Interaction of Candida albicans cell wall Als3 protein with Streptococcus gordonii SspB adhesin promotes development of mixed-species communities

Modulation of Candida albicans virulence by bacterial biofilms on titanium surfaces

Whilst Candida albicans occurs in peri-implant biofilms, its role in peri-implantitis remains unclear. This study therefore examined the virulence of C. albicans in mixed-species biofilms on titanium surfaces. Biofilms of C. albicans (Ca), C. albicans with streptococci (Streptococcus sanguinis, S. mutans) (Ca-Ss-Sm) and those incorporating Porphyromonas gingivalis (Ca-Pg and Ca-Ss-Sm-Pg) were developed. Expression of C. albicans genes associated with adhesion (ALS1, ALS3, HWP1) and hydrolytic enzymes (SAP2, SAP4, SAP6, PLD1) was measured and hyphal production by C. albicans quantified. Compared with Ca biofilms, significant (p<0.05) up-regulation of ALS3, HWP1, SAP2 and SAP6, and hyphal production occurred in biofilms containing streptococci (Ca-Ss-Sm). In Ca-Pg biofilms, down-regulation of HWP1 and SAP4 expression, with reduced hyphal production occurred. Ca-Ss-Sm-Pg biofilms had increased hyphal proportions and up-regulation of ALS3, SAP2 and SAP6. In conclusion, C. albicans expressed virulence factors in biofilms that could contribute to peri-implantitis, but this was dependent on associated bacterial species.

Experimental Models of C. albicans-Streptococcal Co-infection

Interactions of C. albicans with co-colonizing bacteria at mucosal sites can be synergistic or antagonistic in disease development, depending on the bacterial species and mucosal site. Mitis group streptococci and C. albicans colonize the oral mucosa of the majority of healthy individuals. These streptococci have been termed "accessory pathogens," defined by their ability to initiate multispecies biofilm assembly and promote the virulence of the mixed bacterial biofilm community in which they participate. To demonstrate whether interactions with Mitis group streptococci limit or promote the potential of C. albicans to become an opportunistic pathogen, in vitro and in vivo co-infection models are needed. Here, we describe two C. albicans-streptococcal co-infection models: an organotypic oral mucosal tissue model that incorporates salivary flow and a mouse model of oral co-infection that requires reduced levels of immunosuppression compared to single fungal infection.

Biofilm formation and Candida albicans morphology on the surface of denture base materials

Fungal biofilms may contribute to the occurrence of denture stomatitis. The objective of the study was to investigate the biofilm formation and morphology of Candida albicans in biofilms on the surface of denture base materials. Specimens were prepared from different denture base materials. After determination of surface properties and salivary pellicle formation, mono- and multispecies biofilm formation including Candida albicans ATCC 10231 was initiated. Relative amounts of adherent cells were determined after 20, 44, 68 and 188 h; C. albicans morphology was analysed employing selective fluorescence microscopic analysis. Significant differences were identified in the relative amount of cells adherent to the denture base materials. Highest blastospore/hyphae index suggesting an increased percentage of hyphae was observed in mono- and multispecies biofilms on the soft denture liner, which did not necessarily respond to the highest relative amount of adherent cells. For both biofilm models, lowest relative amount of adherent cells was identified on the methacrylate-based denture base material, which did not necessarily relate to a significantly lower blastospore/hyphae index. The results indicate that there are significant differences in both biofilm formation as well as the morphology of C. albicans cells in biofilms on the surface of different denture base materials.

Adaptations of the Secretome of Candida albicans in Response to Host-Related Environmental Conditions

The wall proteome and the secretome of the fungal pathogen Candida albicans help it to thrive in multiple niches of the human body. Mass spectrometry has allowed researchers to study the dynamics of both subproteomes. Here, we discuss some major responses of the secretome to host-related environmental conditions. Three β-1,3-glucan-modifying enzymes, Mp65, Sun41, and Tos1, are consistently found in large amounts in culture supernatants, suggesting that they are needed for construction and expansion of the cell wall β-1,3-glucan layer and thus correlate with growth and might serve as diagnostic biomarkers. The genes ENG1, CHT3, and SCW11, which encode an endoglucanase, the major chitinase, and a β-1,3-glucan-modifying enzyme, respectively, are periodically expressed and peak in M/G₁. The corresponding protein abundances in the medium correlate with the degree of cell separation during single-yeast-cell, pseudohyphal, and hyphal growth. We also discuss the observation that cells treated with fluconazole, or other agents causing cell surface stress, form pseudohyphal aggregates. Fluconazole-treated cells secrete abundant amounts of the transglucosylase Phr1, which is involved in the accumulation of β-1,3-glucan in biofilms, raising the question whether this is a general response to cell surface stress. Other abundant secretome proteins also contribute to biofilm formation, emphasizing the important role of secretome proteins in this mode of growth. Finally, we discuss the relevance of these observations to therapeutic intervention. Together, these data illustrate that C. albicans actively adapts its secretome to environmental conditions, thus promoting its survival in widely divergent niches of the human body.

The Candida albicans agglutinin-like sequence family of adhesins: functional insights gained from structural analysis

Candida albicans colonizes many host sites suggesting its interaction with diverse ligands. Candida albicans adhesion is mediated by a number of proteins including those in the Als (agglutinin-like sequence) family, which have been studied intensively. The recent solution of the Als binding domain structure ended years of speculation regarding the molecular mechanism for Als adhesive function. Als adhesins bind flexible C termini from a broad collection of proteins, providing the basis for adhesion to various cell types and perhaps for C. albicans broad tissue tropism. Understanding adhesive functions at the molecular level will reveal the sequence of events in C. albicans pathogenesis, from host recognition to complex interactions such as development of polymicrobial biofilms or disseminated disease.

Transcriptome analysis of Streptococcus gordonii Challis DL1 indicates a role for the biofilm-associated fruRBA operon in response to Candida albicans

Multiple levels of interkingdom signaling have been implicated in maintaining the ecological balance between Candida albicans and commensal streptococci to assure a state of oral health. To better understand the molecular mechanisms involved in the initial streptococcal response to the presence of C. albicans that can initiate oral surface colonization and biofilm formation, hypha-forming cells were incubated with Streptococcus gordonii cells for 30 min to assess the streptococcal transcriptome response. A genome-wide microarray analysis and quantitative polymerase chain reaction validation of S. gordonii transcripts identified a number of genes, the majority of which were involved in metabolic functions that were differentially expressed in the presence of hyphae. The fruR, fruB, and fruA genes encoding the transcriptional regulator, fructose-1-phosphate kinase, and fructose-specific permease, respectively, of the phosphoenolpyruvate-dependent fructose phosphotransferase system, were consistently upregulated. An S. gordonii mutant in which these genes were deleted by allelic replacement formed an architecturally distinct, less robust biofilm with C. albicans than did parental strain cells. Complementing the mutant with plasmid borne fruR, fruB, and fruA genes caused phenotype reversion, indicating that the genes in this operon played a role in dual-species biofilm formation. This genome-wide analysis of the S. gordonii transcriptional response to C. albicans has identified several genes that have potential roles in interkingdom signaling and responses.

