A customizable and defined medium supporting culturing of Candida albicans, Staphylococcus aureus, and human oral epithelial cells.

Candida albicans, an opportunistic oral pathogen, synergizes with Staphylococcus aureus, allowing bacteria to co-invade and systemically disseminate within the host. Studying human-microbe interactions creates the need for a universal culture medium that supports fungal, bacterial, and human cell culturing, while allowing sensitive analytical approaches such as OMICs and chromatography techniques. In this study, we established a fully defined, customizable adaptation of Dulbecco's modified Eagle medium (DMEM), allowing multi-kingdom culturing of S. aureus, C. albicans, and human oral cell lines, whereas minimal version of DMEM (mDMEM) did not support growth of S. aureus, and neither did supplementation with dextrose, MEM non-essential amino acids, pyruvate, and Glutamax. This new medium composition, designated as "mDMEM-DMP," promoted growth of all tested S. aureus strains. Addition of 25 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) further improved growth, while higher concentrations did not improve growth any further. Higher concentrations of HEPES did result in prolonged stabilization of medium pH. mDMEM-DMP promoted (hyphal) C. albicans monoculturing and co-culturing on both solid and semi-solid surfaces. In contrast to S. aureus, addition of HEPES reduced C. albicans maximum culture optical density (OD). Finally, only buffered mDMEM-DMP (100 mM HEPES) was successful in maintaining the metabolic activity of human oral Ca9-22 and HO1N1 cell lines for 24 hours. Altogether, our findings show that mDMEM-DMP is a versatile and potent culture medium for both microbial and human cell culturing, providing a customizable platform to study human as well as microbial molecular physiology and putative interactions. IMPORTANCE: Interaction between microbes and the host are in the center of interest both in disease and in health. In order to study the interactions between microbes of different kingdoms and the host, alternative media are required. Synthetic media are useful as they allow addition of specific components. In addition, well-defined media are required if high-resolution analyses such as metabolomics and proteomics are desired. We describe the development of a synthetic medium to study the interactions between C. albicans, S. aureus, and human oral epithelial cells. Our findings show that mDMEM-DMP is a versatile and potent culture medium for both microbial and human cell culturing, providing a customizable platform to study human as well as microbial molecular physiology and putative interactions.

Immunoediting role for major vault protein in apoptotic signaling induced by bacterial N-acyl homoserine lactones.

The major vault protein (MVP) mediates diverse cellular responses, including cancer cell resistance to chemotherapy and protection against inflammatory responses to Pseudomonas aeruginosa Here, we report the use of photoactive probes to identify MVP as a target of the N-(3-oxo-dodecanoyl) homoserine lactone (C12), a quorum sensing signal of certain proteobacteria including P. aeruginosa. A treatment of normal and cancer cells with C12 or other N-acyl homoserine lactones (AHLs) results in rapid translocation of MVP into lipid raft (LR) membrane fractions. Like AHLs, inflammatory stimuli also induce LR-localization of MVP, but the C12 stimulation reprograms (functionalizes) bioactivity of the plasma membrane by recruiting death receptors, their apoptotic adaptors, and caspase-8 into LR. These functionalized membranes control AHL-induced signaling processes, in that MVP adjusts the protein kinase p38 pathway to attenuate programmed cell death. Since MVP is the structural core of large particles termed vaults, our findings suggest a mechanism in which MVP vaults act as sentinels that fine-tune inflammation-activated processes such as apoptotic signaling mediated by immunosurveillance cytokines including tumor necrosis factor-related apoptosis inducing ligand (TRAIL).

Oral host-microbe interactions investigated in 3D organotypic models.

The oral cavity is inhabited by abundant microbes which continuously interact with the host and influence the host's health. Such host-microbe interactions (HMI) are dynamic and complex processes involving e.g. oral tissues, microbial communities and saliva. Due to difficulties in mimicking the in vivo complexity, it is still unclear how exactly HMI influence the transition between healthy status and disease conditions in the oral cavity. As an advanced approach, three-dimensional (3D) organotypic oral tissues (epithelium and mucosa/gingiva) are being increasingly used to study underlying mechanisms. These in vitro models were designed with different complexity depending on the research questions to be answered. In this review, we summarised the existing 3D oral HMI models, comparing designs and readouts, discussing applications as well as future perspectives.

