Coaggregation of Candida albicans with oral Fusobacterium species

New Electron-Transfer Chain to a Flavodiiron Protein in Fusobacterium nucleatum Couples Butyryl-CoA Oxidation to O2 Reduction

Fusobacterium nucleatum, a Gram-negative obligate anaerobe, is common to the oral microbiota, but the species is known to infect other sites of the body where it is associated with a range of pathologies. At present, little is known about the mechanisms by which F. nucleatum mitigates against oxidative and nitrosative stress. Inspection of the F. nucleatum subsp. polymorphum ATCC 10953 genome reveals that it encodes a flavodiiron protein (FDP; FNP2073) that is known in other organisms to reduce NO to N2O and/or O2 to H2O. FNP2073 is dicistronic with a gene encoding a multicomponent enzyme termed BCR for butyryl-CoA reductase. BCR is composed of a butyryl-CoA dehydrogenase domain (BCD), the C-terminal domain of the α-subunit of the electron-transfer flavoprotein (Etfα), and a rubredoxin domain. We show that BCR and the FDP form an α4β4 heterotetramic complex and use butyryl-CoA to selectively reduce O2 to H2O. The FAD associated with the Etfα domain (α-FAD) forms red anionic semiquinone (FAD•-), whereas the FAD present in the BCD domain (δ-FAD) forms the blue-neutral semiquinone (FADH•), indicating that both cofactors participate in one-electron transfers. This was confirmed in stopped-flow studies where the reduction of oxidized BCR with an excess of butyryl-CoA resulted in rapid (<1.6 ms) interflavin electron transfer evidenced by the formation of the FAD•-. Analysis of bacterial genomes revealed that the dicistron is present in obligate anaerobic gut bacteria considered to be beneficial by virtue of their ability to produce butyrate. Thus, BCR-FDP may help to maintain anaerobiosis in the colon.

Neglected gut microbiome: interactions of the non-bacterial gut microbiota with enteric pathogens

A diverse array of commensal microorganisms inhabits the human intestinal tract. The most abundant and most studied members of this microbial community are undoubtedly bacteria. Their important role in gut physiology, defense against pathogens, and immune system education has been well documented over the last decades. However, the gut microbiome is not restricted to bacteria. It encompasses the entire breadth of microbial life: viruses, archaea, fungi, protists, and parasitic worms can also be found in the gut. While less studied than bacteria, their divergent but important roles during health and disease have become increasingly more appreciated. This review focuses on these understudied members of the gut microbiome. We will detail the composition and development of these microbial communities and will specifically highlight their functional interactions with enteric pathogens, such as species of the family Enterobacteriaceae. The interactions can be direct through physical interactions, or indirect through secreted metabolites or modulation of the immune response. We will present general concepts and specific examples of how non-bacterial gut communities modulate bacterial pathogenesis and present an outlook for future gut microbiome research that includes these communities.

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

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

Fungal diseases: Oral dysbiosis in susceptible hosts

The oral cavity is colonized by a large number of microorganisms that are referred to collectively as the oral microbiota. These indigenous microorganisms have evolved in symbiotic relationships with the oral mucosal immune system and are involved in maintaining homeostasis in the oral cavity. Although Candida species are commonly found in the healthy oral cavity without causing infection, these fungi can become pathogenic. Recents advances indicate that the development of oral candidiasis is driven both by Candida albicans overgrowth in a dysbiotic microbiome and by disturbances in the host's immune system. Perturbation of the oral microbiota triggered by host-extrinsic (ie, medications), host-intrinsic (ie, host genetics), and microbiome-intrinsic (ie, microbial interactions) factors may increase the risk of oral candidiasis. In this review, we provide an overview of the oral mycobiome, with a particular focus on the interactions of Candida albicans with some of the most common oral bacteria and the oral mucosal immune system. Also, we present a summary of our current knowledge of the host-intrinsic and host-extrinsic factors that can predispose to oral candidiasis.

Genetic and molecular determinants of polymicrobial interactions in Fusobacterium nucleatum

A gram-negative colonizer of the oral cavity, Fusobacterium nucleatum not only interacts with many pathogens in the oral microbiome but also has the ability to spread to extraoral sites including placenta and amniotic fluid, promoting preterm birth. To date, however, the molecular mechanism of interspecies interactions-termed coaggregation-by F. nucleatum and how coaggregation affects bacterial virulence remain poorly defined. Here, we employed genome-wide transposon mutagenesis to uncover fusobacterial coaggregation factors, revealing the intertwined function of a two-component signal transduction system (TCS), named CarRS, and a lysine metabolic pathway in regulating the critical coaggregation factor RadD. Transcriptome analysis shows that CarR modulates a large regulon including radD and lysine metabolic genes, such as kamA and kamD, the expression of which are highly up-regulated in the ΔcarR mutant. Significantly, the native culture medium of ΔkamA or ΔkamD mutants builds up abundant amounts of free lysine, which blocks fusobacterial coaggregation with streptococci. Our demonstration that lysine-conjugated beads trap RadD from the membrane lysates suggests that lysine utilizes RadD as its receptor to act as a metabolic inhibitor of coaggregation. Lastly, using a mouse model of preterm birth, we show that fusobacterial virulence is significantly attenuated with the ΔkamA and ΔcarR mutants, in contrast to the enhanced virulence phenotype observed upon diminishing RadD (ΔradD or ΔcarS mutant). Evidently, F. nucleatum employs the TCS CarRS and environmental lysine to modulate RadD-mediated interspecies interaction, virulence, and nutrient acquisition to thrive in the adverse environment of oral biofilms and extraoral sites.

