decreased with the increasing concentration of nanochitosan. There was no significant decrease in biofilm mass both in the dual and single-species biofilms after 3 h of incubation. However, greater inhibition of biofilm was observed at 18 h incubation.

Interactions between oral commensal Candida and oral bacterial communities in immunocompromised and healthy children

Candida species are usually found as commensal microorganisms in the oral cavity of healthy people. During chemotherapy, cytostatic drugs lead to depletion of the oral flora with the emergence of a dominant bacterial species. The transition from commensal to pathogenic state, further associated with yeast colonization and oral mucositis implies a replacement of the dominant microorganism by Candida albicans. This process goes plausibly through cooperation between C. albicans and bacteria. This study focused on the first step of cooperation between microorganisms isolated from the same oral flora either of leukemic or healthy children. C. albicans isolated from 8/20 children were cultured to display their noninvasive blastosporic yeast form and mixed with their dominant bacteria to study the capacity of planktonic aggregation and the early state of biofilm formation. None of the dominant bacteria opposed the presence of yeast, on the contrary, an interesting cooperation was observed. This behavior is apparently different from that observed when mixing the type strains. In fact, three mutated C. albicans strains display, by their spontaneous ability to form filament, enhanced risks of virulence for leukemic ill carriers. Despite such risks, neither oral nor systemic pathology were observed in ill patients probably because the study was conducted during the first course of chemotherapy and Candida colonization is related to the number of chemotherapeutic cycles. The presence of C. albicans during the initial cycle represents, by its ability to interact with oral bacteria, an actual threat for further cures.

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.

Cross-Domain and Viral Interactions in the Microbiome

The importance of the microbiome to human health is increasingly recognized and has become a major focus of recent research. However, much of the work has focused on a few aspects, particularly the bacterial component of the microbiome, most frequently in the gastrointestinal tract. Yet humans and other animals can be colonized by a wide array of organisms spanning all domains of life, including bacteria and archaea, unicellular eukaryotes such as fungi, multicellular eukaryotes such as helminths, and viruses. As they share the same host niches, they can compete with, synergize with, and antagonize each other, with potential impacts on their host. Here, we discuss these major groups making up the human microbiome, with a focus on how they interact with each other and their multicellular host.

The bare necessities: Uncovering essential and condition-critical genes with transposon sequencing

Querying gene function in bacteria has been greatly accelerated by the advent of transposon sequencing (Tn-seq) technologies (related Tn-seq strategies are known as TraDIS, INSeq, RB-TnSeq, and HITS). Pooled populations of transposon mutants are cultured in an environment and next-generation sequencing tools are used to determine areas of the genome that are important for bacterial fitness. In this review we provide an overview of Tn-seq methodologies and discuss how Tn-seq has been applied, or could be applied, to the study of oral microbiology. These applications include studying the essential genome as a means to rationally design therapeutic agents. Tn-seq has also contributed to our understanding of well-studied biological processes in oral bacteria. Other important applications include in vivo pathogenesis studies and use of Tn-seq to probe the molecular basis of microbial interactions. We also highlight recent advancements in techniques that act in synergy with Tn-seq such as clustered regularly interspaced short palindromic repeats (CRISPR) interference and microfluidic chip platforms.