Fungal-bacterial interactions and their relevance in health

Cross-kingdom interactions between bacteria and fungi are a common occurrence in the environment. Recent studies have identified various types of interactions that either can take the form of a synergistic relationship or can result in an antagonistic interplay with the subsequent destruction or inhibition of growth of bacteria, fungi or both. This cross-kingdom communication is of particular significance in human health and disease, as bacteria and fungi commonly colonize various human surfaces and their interactions can at times alter the outcome of invasive infections. Moreover, mixed infections from both bacteria and fungi are relatively common among critically ill patients and individuals with weak immune responses. The purpose of this review is to summarize our knowledge on the type of interactions between bacteria and fungi and their relevance in human infections.

Analysis of the influence of parenteral cancer chemotherapy on the health condition of oral mucosa

AIM OF THE STUDY

The present study was aimed at estimating the prevalence of oral complications in cancer patients receiving chemotherapy.

MATERIAL AND METHODS

The study was conducted on a group of 58 patients treated with chemotherapy (study group). The control group consisted of 30 healthy patients. Dental status and oral mucosa were examined using the criteria of the National Cancer Institute Toxicity Criteria Scale. The levels of stimulated and unstimulated saliva flow were analysed.

RESULTS

In the group of patients treated with chemotherapy, 59% of patients had inflammatory changes of the soft tissues of the mouth, such as erythema, erosions, or ulcers, which were discovered during dental examination. Such changes occurred in only 10% of patients in the control group. Six of the patients treated with chemotherapy reported pain with intensity was so severe that it caused swallowing difficulties. Patients in the study group frequently complained about the presence of dry mouth, taste disturbances, nausea, and vomiting. These symptoms occurred in 70% of patients undergoing oncological treatment. In both stimulated and unstimulated saliva secretion, the rates were significantly lower in patients from the research group, when compared to the control group.

Cellular Components Mediating Coadherence of Candida albicans and Fusobacterium nucleatum

Candida albicans is an opportunistic fungal pathogen found as part of the normal oral flora. It can be coisolated with Fusobacterium nucleatum, an opportunistic bacterial pathogen, from oral disease sites, such as those involved in refractory periodontitis and pulp necrosis. The physical coadherence between these 2 clinically important microbes has been well documented and suggested to play a role in facilitating their oral colonization and colocalization and contributing to polymicrobial pathogenesis. Previous studies indicated that the physical interaction between C. albicans and F. nucleatum was mediated by the carbohydrate components on the surface of C. albicans and the protein components on the Fusobaterium cell surface. However, the identities of the components involved still remain elusive. This study was aimed at identifying the genetic determinants involved in coaggregation between the 2 species. By screening a C. albicans SN152 mutant library and a panel of F. nucleatum 23726 outer membrane protein mutants, we identified FLO9, which encodes a putative adhesin-like cell wall mannoprotein of C. albicans and radD, an arginine-inhibitable adhesin-encoding gene in F. nucleatum that is involved in interspecies coadherence. Consistent with these findings, we demonstrated that the strong coaggregation between wild-type F. nucleatum 23726 and C. albicans SN152 in an in vitro assay could be greatly inhibited by arginine and mannose. Our study also suggested a complex multifaceted mechanism underlying physical interaction between C. albicans and F. nucleatum and for the first time revealed the identity of major genetic components involved in mediating the coaggregation. These observations provide useful knowledge for developing new targeted treatments for disrupting interactions between these 2 clinically relevant pathogens.

Innocent until proven guilty: mechanisms and roles of Streptococcus-Candida interactions in oral health and disease

Candida albicans and streptococci of the mitis group colonize the oral cavities of the majority of healthy humans. While C. albicans is considered an opportunistic pathogen, streptococci of this group are broadly considered avirulent or even beneficial organisms. However, recent evidence suggests that multi-species biofilms with these organisms may play detrimental roles in host homeostasis and may promote infection. In this review we summarize the literature on molecular interactions between members of this streptococcal group and C. albicans, with emphasis on their potential role in the pathogenesis of opportunistic oral mucosal infections.

Shaping the oral mycobiota: interactions of opportunistic fungi with oral bacteria and the host

The oral mycobiota is an important component of the oral microbiota that has only recently received increased attention. The diversity and complexity of the oral mycobiota in healthy humans is greater than any other body site. Dysbiotic imbalance of indigenous fungal communities in immunosuppressed hosts has been proposed to lead to oropharyngeal fungal infections. As in other body sites, to survive and thrive in the oral cavity fungi have to maintain mutually beneficial relationships with the resident bacterial microbiota and the host. Here we review our current understanding of the composition of the oral mycobiota and how it may be influenced by oral commensal bacteria and the host environment.

Dressed to impress: impact of environmental adaptation on the Candida albicans cell wall

Candida albicans is an opportunistic fungal pathogen of humans causing superficial mucosal infections and life‐threatening systemic disease. The fungal cell wall is the first point of contact between the invading pathogen and the host innate immune system. As a result, the polysaccharides that comprise the cell wall act as pathogen associated molecular patterns, which govern the host–pathogen interaction. The cell wall is dynamic and responsive to changes in the external environment. Therefore, the host environment plays a critical role in regulating the host–pathogen interaction through modulation of the fungal cell wall. This review focuses on how environmental adaptation modulates the cell wall structure and composition, and the subsequent impact this has on the innate immune recognition of C. albicans.

Functional Advantages of Porphyromonas gingivalis Vesicles

Porphyromonas gingivalis is a keystone pathogen of periodontitis. Outer membrane vesicles (OMVs) have been considered as both offense and defense components of this bacterium. Previous studies indicated that like their originating cells, P. gingivalis vesicles, are able to invade oral epithelial cells and gingival fibroblasts, in order to promote aggregation of some specific oral bacteria and to induce host immune responses. In the present study, we investigated the invasive efficiency of P. gingivalis OMVs and compared results with that of the originating cells. Results revealed that 70-90% of human primary oral epithelial cells, gingival fibroblasts, and human umbilical vein endothelial cells carried vesicles from P. gingivalis 33277 after being exposed to the vesicles for 1 h, while 20-50% of the host cells had internalized P. gingivalis cells. We also detected vesicle-associated DNA and RNA and a vesicle-mediated horizontal gene transfer in P. gingivalis strains, which represents a novel mechanism for gene transfer between P. gingivalis strains. Moreover, purified vesicles of P. gingivalis appear to have a negative impact on biofilm formation and the maintenance of Streptococcus gordonii. Our results suggest that vesicles are likely the best offence weapon of P. gingivalis for bacterial survival in the oral cavity and for induction of periodontitis.