The novel endolysin XZ.700 effectively treats MRSA biofilms in two biofilm models without showing toxicity on human bone cells in vitro.

In this in vitro study the effect of XZ.700, a new endolysin, on methicillin resistant Staphylococcus aureus (MRSA) biofilms grown on titanium was evaluated. Biofilms of S. aureus USA300 were grown statically and under flow, and treatment with XZ.700 was compared with povidone-iodine (PVP-I) and gentamicin. To evaluate the cytotoxic effects of XZ.700 and derived biofilm lysates, human osteocyte-like cells were exposed to biofilm supernatants, and metabolism and proliferation were quantified. XZ.700 showed a significant, concentration dependent reduction in biofilm viability, compared with carrier controls. Metabolism and proliferation of human osteocyte-like cells were not affected by XZ.700 or lysates, unlike PVP-I and gentamicin lysates which significantly inhibited proliferation. Using time-lapse microscopy, rapid biofilm killing and removal was observed for XZ.700. In comparison, PVP-I and gentamicin showed slower biofilm killing, with no apparent biofilm removal. In conclusion, XZ.700 reduced MRSA biofilms, especially under flow condition, without toxicity for surrounding bone cells.

Short-Chain N-Acylhomoserine Lactone Quorum-Sensing Molecules Promote Periodontal Pathogens in In Vitro Oral Biofilms.

Acylhomoserine lactones (AHLs), the quorum-sensing (QS) signals produced by a range of Gram-negative bacteria, are involved in biofilm formation in many pathogenic and environmental bacteria. Nevertheless, the current paradigm excludes a role of AHLs in dental plaque formation, while other QS signals, such as AI-2 and autoinducer peptides, have been demonstrated to play an important role in biofilm formation and virulence-related gene expression in oral pathogens. In the present work, we have explored the effect of externally added AHLs on in vitro oral biofilm models for commensal, cariogenic, and periodontal dental plaque. While little effect on bacterial growth was observed, some AHLs specifically affected the lactic acid production and protease activity of the biofilms. Most importantly, the analysis of bacterial diversity in the biofilms showed that the addition of C6-homoserine lactone (C6-HSL) results in a shift toward a periodontal bacterial composition profile by increasing the relative presence of the orange-complex bacteria Peptostreptococcus and Prevotella These results point to a relevant role of AHL-mediated QS in dental plaque formation and might be involved in the development of dysbiosis, the mechanism of which should be further investigated. This finding potentially opens new opportunities for the prevention or treatment of the periodontal disease.IMPORTANCE Dental plaque is omnipresent in healthy oral cavities and part of our commensal microbial colonization. At the same time, dental plaque is the cause of the most common human diseases, caries and gum disease. Dental plaque consists of billions of microbes attached to the surface of your teeth. Communication among these microbes is pivotal for development of these complex communities yet poorly studied in dental plaque. In the present study, we show that a specific communication molecule induces changes within the community related to the development of gum disease. This finding suggests that interfering with microbial communication may represent an interesting novel strategy to prevent gum disease that should be further investigated.

DNase-mediated eDNA removal enhances D-LL-31 activity against biofilms of bacteria isolated from chronic rhinosinusitis patients.

Chronic rhinosinusitis (CRS) is a chronic infection of the nasal cavity and paranasal sinuses associated with the presence of a microbial biofilm. Extracellular DNA (eDNA) is an important component of the biofilm matrix. Antimicrobial peptides (AMPs) are natural peptides with the ability to kill microorganisms. D-LL-31 is a synthetic variant of the AMP cathelicidin with increased resistance to proteolytic breakdown. In this study it is shown for 3 clinical CRS isolates that treatment of 24 h biofilms with DNase I enhanced the antimicrobial activity of D-LL-31. Conversely, co-incubation of D-LL-31 at the IC50 value with exogenous DNA resulted in reduced antimicrobial activity. DNase I alone did not show antimicrobial activity against the isolates tested but caused dispersal of an established biofilm. Hence, the presence of eDNA in the biofilm matrix reduced AMP-mediated killing. These results suggest that combination therapy with proteolysis resistant AMP D-LL-31 and DNase could be considered for effective treatment of CRS.