Genetic Manipulation and Virulence Assessment of Fusobacterium nucleatum

Considered a commensal, the Gram-negative anaerobe Fusobacterium nucleatum is a key member of the oral microbiome due to its wide range of interactions with many oral microbes. While the periodontal pathogenic properties of this organism have widely been examined, its connotation with extra-oral infections, including preterm birth and colorectal cancer, has now become apparent. Nonetheless, little is known about the mechanisms of pathogenicity and the associated virulence factors of F. nucleatum, most likely due to limited genetic tools and facile methodology. Here, we describe molecular techniques for the genetic manipulation of F. nucleatum, including markerless, nonpolar gene deletion, complementation, and Tn5 transposon mutagenesis. Further, we provide methodology to assess virulence potential of F. nucleatum using a mouse model of preterm birth. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Generation of a galK mutant strain Basic Protocol 2: Complementation of a mutant strain Basic Protocol 3: Tn5 transposon mutagenesis of F. nucleatum Basic Protocol 4: Mouse model of preterm birth.

Crossing Kingdoms: How the Mycobiota and Fungal-Bacterial Interactions Impact Host Health and Disease

The term “microbiota” invokes images of mucosal surfaces densely populated with bacteria. These surfaces and the luminal compartments they form indeed predominantly harbor bacteria.

The term “microbiota” invokes images of mucosal surfaces densely populated with bacteria. These surfaces and the luminal compartments they form indeed predominantly harbor bacteria. However, research from this past decade has started to complete the picture by focusing on important but largely neglected constituents of the microbiota: fungi, viruses, and archaea. The community of commensal fungi, also called the mycobiota, interacts with commensal bacteria and the host. It is thus not surprising that changes in the mycobiota have significant impact on host health and are associated with pathological conditions such as inflammatory bowel disease (IBD). In this review we will give an overview of why the mycobiota is an important research area and different mycobiota research tools. We will specifically focus on distinguishing transient and actively colonizing fungi of the oral and gut mycobiota and their roles in health and disease. In addition to correlative and observational studies, we will discuss mechanistic studies on specific cross-kingdom interactions of fungi, bacteria, and the host.

Maintaining homeostatic control of periodontal bone tissue

Alveolar bone is a unique osseous tissue due to the proximity of dental plaque biofilms. Periodontal health and homeostasis are mediated by a balanced host immune response to these polymicrobial biofilms. Dysbiotic shifts within dental plaque biofilms can drive a proinflammatory immune response state in the periodontal epithelial and gingival connective tissues, which leads to paracrine signaling to subjacent bone cells. Sustained chronic periodontal inflammation disrupts "coupled" osteoclast-osteoblast actions, which ultimately result in alveolar bone destruction. This chapter will provide an overview of alveolar bone physiology and will highlight why the oral microbiota is a critical regulator of alveolar bone remodeling. The ecology of dental plaque biofilms will be discussed in the context that periodontitis is a polymicrobial disruption of host homeostasis. The pathogenesis of periodontal bone loss will be explained from both a historical and current perspective, providing the opportunity to revisit the role of fibrosis in alveolar bone destruction. Periodontal immune cell interactions with bone cells will be reviewed based on our current understanding of osteoimmunological mechanisms influencing alveolar bone remodeling. Lastly, probiotic and prebiotic interventions in the oral microbiota will be evaluated as potential noninvasive therapies to support alveolar bone homeostasis and prevent periodontal bone loss.

Fusobacterium nucleatum Secretes Outer Membrane Vesicles and Promotes Intestinal Inflammation