Candida-streptococcal mucosal biofilms display distinct structural and virulence characteristics depending on growth conditions and hyphal morphotypes

Candida albicans and streptococci of the mitis group form communities in multiple oral sites, where moisture and nutrient availability can change spatially or temporally. This study evaluated structural and virulence characteristics of Candida-streptococcal biofilms formed on moist or semidry mucosal surfaces, and tested the effects of nutrient availability and hyphal morphotype on dual-species biofilms. Three-dimensional models of the oral mucosa formed by immortalized keratinocytes on a fibroblast-embedded collagenous matrix were used. Infections were carried out using Streptococcus oralis strain 34, in combination with a C. albicans wild-type strain, or pseudohyphal-forming mutant strains. Increased moisture promoted a homogeneous surface biofilm by C. albicans. Dual biofilms had a stratified structure, with streptococci growing in close contact with the mucosa and fungi growing on the bacterial surface. Under semidry conditions, Candida formed localized foci of dense growth, which promoted focal growth of streptococci in mixed biofilms. Candida biofilm biovolume was greater under moist conditions, albeit with minimal tissue invasion, compared with semidry conditions. Supplementing the infection medium with nutrients under semidry conditions intensified growth, biofilm biovolume and tissue invasion/damage, without changing biofilm structure. Under these conditions, the pseudohyphal mutants and S. oralis formed defective superficial biofilms, with most bacteria in contact with the epithelial surface, below a pseudohyphal mass, resembling biofilms growing in a moist environment. The presence of S. oralis promoted fungal invasion and tissue damage under all conditions. We conclude that moisture, nutrient availability, hyphal morphotype and the presence of commensal bacteria influence the architecture and virulence characteristics of mucosal fungal biofilms.

Interkingdom networking within the oral microbiome

Different sites within the oropharynx harbour unique microbial communities. Co-evolution of microbes and host has resulted in complex interkingdom circuitries. Metabolic signalling is crucial to these processes, and novel microbial communication factors are progressively being discovered. Resolving interkingdom networks will lead to better understanding of oral health or disease aetiology.

Candida survival strategies

Only few Candida species, e.g., Candida albicans, Candida glabrata, Candida dubliniensis, and Candida parapsilosis, are successful colonizers of a human host. Under certain circumstances these species can cause infections ranging from superficial to life-threatening disseminated candidiasis. The success of C. albicans, the most prevalent and best studied Candida species, as both commensal and human pathogen depends on its genetic, biochemical, and morphological flexibility which facilitates adaptation to a wide range of host niches. In addition, formation of biofilms provides additional protection from adverse environmental conditions. Furthermore, in many host niches Candida cells coexist with members of the human microbiome. The resulting fungal-bacterial interactions have a major influence on the success of C. albicans as commensal and also influence disease development and outcome. In this chapter, we review the current knowledge of important survival strategies of Candida spp., focusing on fundamental fitness and virulence traits of C. albicans.

Streptococcus gordonii comCDE (competence) operon modulates biofilm formation with Candida albicans

Candida albicans is a pleiomorphic fungus that forms mixed species biofilms with Streptococcus gordonii, an early colonizer of oral cavity surfaces. Activation of quorum sensing (QS; intercellular signalling) promotes monospecies biofilm development by these micro-organisms, but the role of QS in mixed species communities is not understood. The comCDE genes in S. gordonii encode a sensor-regulator system (ComDE), which is activated by the comC gene product (CSP, competence stimulating peptide) and modulates expression of QS-regulated genes. Dual species biofilms of S. gordonii ΔcomCDE or ΔcomC mutants with C. albicans showed increased biomass compared to biofilms of S. gordonii DL1 wild-type with C. albicans. The ΔcomCDE mutant dual species biofilms in particular contained more extracellular DNA (eDNA), and could be dispersed with DNase I or protease treatment. Exogenous CSP complemented the S. gordonii ΔcomC transformation deficiency, as well as the ΔcomC-C. albicans biofilm phenotype. Purified CSP did not affect C. albicans hyphal filament formation but inhibited monospecies biofilm formation by C. albicans. The results suggest that the S. gordonii comCDE QS-system modulates the production of eDNA and the incorporation of C. albicans into dual species biofilms.

Effects of Nicotine on Streptococcus gordonii Growth, Biofilm Formation, and Cell Aggregation

Streptococcus gordonii is a commensal species of human oral flora. It initiates dental biofilm formation and provides binding sites for later colonizers to attach to and generate mature biofilm. Smoking is the second highest risk factor for periodontal disease, and cigarette smoke extract has been reported to facilitate Porphyromonas gingivalis-S. gordonii dual-species biofilm formation. Our hypothesis is that nicotine, one of the most important and active components of tobacco, stimulates S. gordonii multiplication and aggregation. In the present study, S. gordonii planktonic cell growth (kinetic absorbance and CFU), biofilm formation (crystal violet stain and confocal laser scanning microscopy [CLSM]), aggregation with/without sucrose, and 11 genes that encode binding proteins or regulators of gene expression were investigated. Results demonstrated planktonic cell growth was stimulated by 1 to 4 mg/ml nicotine treatment. Biofilm formation was increased at 0.5 to 4 mg/ml nicotine. CLSM indicated bacterial cell mass was increased by 2 and 4 mg/ml nicotine, but biofilm extracellular polysaccharide was not significantly affected by nicotine. Cell aggregation was upregulated by 4, 8, and 16 mg/ml nicotine with sucrose and by 16 mg/ml nicotine without sucrose. Quantitative reverse transcriptase PCR indicated S. gordonii abpA, scaA, ccpA, and srtA were upregulated in planktonic cells by 2 mg/ml nicotine. In conclusion, nicotine stimulates S. gordonii planktonic cell growth, biofilm formation, aggregation, and gene expression of binding proteins. Those effects may promote later pathogen attachment to tooth surfaces, the accumulation of tooth calculus, and the development of periodontal disease in cigarette smokers.