The Host Immune System Facilitates Disseminated Staphylococcus aureus Disease Due to Phagocytic Attraction to Candida albicans during Coinfection: a Case of Bait and Switch.

Invasive Staphylococcus aureus infections account for 15 to 50% of fatal bloodstream infections annually. These disseminated infections often arise without a defined portal of entry into the host but cause high rates of mortality. The fungus Candida albicans and the Gram-positive bacterium S. aureus can form polymicrobial biofilms on epithelial tissue, facilitated by the C. albicans adhesin encoded by ALS3 While a bacterium-fungus interaction is required for systemic infection, the mechanism by which bacteria disseminate from the epithelium to internal organs is unclear. In this study, we show that highly immunogenic C. albicans hyphae attract phagocytic cells, which rapidly engulf adherent S. aureus and subsequently migrate to cervical lymph nodes. Following S. aureus-loaded phagocyte translocation from the mucosal surface, S. aureus produces systemic disease with accompanying morbidity and mortality. Our results suggest a novel role for the host in facilitating a bacterium-fungus infectious synergy, leading to disseminated staphylococcal disease.

Candida albicans enhances initial biofilm growth of Cutibacterium acnes under aerobic conditions.

Candida albicans and Cutibacterium acnes are opportunistic pathogens that co-colonize the human body. They are involved in biofilm-related infections of implanted medical devices. The objective of this study was to evaluate the ability of these species to interact and form polymicrobial biofilms. SEM imaging and adhesion assays showed that C. acnes adhesion to C. albicans did not have a preference for a specific morphological state of C. albicans; bacteria adhered to both hyphal and yeast forms of C. albicans. C. albicans did not influence growth of C. acnes under anaerobic growth conditions, however under aerobic growth condition, C. albicans enhanced early C. acnes biofilm formation. This favorable impact of C. albicans was not mediated by secreted compounds accumulating in the medium, but required the presence of metabolically active C. albicans. The ability of these microorganisms to interact together could modulate the physiopathology of infections.

Review: modulation of the oral microbiome by the host to promote ecological balance.

The indivisible relationship between the human host and its oral microbiome has been shaped throughout the millennia, by facing various changes that have forced the adaptation of oral microorganisms to new environmental conditions. In this constant crosstalk between the human host and its microbiome, a bidirectional relationship has been established. The microorganisms provide the host with functions it cannot perform on its own and at the same time the host provides its microbes with a suitable environment for their growth and development. These host factors can positively affect the microbiome, promoting diversity and balance between different species, resulting in a state of symbiosis and absence of pathology. In contrast, other host factors can negatively influence the composition of the oral microbiome and drive the interaction towards a dysbiotic state, where the balance tilts towards a harmful relationship between the host and its microbiome. The aim of this review is to describe the role host factors play in cultivating and maintaining a healthy oral ecology and discuss mechanisms that can prevent its drift towards dysbiosis.

Phytosphingosine Prevents the Formation of Young Salivary Biofilms in vitro.

Dental biofilms are formed in a multistep process that is initiated by the adhesion of oral bacteria to the dental hard surface. As dental biofilms are associated with oral diseases their control is necessary in order to maintain oral health. Recently, it was revealed that phytosphingosine (PHS)-treated hydroxyapatite discs showed anti-adhesive activity in a static in vitro biofilm model against Streptococcus mutans. The goal of the present study was to further unravel the anti-adhesive and anti-biofilm properties of PHS in both static and dynamic in vitro biofilm models against a full salivary inoculum. After 3 h under static conditions, bacterial adherence on PHS-treated cover glass slides was reduced by 60% compared to the untreated surface. After 6 and 24 h under static conditions, no significant differences in bacterial adherence were observed between PHS-treated and untreated cover glass slides. However, under dynamic conditions, i.e., the presence of shear forces, virtually no bacterial adherence was observed for up to 16 h on PHS-coated surfaces. Besides, PHS showed a strong bactericidal activity on salivary biofilms. Treatment of a 3- and 6-h statically grown biofilm resulted in a 99 and 94% reduction of viable cells, respectively, which was effectuated within minutes. In principle, these anti-adherence and anti-biofilm properties make PHS a promising candidate ingredient for use in oral care products aimed at oral microbial control.