Multiple studies have implicated microbes in the development of inflammation, but the mechanisms remain unknown. Bacteria in the genus Fusobacterium have been identified in the intestinal mucosa of patients with digestive diseases; thus, we hypothesized that Fusobacterium nucleatum promotes intestinal inflammation. The addition of >50 kDa F. nucleatum conditioned media, which contain outer membrane vesicles (OMVs), to colonic epithelial cells stimulated secretion of the proinflammatory cytokines interleukin-8 (IL-8) and tumor necrosis factor (TNF). In addition, purified F. nucleatum OMVs, but not compounds <50 kDa, stimulated IL-8 and TNF production; which was decreased by pharmacological inhibition of Toll-like receptor 4 (TLR4). These effects were linked to downstream effectors p-ERK, p-CREB, and NF-κB. F. nucleatum >50-kDa compounds also stimulated TNF secretion, p-ERK, p-CREB, and NF-κB activation in human colonoid monolayers. In mice harboring a human microbiota, pretreatment with antibiotics and a single oral gavage of F. nucleatum resulted in inflammation. Compared to mice receiving vehicle control, mice treated with F. nucleatum showed disruption of the colonic architecture, with increased immune cell infiltration and depleted mucus layers. Analysis of mucosal gene expression revealed increased levels of proinflammatory cytokines (KC, TNF, IL-6, IFN-γ, and MCP-1) at day 3 and day 5 in F. nucleatum-treated mice compared to controls. These proinflammatory effects were absent in mice who received F. nucleatum without pretreatment with antibiotics, suggesting that an intact microbiome is protective against F. nucleatum-mediated immune responses. These data provide evidence that F. nucleatum promotes proinflammatory signaling cascades in the context of a depleted intestinal microbiome.IMPORTANCE Several studies have identified an increased abundance of Fusobacterium in the intestinal tracts of patients with colon cancer, liver cirrhosis, primary sclerosing cholangitis, gastroesophageal reflux disease, HIV infection, and alcoholism. However, the direct mechanism(s) of action of Fusobacterium on pathophysiological within the gastrointestinal tract is unclear. These studies have identified that F. nucleatum subsp. polymorphum releases outer membrane vesicles which activate TLR4 and NF-κB to stimulate proinflammatory signals in vitro Using mice harboring a human microbiome, we demonstrate that F. nucleatum can promote inflammation, an effect which required antibiotic-mediated alterations in the gut microbiome. Collectively, these results suggest a mechanism by which F. nucleatum may contribute to intestinal inflammation.

Microbial interactions and immunity response in oral Candida species

Oral candidiasis are among the most common noncommunicable diseases, related with serious local and systemic illnesses. Although these infections can occur in all kinds of patients, they are more recurrent in immunosuppressed ones such as patients with HIV, hepatitis, cancer or under long antimicrobial treatments. Candida albicans continues to be the most frequently identified Candida spp. in these disorders, but other non-C. albicans Candida are rising. Understanding the immune responses involved in oral Candida spp. infections is a key feature to a successful treatment and to the design of novel therapies. In this review, we performed a literature search in PubMed and WoS, in order to examine and analyze common oral Candida spp.-bacteria/Candida-Candida interactions and the host immunity response in oral candidiasis.

Association between Candida species and periodontal disease: A systematic review

Periodontal diseases result in the inflammation of the supporting structures of the teeth, thereby leading to attachment loss and bone loss. One of the main etiological factors responsible for this condition is the presence of subgingival biofilms, comprising microorganisms, namely bacteria, viruses, and fungi. Candida species is one of the fungi reported to be found in periodontal disease which is suggestive of the presence of an association between these variables. The aim of this systematic review was to evaluate the association of Candida species with periodontal disease and determine the prevalence of these species in the patients affected with this disease. The articles related to the subject of interest were searched in several databases, including the PubMed, Web of Science, Google Scholar Medline, Embase, Cochrane Library, and Scopus. The search process was accomplished using three keywords, namely ‘‘Candida species’’, ‘‘Chronic periodontitis’’, and ‘‘Gingivitis’’. All the identified studies were comprehensively evaluated for the association of Candida species with periodontal disease. This systematic review included 23 articles, which assessed the prevalence of Candida species in periodontal diseases. The results of 21 studies were indicative of a positive association between Candida species and periodontal diseases. Accordingly, it was concluded that there is a strong association between the presence of Candida species and periodontal diseases

Pathogenetic Impact of Bacterial-Fungal Interactions

Polymicrobial infections are of paramount importance because of the potential severity of clinical manifestations, often associated with increased resistance to antimicrobial treatment. The intricate interplay with the host and the immune system, and the impact on microbiome imbalance, are of importance in this context. The equilibrium of microbiota in the human host is critical for preventing potential dysbiosis and the ensuing development of disease. Bacteria and fungi can communicate via signaling molecules, and produce metabolites and toxins capable of modulating the immune response or altering the efficacy of treatment. Most of the bacterial–fungal interactions described to date focus on the human fungal pathogen Candida albicans and different bacteria. In this review, we discuss more than twenty different bacterial–fungal interactions involving several clinically important human pathogens. The interactions, which can be synergistic or antagonistic, both in vitro and in vivo, are addressed with a focus on the quorum-sensing molecules produced, the response of the immune system, and the impact on clinical outcome.