A proposed mechanism for the interaction between the Candida albicans Als3 adhesin and streptococcal cell wall proteins

C. albicans binds various bacteria, including the oral commensal Streptococcus gordonii. Published reports documented the role of C. albicans Als3 and S. gordonii SspB in this interaction, and the importance of the Als N-terminal domain (NT-Als) in C. albicans adhesion. Here, we demonstrate that Als1 also binds S. gordonii. We also describe use of the NT-Als crystal structure to design mutations that precisely disrupt peptide-binding cavity (PBC) or amyloid-forming region (AFR) function in Als3. C. albicans displaying Als3 PBC mutant proteins showed significantly reduced binding to S. gordonii; mutation of the AFR did not affect the interaction. These observations present an enigma: the Als PBC binds free C termini of ligands, but the SspB C terminus is covalently linked to peptidoglycan and thus unavailable as a ligand. These observations and the predicted SspB elongated structure suggest that partial proteolysis of streptococcal cell wall proteins is necessary for recognition by Als adhesins.

Physiological adaptations of key oral bacteria

Oral colonising bacteria are highly adapted to the various environmental niches harboured within the mouth, whether that means while contributing to one of the major oral diseases of caries, pulp infections, or gingival/periodontal disease or as part of a commensal lifestyle. Key to these infections is the ability to adhere to surfaces via a range of specialised adhesins targeted at both salivary and epithelial proteins, their glycans and to form biofilm. They must also resist the various physical stressors they are subjected to, including pH and oxidative stress. Possibly most strikingly, they have developed the ability to harvest both nutrient sources provided by the diet and those derived from the host, such as protein and surface glycans. We have attempted to review recent developments that have revealed much about the molecular mechanisms at work in shaping the physiology of oral bacteria and how we might use this information to design and implement new treatment strategies.

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

Polymicrobial biofilms are of large medical importance, but relatively little is known about the role of interspecies interactions for their physiology and virulence. Here, we studied two human pathogens co-occuring in the oral cavity, the opportunistic fungus Candida albicans and the caries-promoting bacterium Streptococcus mutans. Dual-species biofilms reached higher biomass and cell numbers than mono-species biofilms, and the production of extracellular polymeric substances (EPSs) by S. mutans was strongly suppressed, which was confirmed by scanning electron microscopy, gas chromatography-mass spectrometry and transcriptome analysis. To detect interkingdom communication, C. albicans was co-cultivated with a strain of S. mutans carrying a transcriptional fusion between a green fluorescent protein-encoding gene and the promoter for sigX, the alternative sigma factor of S. mutans, which is induced by quorum sensing signals. Strong induction of sigX was observed in dual-species biofilms, but not in single-species biofilms. Conditioned media from mixed biofilms but not from C. albicans or S. mutans cultivated alone activated sigX in the reporter strain. Deletion of comS encoding the synthesis of the sigX-inducing peptide precursor abolished this activity, whereas deletion of comC encoding the competence-stimulating peptide precursor had no effect. Transcriptome analysis of S. mutans confirmed induction of comS, sigX, bacteriocins and the downstream late competence genes, including fratricins, in dual-species biofilms. We show here for the first time the stimulation of the complete quorum sensing system of S. mutans by a species from another kingdom, namely the fungus C. albicans, resulting in fundamentally changed virulence properties of the caries pathogen.

Systemic Staphylococcus aureus infection mediated by Candida albicans hyphal invasion of mucosal tissue

Candida albicans and Staphylococcus aureus are often co-isolated in cases of biofilm-associated infections. C. albicans can cause systemic disease through morphological switch from the rounded yeast to the invasive hyphal form. Alternatively, systemic S. aureus infections arise from seeding through breaks in host epithelial layers although many patients have no documented portal of entry. We describe a novel strategy by which S. aureus is able to invade host tissue and disseminate via adherence to the invasive hyphal elements of Candida albicans. In vitro and ex vivo findings demonstrate a specific binding of the staphylococci to the candida hyphal elements. The C. albicans cell wall adhesin Als3p binds to multiple staphylococcal adhesins. Furthermore, Als3p is required for C. albicans to transport S. aureus into the tissue and cause a disseminated infection in an oral co-colonization model. These findings suggest that C. albicans can facilitate the invasion of S. aureus across mucosal barriers, leading to systemic infection in co-colonized patients.

Anaerobic bacteria grow within Candida albicans biofilms and induce biofilm formation in suspension cultures

The human microbiome contains diverse microorganisms, which share and compete for the same environmental niches. A major microbial growth form in the human body is the biofilm state, where tightly packed bacterial, archaeal, and fungal cells must cooperate and/or compete for resources in order to survive. We examined mixed biofilms composed of the major fungal species of the gut microbiome, Candida albicans, and each of five prevalent bacterial gastrointestinal inhabitants: Bacteroides fragilis, Clostridium perfringens, Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecalis. We observed that biofilms formed by C. albicans provide a hypoxic microenvironment that supports the growth of two anaerobic bacteria, even when cultured in ambient oxic conditions that are normally toxic to the bacteria. We also found that coculture with bacteria in biofilms induces massive gene expression changes in C. albicans, including upregulation of WOR1, which encodes a transcription regulator that controls a phenotypic switch in C. albicans, from the "white" cell type to the "opaque" cell type. Finally, we observed that in suspension cultures, C. perfringens induces aggregation of C. albicans into "mini-biofilms," which allow C. perfringens cells to survive in a normally toxic environment. This work indicates that bacteria and C. albicans interactions modulate the local chemistry of their environment in multiple ways to create niches favorable to their growth and survival.

Functional regions of Candida albicans hyphal cell wall protein Als3 that determine interaction with the oral bacterium Streptococcus gordonii

The opportunistic pathogen Candida albicans colonizes the oral cavity and gastrointestinal tract. Adherence to host cells, extracellular matrix and salivary glycoproteins that coat oral surfaces, including prostheses, is an important prerequisite for colonization. In addition, interactions of C. albicans with commensal oral streptococci are suggested to promote retention and persistence of fungal cells in mixed-species communities. The hyphal filament specific cell wall protein Als3, a member of the Als protein family, is a major determinant in C. albicans adherence. Here, we utilized site-specific in-frame deletions within Als3 expressed on the surface of heterologous Saccharomyces cerevisiae to determine regions involved in interactions of Als3 with Streptococcus gordonii. N-terminal region amino acid residue deletions Δ166-225, Δ218-285, Δ270-305 and Δ277-286 were each effective in inhibiting binding of Strep. gordonii to Als3. In addition, these deletions differentially affected biofilm formation, hydrophobicity, and adherence to silicone and human tissue proteins. Deletion of the central repeat domain (Δ434-830) did not significantly affect interaction of Als3 with Strep. gordonii SspB protein, but affected other adherence properties and biofilm formation. Deletion of the amyloid-forming region (Δ325-331) did not affect interaction of Als3 with Strep. gordonii SspB adhesin, suggesting this interaction was amyloid-independent. These findings highlighted the essential function of the N-terminal domain of Als3 in mediating the interaction of C. albicans with S. gordonii, and suggested that amyloid formation is not essential for the inter-kingdom interaction.