Fungal mitochondrial oxygen consumption induces the growth of strict anaerobic bacteria.

Fungi are commonly encountered as part of a healthy oral ecosystem. Candida albicans is the most often observed and investigated fungal species in the oral cavity. The role of fungi in the oral ecosystem has remained enigmatic for decades. Recently, it was shown that C. albicans, in vitro, influences the bacterial composition of young oral biofilms, indicating it possibly plays a role in increasing diversity in the oral ecosystem. C. albicans favored growth of strictly anaerobic species under aerobic culture conditions. In the present study, the role of mitochondrial respiration, as mechanism by which C. albicans modifies its environment, was investigated. Using oxygen sensors, a rapid depletion of dissolved oxygen (dO2) was observed. This decrease was not C. albicans specific as several non-albicans Candida species showed similar oxygen consumption. Heat inactivation as well as addition of the specific mitochondrial respiration inhibitor Antimycin A inhibited depletion of dO2. Using 16S rDNA sequencing, it is shown that mitochondrial activity, more than physical presence of C. albicans is responsible for inducing growth of strictly anaerobic oral bacteria in aerobic growth conditions. The described mechanism of dO2 depletion may be a general mechanism by which fungi modulate their direct environment.

Ica-status of clinical Staphylococcus epidermidis strains affects adhesion and aggregation: a thermodynamic analysis.

Staphylococcus epidermidis is a major nosocomial pathogen associated with infections of indwelling medical devices. One important virulence factor of these organisms is their ability to adhere to devices and form biofilms. In this study, we evaluated the effect of the ica operon on cell surface hydrophobicity, thermodynamics of adhesion, and biofilm formation for seven S. epidermidis strains. The surface free energy parameters of the bacterial cell surface and the substratum were determined by contact angle measurement. Biofilm formation was assayed using crystal violet staining. Results showed that ica-positive strains demonstrated a higher hydrophobic characteristic than ica-negative strains, suggesting that the ica-operon seems to determine the cell surface hydrophobicity of S. epidermidis. Interaction of ica-positive strains with a tissue-culture treated polystyrene surface was energetically favourable (ΔGTot < 0), in contrast to ica-negative strains (ΔGTot > 0). The interfacial free energy of aggregation of S. epidermidis was lower for ica-positive than for ica-negative strains. Our study suggests that, in addition to biofilm formation, adhesion and aggregation of clinical S. epidermidis is stimulated in ica-positive strains by influencing the thermodynamics of interaction.

The mycobiome of root canal infections is correlated to the bacteriome.

OBJECTIVES: Bacterial infection of the root canal system causes apical periodontitis. Less is known about the role of fungi in these infections. This study aimed to assess the fungal prevalence, abundance, and diversity of root canal infections, as well as the relation between fungi and bacteria present in different parts of the root canal. MATERIALS AND METHODS: Twenty-six teeth with primary apical periodontitis were extracted, split in apical and coronal root segments, and cryo-pulverized. Bacteriome profiles of 23 teeth were analyzed based on the V3-V4 hypervariable region of the 16S ribosomal RNA gene. Mycobiome profiles of six teeth were analyzed based on the internal transcribed spacer (ITS) 1 or ITS2 region. Samples were sequenced on the Illumina MiSeq platform. RESULTS: A total of 338 bacterial operational taxonomic units (OTUs), 28 ITS1 OTUs, and 24 ITS2 OTUs were identified. Candida and Malassezia were the most frequently identified fungi. No differences could be found between the bacteriome and mycobiome profiles of the apical and coronal root segments. The bacteriome of fungi-positive root segments contained more Actinomyces, Bifidobacterium, four different Lactobacillus OTUs, Propionibacterium, and Streptococcus. A Spearman correlation matrix between bacteriomes and mycobiomes identified no correlations, but separate clusters could be observed. CONCLUSIONS: A considerable proportion of the root canal infections contain fungi, although fungal diversity is limited. However, when fungi are present, the composition of the bacteriome is clearly different. CLINICAL RELEVANCE: Interaction between bacteria and fungi in root canal infections may complicate the infection and require alternative treatment strategies.