Prevalence of Candida albicans in primary endodontic infections associated with a higher frequency of apical periodontitis in type two diabetes mellitus patients

To identify the prevalence of C. albicans in primary endodontic infections of type two diabetes mellitus (T2DM) patients and compare their clinical and radiographical characteristics with a non-diabetic control group, establishing the possible relationship between primary endodontic infection, T2DM, and C. albicans, since diabetes mellitus (DM), influences the development, course, and response to the treatment of apical periodontitis, but the presence of Candida albicans (C. albicans) has not been considered before. A total of 120 patients were selected and divided into two groups: 60 T2DM diagnosed patients and 60 non-diabetic controls. A clinical examination and radiographic analysis were performed to establish a periapical index score (PAI). Root canal samples were taken. Deoxyribonucleic acid (DNA) was extracted, and specific primers were used to identify C. albicans by polymerase chain reaction (PCR). A twofold increase in the prevalence of C. albicans in T2DM patients was observed in contrast to control patients (p = 0.0251). Sixty-five percent of T2DM patients with positive C. albicans scored a ≥ 3 PAI, while only 27% of the patients without C. albicans had a ≥ 3 PAI score (p = 0.0065). Long-term DM patients presented C. albicans more frequently (p < 0.0001). In this study, long-term T2DM patients carried C. albicans in their root canals more frequently when having a primary endodontic infection. Furthermore, this C. albicans presence seems to be related to a higher frequency of apical periodontitis.

Candida Interactions with the Oral Bacterial Microbiota

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

Microbial Ecology along the Gastrointestinal Tract

The ecosystem of the human gastrointestinal (GI) tract traverses a number of environmental, chemical, and physical conditions because it runs from the oral cavity to the anus. These differences in conditions along with food or other ingested substrates affect the composition and density of the microbiota as well as their functional roles by selecting those that are the most suitable for that environment. Previous studies have mostly focused on Bacteria, with the number of studies conducted on Archaea, Eukarya, and Viruses being limited despite their important roles in this ecosystem. Furthermore, due to the challenges associated with collecting samples directly from the inside of humans, many studies are still exploratory, with a primary focus on the composition of microbiomes. Thus, mechanistic studies to investigate functions are conducted using animal models. However, differences in physiology and microbiomes need to be clarified in order to aid in the translation of animal model findings into the context of humans. This review will highlight Bacteria, Archaea, Fungi, and Viruses, discuss differences along the GI tract of healthy humans, and perform comparisons with three common animal models: rats, mice, and pigs.

Assessment of Methylobacterium oryzae CBMB20 aggregates for salt tolerance and plant growth promoting characteristics for bio-inoculant development

Salinity is one of the major factors contributing to the loss of crop productivity and thereby impacting livelihood of people in more than 100 countries of the world and the area of land affected by salinity is increasing day by day. This will worsen due to various factors such as drought that might result in high soil salinity. Use of plant growth promoting rhizobacteria is one of the promising eco-friendly strategies for salinity stress management as part of sustainable agricultural practices. However, it requires selecting rhizobacteria with good survivability and adaptation to salt stress. In this study we report aggregation of Methylobacterium oryzae CBMB20 cells grown in media containing high C/N ratio (30:1) than in media containing low C/N ratio (7:1). Aggregated Methylobacterium oryzae CBMB20 cells exhibited enhanced tolerance to UV irradiation, heat, desiccation, different temperature regimes, oxidative stress, starvation and supported higher population in media. Poly-β-hydroxybutyrate accumulation, exopolysaccharide production, proline accumulation and biofilm formation were good at 100 mM salt concentration with good microbial cell hydrophobicity at both 50 and 100 mM than other concentrations. Both the aggregated and non-aggregated cells grown under 0-200 mM salt concentrations produced IAA even at 200 mM salt concentration with a peak at 100 mM concentration with aggregated cells producing significantly higher quantities. ACC deaminase activity was observed in all NaCl concentrations studied with gradual and drastic reduction in aggregated and non-aggregated cells over increased salt concentrations.

Pathogenic factors in Candida biofilm-related infectious diseases

Candida albicans is a commonly found member of the human microflora and is a major human opportunistic fungal pathogen. A perturbation of the microbiome can lead to infectious diseases caused by various micro-organisms, including C. albicans. Moreover, the interactions between C. albicans and bacteria are considered to play critical roles in human health. The major biological feature of C. albicans, which impacts human health, resides in its ability to form biofilms. In particular, the extracellular matrix (ECM) of Candida biofilm plays a multifaceted role and therefore may be considered as a highly attractive target to combat biofilm-related infectious diseases. In addition, extracellular DNA (eDNA) also plays a crucial role in Candida biofilm formation and its structural integrity and induces the morphological transition from yeast to the hyphal growth form during C. albicans biofilm development. This review focuses on pathogenic factors such as eDNA in Candida biofilm formation and its ECM production and provides meaningful information for future studies to develop a novel strategy to battle infectious diseases elicited by Candida-formed biofilm.