Fungal-bacterial interactions and their relevance to oral health: linking the clinic and the bench

High throughput sequencing has accelerated knowledge on the oral microbiome. While the bacterial component of oral communities has been extensively characterized, the role of the fungal microbiota in the oral cavity is largely unknown. Interactions among fungi and bacteria are likely to influence oral health as exemplified by the synergistic relationship between Candida albicans and oral streptococci. In this perspective, we discuss the current state of the field of fungal-bacterial interactions in the context of the oral cavity. We highlight the need to conduct longitudinal clinical studies to simultaneously characterize the bacterial and fungal components of the human oral microbiome in health and during disease progression. Such studies need to be coupled with investigations using disease-relevant models to mechanistically test the associations observed in humans and eventually identify fungal-bacterial interactions that could serve as preventive or therapeutic targets for oral diseases.

The peptide-binding cavity is essential for Als3-mediated adhesion of Candida albicans to human cells

The adhesive phenotype of Candida albicans contributes to its ability to colonize the host and cause disease. Als proteins are one of the most widely studied C. albicans virulence attributes; deletion of ALS3 produces the greatest reduction in adhesive function. Although adhesive activity is thought to reside within the N-terminal domain of Als proteins (NT-Als), the molecular mechanism of adhesion remains unclear. We designed mutations in NT-Als3 that test the contribution of the peptide-binding cavity (PBC) to C. albicans adhesion and assessed the adhesive properties of other NT-Als3 features in the absence of a functional PBC. Structural analysis of purified loss-of-PBC-function mutant proteins showed that the mutations did not alter the overall structure or surface properties of NT-Als3. The mutations were incorporated into full-length ALS3 and integrated into the ALS3 locus of a deletion mutant, under control of the native ALS3 promoter. The PBC mutant phenotype was evaluated in assays using monolayers of human pharyngeal epithelial and umbilical vein endothelial cells, and freshly collected human buccal epithelial cells in suspension. Loss of PBC function resulted in an adhesion phenotype that was indistinguishable from the Δals3/Δals3 strain. The adhesive contribution of the Als3 amyloid-forming-region (AFR) was also tested using these methods. C. albicans strains producing cell surface Als3 in which the amyloidogenic potential was destroyed showed little contribution of the AFR to adhesion, instead suggesting an aggregative function for the AFR. Collectively, these results demonstrate the essential and principal role of the PBC in Als3 adhesion.

O-mannosylation in Candida albicans enables development of interkingdom biofilm communities

Candida albicans is a fungus that colonizes oral cavity surfaces, the gut, and the genital tract. Streptococcus gordonii is a ubiquitous oral bacterium that has been shown to form biofilm communities with C. albicans. Formation of dual-species S. gordonii-C. albicans biofilm communities involves interaction of the S. gordonii SspB protein with the Als3 protein on the hyphal filament surface of C. albicans. Mannoproteins comprise a major component of the C. albicans cell wall, and in this study we sought to determine if mannosylation in cell wall biogenesis of C. albicans was necessary for hyphal adhesin functions associated with interkingdom biofilm development. A C. albicans mnt1Δ mnt2Δ mutant, with deleted α-1,2-mannosyltransferase genes and thus defective in O-mannosylation, was abrogated in biofilm formation under various growth conditions and produced hyphal filaments that were not recognized by S. gordonii. Cell wall proteomes of hypha-forming mnt1Δ mnt2Δ mutant cells showed growth medium-dependent alterations, compared to findings for the wild type, in a range of protein components, including Als1, Als3, Rbt1, Scw1, and Sap9. Hyphal filaments formed by mnt1Δ mnt2Δ mutant cells, unlike wild-type hyphae, did not interact with C. albicans Als3 or Hwp1 partner cell wall proteins or with S. gordonii SspB partner adhesin, suggesting defective functionality of adhesins on the mnt1Δ mnt2Δ mutant. These observations imply that early stage O-mannosylation is critical for activation of hyphal adhesin functions required for biofilm formation, recognition by bacteria such as S. gordonii, and microbial community development. IMPORTANCE In the human mouth, microorganisms form communities known as biofilms that adhere to the surfaces present. Candida albicans is a fungus that is often found within these biofilms. We have focused on the mechanisms by which C. albicans becomes incorporated into communities containing bacteria, such as Streptococcus. We find that impairment of early stage addition of mannose sugars to C. albicans hyphal filament proteins deleteriously affects their subsequent performance in mediating formation of polymicrobial biofilms. Our analyses provide new understanding of the way that microbial communities develop, and of potential means to control C. albicans infections.

Review article: fungal microbiota and digestive diseases

BACKGROUND

The role of the fungal microbiota in digestive diseases is poorly defined, but is becoming better understood due to advances in metagenomics.

AIM

To review the gastrointestinal fungal microbiota and its relationship with digestive diseases.

METHODS

Search of the literature using PubMed and MEDLINE databases. Subject headings including 'fungal-bacterial interactions', 'mycotoxins', 'immunity to fungi', 'fungal infection', 'fungal microbiota', 'mycobiome' and 'digestive diseases' were used.

RESULTS

The fungal microbiota is an integral part of the gastrointestinal microecosystem with up to 10(6) microorganisms per gram of faeces. Next-generation sequencing of the fungal 18S rRNA gene has allowed better characterisation of the gastrointestinal mycobiome. Numerous interactions between fungi and bacteria and the complex immune response to gastrointestinal commensal or pathogenic fungi all impact on the pathophysiology of inflammatory bowel disease and other gastrointestinal inflammatory entities such as peptic ulcers. Mycotoxins generated as fungal metabolites contribute to disturbances of gastrointestinal barrier and immune functions and are associated with chronic intestinal inflammatory conditions as well as hepatocellular and oesophagogastric cancer. Systemic and gastrointestinal disease can also lead to secondary fungal infections. Fungal genomic databases and methodologies need to be further developed and will allow a much better understanding of the diversity and function of the mycobiome in gastrointestinal inflammation, tumourigenesis, liver cirrhosis and transplantation, and its alteration as a consequence of antibiotic therapy and chemotherapy.

CONCLUSIONS

The fungal microbiota and its metabolites impact gastrointestinal function and contribute to the pathogenesis of digestive diseases. Further metagenomic analyses of the gastrointestinal mycobiome in health and disease is needed.