Fine-Tuning Covalent Inhibition of Bacterial Quorum Sensing.

Emerging antibiotic resistance among human pathogens has galvanized efforts to find alternative routes to combat bacterial virulence. One new approach entails interfering with the ability of bacteria to coordinate population-wide gene expression, or quorum sensing (QS), thus inhibiting the production of virulence factors and biofilm formation. We have recently developed such a strategy by targeting LasR, the master regulator of QS in the opportunistic human pathogen Pseudomonas aeruginosa, through the rational design of covalent inhibitors closely based on the core structure of the native ligand. We now report several groups of new inhibitors, one of which, fluoro-substituted ITC-12, displayed complete covalent modification of LasR, as well as effective QS inhibition in vitro and promising in vivo results. In addition to their potential clinical relevance, this series of synthetic QS modulators can be used as a tool to further unravel the complicated QS regulation in P. aeruginosa.

Candida albicans in Multispecies Oral Communities; A Keystone Commensal?

The complexity of the oral cavity, in which many hundreds of microbial species interact represents a challenge for modern microbiologists. What are all these species doing there? And why do we accept so many opportunistic pathogens to be part of our health (commensal) microflora? While the role of bacteria are often being studied, the role of fungi in the interactions within the oral cavity are understudied. This is partly because fungi in the oral cavity are generally considered as pathogens and related to diseases. In this chapter we will explore mechanisms of interaction between bacteria and fungi in the oral cavity that are involved in maintenance of oral health. We will argue that fungi in general and C. albicans specifically, should be regarded a keystone commensal in the oral cavity.

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.

In vitro phenotypic differentiation towards commensal and pathogenic oral biofilms.

Commensal oral biofilms, defined by the absence of pathology-related phenotypes, are ubiquitously present. In contrast to pathological biofilms commensal biofilms are rarely studied. Here, the effect of the initial inoculum and subsequent growth conditions on in vitro oral biofilms was studied. Biofilms were inoculated with saliva and grown anaerobically for up to 21 days in McBain medium with or without fetal calf serum (FCS) or sucrose. Pathology-related phenotypes were quantified and the community composition was determined. Biofilms inoculated with pooled saliva or individual inocula were similar. Denaturing gradient gel electrophoresis (DGGE) analysis allowed differentiation of biofilms grown with sucrose, but not with FCS. Lactate production by biofilms was significantly increased by sucrose and protease activity by FCS. McBain grown biofilms showed low activity for both phenotypes. Three clinically relevant in vitro biofilm models were developed and could be differentiated based on pathology-related phenotypes but not DGGE analysis. These models allow analysis of health-to-disease shifts and the effectiveness of prevention measures.

LuxS signaling in Porphyromonas gingivalis-host interactions.

Dental plaque is a multispecies biofilm in the oral cavity that significantly influences oral health. The presence of the oral anaerobic pathogen Porphyromonas gingivalis is an important determinant in the development of periodontitis. Direct and indirect interactions between P. gingivalis and the host play a major role in disease development. Transcriptome analysis recently revealed that P. gingivalis gene-expression is regulated by LuxS in both an AI-2-dependent and an AI-2 independent manner. However, little is known about the role of LuxS-signaling in P. gingivalis-host interactions. Here, we investigated the effect of a luxS mutation on the ability of P. gingivalis to induce an inflammatory response in human oral cells in vitro. Primary periodontal ligament (PDL) fibroblasts were challenged with P. gingivalis ΔluxS or the wild-type parental strain and gene-expression of pro-inflammatory mediators IL-1ß, IL-6 and MCP-1 was determined by real-time PCR. The ability of P. gingivalis ΔluxS to induce an inflammatory response was severely impaired in PDL-fibroblasts. This phenotype could be restored by providing of LuxS in trans, but not by addition of the AI-2 precursor DPD. A similar phenomenon was observed in a previous transcriptome study showing that expression of PGN_0482 was reduced in the luxS mutant independently of AI-2. We therefore also analyzed the effect of a mutation in PGN_0482, which encodes an immuno-reactive, putative outer-membrane protein. Similar to P. gingivalis ΔluxS, the P. gingivalis Δ0482 mutant had an impaired ability to induce an inflammatory response in PDL fibroblasts. LuxS thus appears to influence the pro-inflammatory responses of host cells to P. gingivalis, likely through regulation of PGN_0482.