Morphological and physiological changes induced by contact-dependent interaction between Candida albicans and Fusobacterium nucleatum

Candida albicans and Fusobacterium nucleatum are well-studied oral commensal microbes with pathogenic potential that are involved in various oral polymicrobial infectious diseases. Recently, we demonstrated that F. nucleatum ATCC 23726 coaggregates with C. albicans SN152, a process mainly mediated by fusobacterial membrane protein RadD and Candida cell wall protein Flo9. The aim of this study was to investigate the potential biological impact of this inter-kingdom interaction. We found that F. nucleatum ATCC 23726 inhibits growth and hyphal morphogenesis of C. albicans SN152 in a contact-dependent manner. Further analysis revealed that the inhibition of Candida hyphal morphogenesis is mediated via RadD and Flo9 protein pair. Using a murine macrophage cell line, we showed that the F. nucleatum-induced inhibition of Candida hyphal morphogenesis promotes C. albicans survival and negatively impacts the macrophage-killing capability of C. albicans. Furthermore, the yeast form of C. albicans repressed F. nucleatum-induced MCP-1 and TNFα production in macrophages. Our study suggests that the interaction between C. albicans and F. nucleatum leads to a mutual attenuation of virulence, which may function to promote a long-term commensal lifestyle within the oral cavity. This finding has significant implications for our understanding of inter-kingdom interaction and may impact clinical treatment strategies.

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.

Alterations of Bacteroides sp., Neisseria sp., Actinomyces sp., and Streptococcus sp. populations in the oropharyngeal microbiome are associated with liver cirrhosis and pneumonia

BACKGROUND

The microbiomes of humans are associated with liver and lung inflammation. We identified and verified alterations of the oropharyngeal microbiome and assessed their association with cirrhosis and pneumonia.

METHODS

Study components were as follows: (1) determination of the temporal stability of the oropharyngeal microbiome; (2) identification of oropharyngeal microbial variation in 90 subjects; (3) quantitative identification of disease-associated bacteria. DNAs enriched in bacterial sequences were produced from low-biomass oropharyngeal swabs using whole genome amplification and were analyzed using denaturing gradient gel electrophoresis analysis.

RESULTS

Whole genome amplification combined with denaturing gradient gel electrophoresis analysis monitored successfully oropharyngeal microbial variations and showed that the composition of each subject's oropharyngeal microbiome remained relatively stable during the follow-up. The microbial composition of cirrhotic patients with pneumonia differed from those of others and clustered together in subgroup analysis. Further, species richness and the value of Shannon's diversity and evenness index increased significantly in patients with cirrhosis and pneumonia versus others (p < 0.001, versus healthy controls; p < 0.01, versus cirrhotic patients without pneumonia). Moreover, we identified variants of Bacteroides, Eubacterium, Lachnospiraceae, Neisseria, Actinomyces, and Streptococcus through phylogenetic analysis. Quantitative polymerase chain reaction assays revealed that the populations of Bacteroides, Neisseria, and Actinomycetes increased, while that of Streptococcus decreased in cirrhotic patients with pneumonia versus others (p < 0.001, versus Healthy controls; p < 0.01, versus cirrhotic patients without pneumonia).

CONCLUSIONS

Alterations of Bacteroides, Neisseria, Actinomyces, and Streptococcus populations in the oropharyngeal microbiome were associated with liver cirrhosis and pneumonia.

Fap2 of Fusobacterium nucleatum is a galactose-inhibitable adhesin involved in coaggregation, cell adhesion, and preterm birth

Fusobacterium nucleatum is a common oral anaerobe involved in periodontitis that is known to translocate and cause intrauterine infections. In the oral environment, F. nucleatum adheres to a large diversity of species, facilitating their colonization and creating biological bridges that stabilize the multispecies dental biofilm. Many of these interactions (called coadherences or coaggregations) are galactose sensitive. Galactose-sensitive interactions are also involved in the binding of F. nucleatum to host cells. Hemagglutination of some F. nucleatum strains is also galactose sensitive, suggesting that a single galactose-sensitive adhesin might mediate the interaction of fusobacteria with many partners and targets. In order to identify the fusobacterial galactose-sensitive adhesin, a system for transposon mutagenesis in fusobacteria was created. The mutant library was screened for hemagglutination deficiency, and three clones were isolated. All three clones were found to harbor the transposon in the gene coding for the Fap2 outer membrane autotransporter. The three fap2 mutants failed to show galactose-inhibitable coaggregation with Porphyromonas gingivalis and were defective in cell binding. A fap2 mutant also showed a 2-log reduction in murine placental colonization compared to that of the wild type. Our results suggest that Fap2 is a galactose-sensitive hemagglutinin and adhesin that is likely to play a role in the virulence of fusobacteria.

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.

Influence of fixed orthodontic appliances on the change in oral Candida strains among adolescents

Background/purpose

The aim of this study was to explore the presence and variability of oral Candida in adolescents before and during treatment with fixed orthodontic appliances.

Materials and methods

A total of 50 patients aged 10–18 years old were randomly selected for this study. Microorganism samples were obtained prior to and after orthodontic treatment and identified by culture methods. Molecular biology techniques were used to investigate the samples further and the effect of the orthodontic appliance on oral pathogenic yeasts was studied longitudinally.