Sexual biofilm formation in Candida tropicalis opaque cells

Candida albicans and Candida tropicalis are opportunistic fungal pathogens that can transition between white and opaque phenotypic states. White and opaque cells differ both morphologically and in their responses to environmental signals. In C. albicans, opaque cells respond to sexual pheromones by undergoing conjugation, while white cells are induced by pheromones to form sexual biofilms. Here, we show that sexual biofilm formation also occurs in C. tropicalis but, unlike C. albicans, biofilms are formed exclusively by opaque cells. C. tropicalis biofilm formation was dependent on the pheromone receptors Ste2 and Ste3, confirming the role of pheromone signalling in sexual biofilm development. Structural analysis of C. tropicalis sexual biofilms revealed stratified communities consisting of a basal layer of yeast cells and an upper layer of filamentous cells, together with an extracellular matrix. Transcriptional profiling showed that genes involved in pheromone signalling and conjugation were upregulated in sexual biofilms. Furthermore, FGR23, which encodes an agglutinin-like protein, was found to enhance both mating and sexual biofilm formation. Together, these studies reveal that C. tropicalis opaque cells form sexual biofilms with a complex architecture, and suggest a conserved role for sexual agglutinins in mediating mating, cell cohesion and biofilm formation.

Candida and Other Fungal Species

In the last half-decade or so, interest in the bacterial part of the human microbiome and its role in maintaining health have received considerable attention. Since 2009, over 300 publications have appeared describing the oral bacterial microbiome. Strikingly, fungi in the oral cavity have been studied exclusively in relation to pathologies. However, little to nothing is known about a role of fungi in establishing and maintaining a healthy oral ecology. In a healthy ecology, balance is maintained by the combined positive and negative influences between and among its members. Interactions between fungi and bacteria occur primarily at a physical and chemical level. Physical interactions are represented by (co-)adhesion and repulsion (exclusion), while chemical interactions include metabolic dependencies, quorum-sensing, and the production of antimicrobial agents. Information obtained from oral model systems and also from studies on the role of fungi in gastro-intestinal ecology indicates that fungi influence bacterial behavior through these different interactions. This review describes our current knowledge of the interactions between fungi and bacteria and aims to illustrate that further research is required to establish the role of fungi in maintaining a healthy oral cavity.

Microbial cell surface proteins and secreted metabolites involved in multispecies biofilms

A considerable number of infectious diseases involve multiple microbial species coexisting and interacting in a host. Only recently however the impact of these polymicrobial diseases has been appreciated and investigated. Often, the causative microbial species are embedded in an extracellular matrix forming biofilms, a form of existence that offers protection against chemotherapeutic agents and host immune defenses. Therefore, recent efforts have focused on developing novel therapeutic strategies targeting biofilm-associated polymicrobial infections, a task that has proved to be challenging. One promising approach to inhibit the development of such complex infections is to impede the interactions between the microbial species via inhibition of adhesion. To that end, studies have focused on identifying specific cell wall adhesins and receptors involved in the interactions between the various bacterial species and the most pathogenic human fungal species Candida albicans. This review highlights the important findings from these studies and describes the available tools and techniques that have provided insights into the role of secreted molecules orchestrating microbial interactions in biofilms. Specifically, we focus on the interactions that take place in oral biofilms and the implications of these interactions on oral health and therapeutic strategies.

Peptide detection of fungal functional amyloids in infected tissue

Many fungal cell adhesion proteins form functional amyloid patches on the surface of adhering cells. The Candida albicansAgglutinin-like sequence (Als) adhesins are exemplars for this phenomenon, and have amyloid forming sequences that are conserved between family members. The Als5p amyloid sequence mediates amyloid fibril formation and is critical for cell adhesion and biofilm formation, and is also present in the related adhesins Als1p and Als3p. We have developed a fluorescent peptide probe containing the conserved Als amyloid-forming sequence. This peptide bound specifically to yeast expressing Als5p, but not to cells lacking the adhesin. The probe bound to both yeast and hyphal forms of C. albicans. Δals1/Δals3 single and double deletion strains exhibited reduced fluorescence, indicating that probe binding required expression of these proteins. Additionally, the Als peptide specifically stained fungal cells in abscesses in autopsy sections. Counterstaining with calcofluor white showed colocalization with the amyloid peptide. In addition, fungi in autopsy sections derived from the gastrointestinal tract showed colocalization of the amyloid-specific dye thioflavin T and the fluorescent peptide. Collectively, our data demonstrate that we can exploit amyloid sequence specificity for detection of functional amyloids in situ.

Community interactions of oral streptococci

It is now clear that the most common oral diseases, dental caries and periodontitis, are caused by mixed-species communities rather than by individual pathogens working in isolation. Oral streptococci are central to these disease processes since they are frequently the first microorganisms to colonize oral surfaces and they are numerically the dominant microorganisms in the human mouth. Numerous interactions between oral streptococci and other bacteria have been documented. These are thought to be critical for the development of mixed-species oral microbial communities and for the transition from oral health to disease. Recent metagenomic studies are beginning to shed light on the co-occurrence patterns of streptococci with other oral bacteria. Refinements in microscopy techniques and biofilm models are providing detailed insights into the spatial distribution of streptococci in oral biofilms. Targeted genetic manipulation is increasingly being applied for the analysis of specific genes and networks that modulate interspecies interactions. From this work, it is clear that streptococci produce a range of extracellular factors that promote their integration into mixed-species communities and enable them to form social networks with neighboring taxa. These "community integration factors" include coaggregation-mediating adhesins and receptors, small signaling molecules such as peptides or autoinducer-2, bacteriocins, by-products of metabolism including hydrogen peroxide and lactic acid, and a range of extracellular enzymes. Here, we provide an overview of various types of community interactions between oral streptococci and other microorganisms, and we consider the possibilities for the development of new technologies to interfere with these interactions to help control oral biofilms.

Single-cell force spectroscopy of the medically important Staphylococcus epidermidis-Candida albicans interaction

Despite the clinical importance of bacterial-fungal interactions, their molecular details are poorly understood. A hallmark of such medically important interspecies associations is the interaction between the two nosocomial pathogens Staphylococcus aureus and Candida albicans, which can lead to mixed biofilm-associated infections with enhanced antibiotic resistance. Here, we use single-cell force spectroscopy (SCFS) to quantify the forces engaged in bacterial-fungal co-adhesion, focusing on the poorly investigated S. epidermidis-C. albicans interaction. Force curves recorded between single bacterial and fungal germ tubes showed large adhesion forces (~5 nN) with extended rupture lengths (up to 500 nm). By contrast, bacteria poorly adhered to yeast cells, emphasizing the important role of the yeast-to-hyphae transition in mediating adhesion to bacterial cells. Analysis of mutant strains altered in cell wall composition allowed us to distinguish the main fungal components involved in adhesion, i.e. Als proteins and O-mannosylations. We suggest that the measured co-adhesion forces are involved in the formation of mixed biofilms, thus possibly as well in promoting polymicrobial infections. In the future, we anticipate that this SCFS platform will be used in nanomedicine to decipher the molecular mechanisms of a wide variety of pathogen-pathogen interactions and may help in designing novel anti-adhesion agents.