Design and evaluation of an immunology and pathology course that is tailored to today's dentistry students.

Curricular reform provides new opportunities to renovate important pillars of the dentistry curriculum, such as immunology and pathology, with novel approaches that appeal to new generations of students. When redesigning a course that integrates both immunology and pathology at the level that provides dentistry students with sustainable knowledge that is useful for their entire career, several challenges must be met. The objective of the present study was to describe the considerations involved in the design phase of such a new course. First, the course should be compatible with the new view on the incorporation of more active learning and teaching methods. Practically, this means that the course design should contain fewer lectures and more seminars and tutorials, where the students have fewer contact hours and actively engage in using recently acquired knowledge within a contextual background. A mandatory session of team-based learning provides opportunities to apply knowledge in combination with academic reasoning skills, teamwork, and communication. Second, for a 4-week course, choices must be made: students will not become immunologists nor pathologists in such a short period. A governing principle for this course's design is that it should be based on understanding the basic principles of immunology and pathology. The ultimate goal for the students is to make the course immuno-logical and patho-logical, challenging them to reach a next level but clearly without oversimplification. Part of the course design should allow room for students to further study an immunological topic of their own choice, thereby contributing to their immunological curiosity and to their academic development. Third, to make it tailored to a new generation of dentists, examples from the field of dentistry are actively integrated in all aspects of the course. Finally, the era of ChatGPT provides novel opportunities to use generative artificial intelligence (AI) tools in the learning process, but it demands critical thinking of how to use it in a newly designed course. A mid-course evaluation revealed that students acknowledged that immunology and pathology were presented as an integrated course. The final course evaluation endorsed the use of these various educational methods. These methods proved to be appropriate and logical choices for reaching the learning goals of the course.

Porphyromonas gingivalis interaction with Candida albicans allows for aerobic escape, virulence and adherence.

In the oral cavity Candida albicans interacts with many oral bacteria, including Porphyromonas gingivalis, both physically and metabolically. The aim of this in vitro study was to characterize these interactions and study their effects on the survival of P. gingivalis. First, metabolic interactions were evaluated by counting the colony forming units (CFU) after co-culturing. The results indicated that the anaerobic bacterium P. gingivalis survives under aerobic conditions when co-cultured with C. albicans. This is due to the oxygen consumption by C. albicans as determined by a reduction in survival upon the addition of Antimycin A. By measuring the protease activity, it was found that the presence of C. albicans induced gingipain activity by P. gingivalis, which is an important virulence factor. Adherence of P. gingivalis to hyphae of C. albicans was observed with a dynamic flow system. Using various C. albicans mutants, it was shown that the mechanism of adhesion was mediated by the cell wall adhesins, members of the agglutinin-like sequence (Als) family: Als3 and Als1. Furthermore, the two microorganisms could be co-cultured into forming a biofilm in which P. gingivalis can survive under aerobic culturing conditions, which was imaged using scanning electron microscopy. This study has further elucidated mechanisms of interaction, virulence acquisition and survival of P. gingivalis when co-cultured with C. albicans. Such survival could be essential for the pathogenicity of P. gingivalis in the oxygen-rich niches of the oral cavity. This study has emphasized the importance of interaction between different microbes in promoting survival, virulence and attachment of pathogens, which could be essential in facilitating penetration into the environment of the host.