Results

The percentage of patients with candidiasis and the total number of colony-forming units significantly increased 2 months after orthodontic treatment. Changes in the type of oral candidiasis prior to and after treatment were significant.

Conclusion

Fixed orthodontic appliances can influence the growth of oral pathogenic yeasts among adolescents.

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.

The human mycobiome in health and disease

The mycobiome, referring primarily to the fungal biota in an environment, is an important component of the human microbiome. Despite its importance, it has remained understudied. New culture-independent approaches to determine microbial diversity, such as next-generation sequencing methods, are greatly broadening our view of fungal importance. An integrative analysis of current studies shows that different body sites harbor specific fungal populations, and that diverse mycobiome patterns are associated with various diseases. By interfacing with other biomes, as well as with the host, the mycobiome probably contributes to the progression of fungus-associated diseases and plays an important role in health and disease.

The human mycobiome in health and disease

The mycobiome, referring primarily to the fungal biota in an environment, is an important component of the human microbiome. Despite its importance, it has remained understudied. New culture-independent approaches to determine microbial diversity, such as next-generation sequencing methods, are greatly broadening our view of fungal importance. An integrative analysis of current studies shows that different body sites harbor specific fungal populations, and that diverse mycobiome patterns are associated with various diseases. By interfacing with other biomes, as well as with the host, the mycobiome probably contributes to the progression of fungus-associated diseases and plays an important role in health and disease.

[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.

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.

Probiotics in periodontal health and disease

Macfarlane Burnett stated in 1962 that “By the late twentieth century, we can anticipate the virtual elimination of infectious diseases as a significant factor in social life”. Probiotics have become of interest to researchers in recent times. Time has come to shift the paradigm of treatment from specific bacteria elimination to altering bacterial ecology by probiotics. The development of resistance to a range of antibiotics by some important pathogens has raised the possibility of a return to the pre-antibiotic dark ages. Here, probiotics provide an effective alternative way, which is economical and natural to combat periodontal disease. Thus, a mere change in diet by including probiotic foods may halt, retard, or even significantly delay the pathogenesis of periodontal diseases, promoting a healthy lifestyle to fight periodontal infections.

Detection and identification of non-Candida albicans species in human oral lichen planus

Candida species were detected and identified in samples from the buccal mucosa, dorsal surface of the tongue and supragingival plaque of subjects with oral lichen planus (OLP). The Candida in the samples were cultured on selection agars, and identified by sequence analyses of 18S, 5.8S and 25/28S rRNA. The isolation frequency of Candida was higher in subjects with OLP than in those with healthy oral mucosa. Non-C. albicans were only isolated from people with OLP. These results support the notion that subjects with OLP are more likely to have oral colonization with Candida, and that non-C. albicans are specifically present in subjects with this condition.

Autoaggregation response of Fusobacterium nucleatum

Fusobacterium nucleatum is a gram-negative oral bacterial species associated with periodontal disease progression. This species is perhaps best known for its ability to adhere to a vast array of other bacteria and eukaryotic cells. Numerous studies of F. nucleatum have examined various coaggregation partners and inhibitors, but it is largely unknown whether these interactions induce a particular genetic response. We tested coaggregation between F. nucleatum ATCC strain 25586 and various species of Streptococcus in the presence of a semidefined growth medium containing saliva. We found that this condition could support efficient coaggregation but, surprisingly, also stimulated a similar degree of autoaggregation. We further characterized the autoaggregation response, since few reports have examined this in F. nucleatum. After screening several common coaggregation inhibitors, we identified l-lysine as a competitive inhibitor of autoaggregation. We performed a microarray analysis of the planktonic versus autoaggregated cells and found nearly 100 genes that were affected after only about 60 min of aggregation. We tested a subset of these genes via real-time reverse transcription-PCR and confirmed the validity of the microarray results. Some of these genes were also found to be inducible in cell pellets created by centrifugation. Based upon these data, it appears that autoaggregation activates a genetic program that may be utilized for growth in a high cell density environment, such as the oral biofilm.

Cross-kingdom interactions: Candida albicans and bacteria

Bacteria and fungi are found together in a myriad of environments and particularly in a biofilm, where adherent species interact through diverse signaling mechanisms. Yet, despite billions of years of coexistence, the area of research exploring fungal-bacterial interactions, particularly within the context of polymicrobial infections, is still in its infancy. However, reports describing a multitude of wide-ranging interactions between the fungal pathogen Candida albicans and various bacterial pathogens are on the rise. An example of a mutually beneficial interaction is coaggregation, a phenomenon that takes place in oral biofilms where the adhesion of C. albicans to oral bacteria is considered crucial for its colonization of the oral cavity. In contrast, the interaction between C. albicans and Pseudomonas aeruginosa is described as being competitive and antagonistic in nature. Another intriguing interaction is that occurring between Staphylococcus aureus and C. albicans, which although not yet fully characterized, appears to be initially synergistic. These complex interactions between such diverse and important pathogens would have significant clinical implications if they occurred in an immunocompromised host. Therefore, understanding the mechanisms of adhesion and signaling involved in fungal-bacterial interactions may lead to the development of novel therapeutic strategies for impeding microbial colonization and development of polymicrobial disease.