Microbial interactions in building of communities

Establishment of a community is considered to be essential for microbial growth and survival in the human oral cavity. Biofilm communities have increased resilience to physical forces, antimicrobial agents and nutritional variations. Specific cell-to-cell adherence processes, mediated by adhesin-receptor pairings on respective microbial surfaces, are able to direct community development. These interactions co-localize species in mutually beneficial relationships, such as streptococci, veillonellae, Porphyromonas gingivalis and Candida albicans. In transition from the planktonic mode of growth to a biofilm community, microorganisms undergo major transcriptional and proteomic changes. These occur in response to sensing of diffusible signals, such as autoinducer molecules, and to contact with host tissues or other microbial cells. Underpinning many of these processes are intracellular phosphorylation events that regulate a large number of microbial interactions relevant to community formation and development.

Adhesins in human fungal pathogens: glue with plenty of stick

Understanding the pathogenesis of an infectious disease is critical for developing new methods to prevent infection and diagnose or cure disease. Adherence of microorganisms to host tissue is a prerequisite for tissue invasion and infection. Fungal cell wall adhesins involved in adherence to host tissue or abiotic medical devices are critical for colonization leading to invasion and damage of host tissue. Here, with a main focus on pathogenic Candida species, we summarize recent progress made in the field of adhesins in human fungal pathogens and underscore the importance of these proteins in establishment of fungal diseases.

Two unlike cousins: Candida albicans and C. glabrata infection strategies

Candida albicans and C. glabrata are the two most common pathogenic yeasts of humans, yet they are phylogenetically, genetically and phenotypically very different. In this review, we compare and contrast the strategies of C. albicans and C. glabrata to attach to and invade into the host, obtain nutrients and evade the host immune response. Although their strategies share some basic concepts, they differ greatly in their outcome. While C. albicans follows an aggressive strategy to subvert the host response and to obtain nutrients for its survival, C. glabrata seems to have evolved a strategy which is based on stealth, evasion and persistence, without causing severe damage in murine models. However, both fungi are successful as commensals and as pathogens of humans. Understanding these strategies will help in finding novel ways to fight Candida, and fungal infections in general.

Flexible survival strategies of Pseudomonas aeruginosa in biofilms result in increased fitness compared with Candida albicans

The majority of microorganisms persist in nature as surface-attached communities often surrounded by an extracellular matrix, called biofilms. Most natural biofilms are not formed by a single species but by multiple species. Microorganisms not only cooperate as in some multispecies biofilms but also compete for available nutrients. The Gram-negative bacterium Pseudomonas aeruginosa and the polymorphic fungus Candida albicans are two opportunistic pathogens that are often found coexisting in a human host. Several models of mixed biofilms have been reported for these organisms showing antagonistic behavior. To investigate the interaction of P. aeruginosa and C. albicans in more detail, we analyzed the secretome of single and mixed biofilms of both organisms using MALDI-TOF MS/MS at several time points. Overall 247 individual proteins were identified, 170 originated from P. aeruginosa and 77 from C. albicans. Only 39 of the 131 in mixed biofilms identified proteins were assigned to the fungus whereby the remaining 92 proteins belonged to P. aeruginosa. In single-species biofilms, both organisms showed a higher diversity of proteins with 73 being assigned to C. albicans and 154 to P. aeruginosa. Most interestingly, P. aeruginosa in the presence of C. albicans secreted 16 proteins in significantly higher amounts or exclusively among other virulence factors such as exotoxin A and iron acquisition systems. In addition, the high affinity iron-binding siderophore pyoverdine was identified in mixed biofilms but not in bacterial biofilms, indicating that P. aeruginosa increases its capability to sequester iron in competition with C. albicans. In contrast, C. albicans metabolism was significantly reduced, including a reduction in detectable iron acquisition proteins. The results obtained in this study show that microorganisms not only compete with the host for essential nutrients but also strongly with the present microflora in order to gain a competitive advantage.

Evaluation of adhesion forces of Staphylococcus aureus along the length of Candida albicans hyphae

Background

Candida albicans is a human fungal pathogen, able to cause both superficial and serious, systemic diseases and is able to switch from yeast cells to long, tube-like hyphae, depending on the prevailing environmental conditions. Both morphological forms of C. albicans are found in infected tissue, often in combination with Staphylococcus aureus. Although bacterial adhesion to the different morphologies of C. albicans has been amply studied, possible differences in staphylococcal adhesion forces along the length of C. albicans hyphae have never been determined. In this study, we aim to verify the hypothesis that the forces mediating S. aureus NCTC8325-4^GFP adhesion to hyphae vary along the length of C. albicans SC5314 and MB1 hyphae, as compared with adhesion to yeast cells.

Results

C. albicans hyphae were virtually divided into a “tip” (the growing and therefore youngest part of the hyphae), a “middle” and a so-called “head” region (the yeast cell from which germination started). Adhesion forces between S. aureus NCTC8325-4^GFP and the different regions of C. albicans SC5314 hyphae were measured using atomic force microscopy. Strong adhesion forces were found at the tip and middle regions of C. albicans hyphae (−4.1 nN and −4.0 nN, respectively), while much smaller adhesion forces were measured at the head region (−0.3 nN). Adhesion forces exerted by the head region were comparable with the forces arising from budding yeast cells (−0.5 nN). A similar regional dependence of the staphylococcal adhesion forces was found for the clinical isolate involved in this study, C. albicans MB1.

Conclusions

This is the first time that differences in adhesion forces between S. aureus and different regions of C. albicans hyphae have been demonstrated on a quantitative basis, supporting the view that the head region is different from the remainder of the hyphae. Notably it can be concluded that the properties of the hyphal head region are similar to those of budding yeast cells. These novel findings provide new insights in the intricate interkingdom interaction between C. albicans and S. aureus.