Laboratory maintenance of fusobacteria

This unit describes routine laboratory handling of fusobacteria. Different media that can be used to grow or enrich Fusobacterium nucleatum and other species of this genus are described. The growth and stock conditions as well as the susceptibility of F. nucleatum to oxygen in a pure culture are also discussed.

Candida albicans Als proteins mediate aggregation with bacteria and yeasts

Candida albicans occupies a microniche on mucosal surfaces where diverse microbial populations interact within a biofilm. Because C. albicans is intimately involved with other microbes in this environment we studied the interactions of C. albicans with other fungi and bacteria that form mixed microbial aggregates. Once aggregation is initiated, aggregates form rapidly and incorporate fungal as well as bacterial cells. The fungus formed mixed microbial aggregates with homotypic cells (i.e., self to self, e.g., C. albicans or Als1p-expressing yeast cells aggregating with cells bearing Als1p); with heterotypic cells (i.e., self to non-self, e.g., C. albicans or Alsp-expressing yeast cells aggregating with other Candida species); and with xenotypic cells (e.g., C. albicans or Alsp-expressing yeast cells forming aggregates with bacteria). When either of the C. albicans adhesins Als1p or Als5p was displayed on the surface of non-adherent Saccharomyces cerevisiae cells, the S. cerevisiae also mediated these mixed microbial interactions. Thus the Als adhesins are potentially important for the co-adhesion of mixed microbial communities in biofilms and on mucus surfaces.

A simplified technique for evaluating the adherence of yeasts to human vaginal epithelial cells

Thousands of women all over the world annually suffer of vulvovaginal candidiasis (VVC), an infection caused by yeasts, which mainly affect the mucosa of the vulva and vagina. The adherence of the yeasts to the mucosae is an essential step for colonization and predisposes the start of the infectious process. In this study, a technique capable of evaluating the adhesion of yeasts to human vaginal epithelial cells (HVEC) was employed. Twenty-five vaginal yeast isolates (10 Candida albicans, nine C. glabrata, two C. parapsilosis, one C. tropicalis, two Saccharomyces cerevisiae, and one Trichosporon sp.) were evaluated. A suspension of each yeast was co-incubated with HVEC obtained from a healthy donor in the ovulatory phase. After 1 hr, smears were made, stained with crystal violet and Papanicolaou, and the number of yeasts that adhered to 600 HVEC was evaluated. The adhesion of C. albicans was significantly greater than that of the other species and occurred mainly in the intermediate HVEC, rather than the superficial. In addition, the proposed technique, easy to execute and of low cost showed to be reproducible and enables the determination of the adherence capacity of different isolates, whose adhesion was confirmed by scanning electron microscopy.

Effect of oral bacteria on growth and survival of Candida albicans biofilms

The purpose of this study was to evaluate the effect of eight aerobic and anaerobic oral commensal bacterial species on in vitro Candida albicans biofilm development. A single isolate of C. albicans 2560 g, and eight different species of oral bacteria comprising, Actinomyces israelii, Lactobacillus acidophilus, Prevotella nigrescens, Porphyromonas gingivalis, Pseudomonas aeruginosa, Escherichia coli, Streptococcus mutans, and Streptococcus intermedius were studied using an in vitro biofilm assay. Biofilm formation was quantified in terms of the ability of Candida to grow on polystyrene plastic surfaces co-cultured with the foregoing bacteria. A viable cell count was used to quantify the sessile yeast growth and scanning electron microscopy was employed to confirm and visualize biofilm formation. Co-culture with differing concentrations of bacteria had variable effects on Candida biofilm formation. Co-culture with the highest concentrations of each of the foregoing bacteria resulted in a consistent reduction in the yeast counts in the candidal biofilm (P<0.05), except for L. acidophilus, S. mutans, and, S. intermedius co-cultures. Further, on regression analysis a significant negative correlation between the co-culture concentration of either P. gingivalis or E. coli and viable yeast counts in the biofilm was noted (P<0.05) although this was not evident for the other bacterial species. Taken together, our data indicate that, quantitative and qualitative nature of the bacteria modulate C. albicans biofilm formation in mixed species environments such as the oral cavity.

Identification and characterization of a novel adhesin unique to oral fusobacteria

Fusobacterium nucleatum is a gram-negative anaerobe that is prevalent in periodontal disease and infections of different parts of the body. The organism has remarkable adherence properties, binding to partners ranging from eukaryotic and prokaryotic cells to extracellular macromolecules. Understanding its adherence is important for understanding the pathogenesis of F. nucleatum. In this study, a novel adhesin, FadA (Fusobacterium adhesin A), was demonstrated to bind to the surface proteins of the oral mucosal KB cells. FadA is composed of 129 amino acid (aa) residues, including an 18-aa signal peptide, with calculated molecular masses of 13.6 kDa for the intact form and 12.6 kDa for the secreted form. It is highly conserved among F. nucleatum, Fusobacterium periodonticum, and Fusobacterium simiae, the three most closely related oral species, but is absent in the nonoral species, including Fusobacterium gonidiaformans, Fusobacterium mortiferum, Fusobacterium naviforme, Fusobacterium russii, and Fusobacterium ulcerans. In addition to FadA, F. nucleatum ATCC 25586 and ATCC 49256 also encode two paralogues, FN1529 and FNV2159, each sharing 31% identity with FadA. A double-crossover fadA deletion mutant, F. nucleatum 12230-US1, was constructed by utilizing a novel sonoporation procedure. The mutant had a slightly slower growth rate, yet its binding to KB and Chinese hamster ovarian cells was reduced by 70 to 80% compared to that of the wild type, indicating that FadA plays an important role in fusobacterial colonization in the host. Furthermore, due to its uniqueness to oral Fusobacterium species, fadA may be used as a marker to detect orally related fusobacteria. F. nucleatum isolated from other parts of the body may originate from the oral cavity.

New assay for measuring cell surface hydrophobicities of Candida dubliniensis and Candida albicans

Hydrophobic interactions, based on cell surface hydrophobicity (CSH), are among the many and varied mechanisms of adherence deployed by the pathogenic yeast Candida albicans. Recently it was shown that, unlike C. albicans, C. dubliniensis is a species that exhibits an outer fibrillar layer consistent with constant CSH. Previously, C. dubliniensis grown at 25 or 37 degrees C was shown to coaggregate with the oral anaerobic bacterium Fusobacterium nucleatum. C. albicans, however, demonstrated similar coaggregation only when hydrophobic or grown at 25 degrees C. This observation implied that coaggregation of Candida cells with F. nucleatum is associated with a hydrophobic yeast cell surface. To test this hypothesis, 42 C. albicans and 40 C. dubliniensis clinical isolates, including a C. albicans hydrophobic variant, were grown at 25 and 37 degrees C and tested with the established hydrophobicity microsphere assay, which determines CSH levels based on the number of microspheres attached to the yeast cells. The coaggregation assay was performed in parallel experiments. All C. dubliniensis isolates grown at either temperature, hydrophobic 25 degrees C-grown C. albicans isolates, and the C. albicans hydrophobic variant, unlike the 37 degrees C-hydrophilic C. albicans isolates, exhibited hydrophobic CSH levels with the microsphere assay and simultaneously showed maximum, 4+, coaggregation with F. nucleatum. The parallel results obtained for C. dubliniensis using both assays support the use of the CoAg assay both as a rapid assay to determine CSH and to differentiate between C. dubliniensis and C. albicans.

Coaggregation of Candida dubliniensis with Fusobacterium nucleatum

The binding of microorganisms to each other and oral surfaces contributes to the progression of microbial infections in the oral cavity. Candida dubliniensis, a newly characterized species, has been identified in human immunodeficiency virus-seropositive patients and other immunocompromised individuals. C. dubliniensis phenotypically resembles Candida albicans in many respects yet can be identified and differentiated as a unique Candida species by phenotypic and genetic profiles. The purpose of this study was to determine oral coaggregation (CoAg) partners of C. dubliniensis and to compare these findings with CoAg of C. albicans under the same environmental conditions. Fifteen isolates of C. dubliniensis and 40 isolates of C. albicans were tested for their ability to coaggregate with strains of Fusobacterium nucleatum, Peptostreptococcus micros, Peptostreptococcus magnus, Peptostreptococcus anaerobius, Porphyromonas gingivalis, and Prevotella intermedia. When C. dubliniensis and C. albicans strains were grown at 37 degrees C on Sabouraud dextrose agar, only C. dubliniensis strains coaggregated with F. nucleatum ATCC 49256 and no C. albicans strains showed CoAg. However, when the C. dubliniensis and C. albicans strains were grown at 25 or 45 degrees C, both C. dubliniensis and C. albicans strains demonstrated CoAg with F. nucleatum. Heating the C. albicans strains (grown at 37 degrees C) at 85 degrees C for 30 min or treating them with dithiothreitol allowed the C. albicans strains grown at 37 degrees C to coaggregate with F. nucleatum. CoAg at all growth temperatures was inhibited by mannose and alpha-methyl mannoside but not by EDTA or arginine. The CoAg reaction between F. nucleatum and the Candida species involved a heat-labile component on F. nucleatum and a mannan-containing heat-stable receptor on the Candida species. The CoAg reactions between F. nucleatum and the Candida species may be important in the colonization of the yeast in the oral cavity, and the CoAg of C. dubliniensis by F. nucleatum when grown at 37 degrees C provides a rapid, specific, and inexpensive means to differentiate C. dubliniensis from C. albicans isolates in the clinical laboratory.