[Formation and quantification assay of Candida albicans and Staphylococcus aureus mixed biofilm]

This study quantifies the production of single and mixed biofilms of Candida albicans and Staphylococcus aureus to determine if such mixed biofilms have synergistic effects. Assays were performed using polystyrene microtitre plates of 96 wells, metabolic activity was measured by the enzymatic reduction of a tetrazolium salt (XTT) and colorimetric changes were measured at 490 nm. Confocal scanning laser microscopy was used to visualise the biofilms of each microorganism and its growth kinetics. The highest levels of biofilm formation were observed in mixed biofilms, followed by those of Candida albicans only, with the lowest levels of biofilm formation being detected for Staphylococcus aureus; all together these results suggest a synergistic relationship between the tested microorganisms.

Effects of salivary protein flow and indigenous microorganisms on initial colonization of Candida albicans in an in vivo model

BACKGROUND

Candida albicans is a dimorphic fungus that is part of the commensal microbial flora of the oral cavity. When the host immune defenses are impaired or when the normal microbial flora is disturbed, C. albicans triggers recurrent infections of the oral mucosa and tongue. Recently, we produced NOD/SCID.e2f1-/- mice that show hyposalivation, decrease of salivary protein flow, lack IgA and IgG in saliva, and have decreased NK cells. Our objective was to characterize C. albicans infection and biofilm formation in mice.

METHODS

NOD/SCID.e2f1-/- mice were used as an animal model for C. albicans infection. C. albicans yeast and hyphal forms solutions were introduced in the oral cavity after disinfection by Chlorhexidine.

RESULTS

The numbers of C. albicans colonized and decreased in a time-dependent manner in NOD/SCID.e2f1+/+ after inoculation. However, the colonization levels were higher in NOD/SCID.e2f1+/+ than NOD/SCID.e2f1-/- mice. In the mice fed 1% sucrose water before inoculation, C. albicans sample was highly contaminated by indigenous microorganisms in the oral cavity; and was not in the mice fed no sucrose water. The colonization of C. albicans was not influenced by the contamination of indigenous microorganisms. The hyphal form of C. albicans restricted the restoration of indigenous microorganisms. The decreased saliva in NOD/SCID.e2f1-/- did not increase the colonization of C. albicans in comparison to NOD/SCID.e2f1+/+ mice. We suggest that the receptor in saliva to C. albicans may not be sufficiently provided in the oral cavity of NOD/SCID.e2f1-/- mice.

CONCLUSION

The saliva protein flow may be very important for C. albicans initial colonization, where the indigenous microorganisms do not affect colonization in the oral cavity.

Staphylococcus aureus adherence to Candida albicans hyphae is mediated by the hyphal adhesin Als3p

The bacterium Staphylococcus (St.) aureus and the opportunistic fungus Candida albicans are currently among the leading nosocomial pathogens, often co-infecting critically ill patients, with high morbidity and mortality. Previous investigations have demonstrated preferential adherence of St. aureus to C. albicans hyphae during mixed biofilm growth. In this study, we aimed to characterize the mechanism behind this observed interaction. C. albicans adhesin-deficient mutant strains were screened by microscopy to identify the specific receptor on C. albicans hyphae recognized by St. aureus. Furthermore, an immunoassay was developed to validate and quantify staphylococcal binding to fungal biofilms. The findings from these experiments implicated the C. albicans adhesin agglutinin-like sequence 3 (Als3p) in playing a major role in the adherence process. This association was quantitatively established using atomic force microscopy, in which the adhesion force between single cells of the two species was significantly reduced for a C. albicans mutant strain lacking als3. Confocal microscopy further confirmed these observations, as St. aureus overlaid with a purified recombinant Als3 N-terminal domain fragment (rAls3p) exhibited robust binding. Importantly, a strain of Saccharomyces cerevisiae heterologously expressing Als3p was utilized to further confirm this adhesin as a receptor for St. aureus. Although the parental strain does not bind bacteria, expression of Als3p on the cell surface conferred upon the yeast the ability to strongly bind St. aureus. To elucidate the implications of these in vitro findings in a clinically relevant setting, an ex vivo murine model of co-infection was designed using murine tongue explants. Fluorescent microscopic images revealed extensive hyphal penetration of the epithelium typical of C. albicans mucosal infection. Interestingly, St. aureus bacterial cells were only seen within the epithelial tissue when associated with the invasive hyphae. This differed from tongues infected with St. aureus alone or in conjunction with the als3 mutant strain of C. albicans, where bacterial presence was limited to the outer layers of the oral tissue. Collectively, the findings generated from this study identified a key role for C. albicans Als3p in mediating this clinically relevant fungal-bacterial interaction.

Removal of Biofilms from Tracheoesophageal Speech Valves Using a Novel Marine Microbial Deoxyribonuclease

Objective

The growth of biofilms on tracheoesophageal speech valves shortens their life span and produces a reservoir of pathogens that may infect the respiratory tract. The authors have discovered a novel nontoxic deoxyribonuclease, NucB, from a marine isolate of Bacillus licheniformis that is effective at dispersing a variety of mono and mixed-species bacterial biofilms. The aim of this preliminary study was to determine whether NucB could also disrupt and remove mixed-species biofilms from tracheoesophageal speech valves.

Study Design

Laboratory-based treatment and analysis of discarded tracheoesophageal speech valves.

Setting

University human biology laboratory and the Department of Speech and Language Therapy at a tertiary referral hospital.

Subjects and Methods

Seventeen ex vivo tracheoesophageal speech valves fouled with natural human biofilms were collected and divided into 2 equal parts. One half was treated with NucB and the other half with a control buffer solution. Biofilm removal was measured by microscopy and by culture of dispersed biofilm organisms on agar plates.

Results

Significantly more organisms were released from biofilms using NucB than with buffer solution alone. On nonselective medium, more organisms were cultured in 11 samples (65%, n = 17, P < .05). Using growth media favoring fungi, more organisms were cultured in 14 samples (82%, n = 17, P < .05).

Conclusion

The nontoxic deoxyribonuclease NucB was effective in releasing more microorganisms from biofilms on tracheoesophageal speech valves. This reflects its potential ability to break up and disperse these biofilms. Future studies will aim to develop NucB as a novel agent to prolong the life span of tracheoesophageal speech valves, thus reducing health care costs.

Polymicrobial interactions: impact on pathogenesis and human disease

Microorganisms coexist in a complex milieu of bacteria, fungi, archaea, and viruses on or within the human body, often as multifaceted polymicrobial biofilm communities at mucosal sites and on abiotic surfaces. Only recently have we begun to appreciate the complicated biofilm phenotype during infection; moreover, even less is known about the interactions that occur between microorganisms during polymicrobial growth and their implications in human disease. Therefore, this review focuses on polymicrobial biofilm-mediated infections and examines the contribution of bacterial-bacterial, bacterial-fungal, and bacterial-viral interactions during human infection and potential strategies for protection against such diseases.