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Streptococcus mutans and Candida albicans are frequently detected together in the plaque from patients with early childhood caries (ECC) and synergistically interact to form a cariogenic cross-kingdom biofilm. However, this biofilm is difficult to control. Thus, to achieve maximal efficacy within the complex biofilm microenvironment, nanoparticle carriers have shown increased interest in treating oral biofilms in recent years. Here, we assessed the anti-biofilm efficacy of farnesol (Far), a hydrophobic antibacterial drug and repressor of Candida filamentous forms, against cross-kingdom biofilms employing drug delivery via polymeric nanoparticle carriers (NPCs). We also evaluated the effect of the strategy on teeth enamel demineralization. The farnesol-loaded NPCs (NPC+Far) resulted in a 2-log CFU/mL reduction of S. mutans and C. albicans (hydroxyapatite disc biofilm model). High-resolution confocal images further confirmed a significant reduction in exopolysaccharides, smaller microcolonies of S. mutans, and no hyphal form of C. albicans after treatment with NPC+Far on human tooth enamel (HT) slabs, altering the biofilm 3D structure. Furthermore, NPC+Far treatment was highly effective in preventing enamel demineralization on HT, reducing lesion depth (79% reduction) and mineral loss (85% reduction) versus vehicle PBS-treated HT, while NPC or Far alone had no differences with the PBS. The drug delivery via polymeric NPCs has the potential for targeting bacterial-fungal biofilms associated with a prevalent and costly pediatric oral disease, such as ECC.

Fungi and bacteria often engage in complex interactions, such as the formation of multicellular biofilms within the human body. Knowledge about how interkingdom biofilms initiate and coalesce into higher-level communities and which functions the different species carry out during biofilm formation remain limited. We found native-state assemblages of Candida albicans (fungi) and Streptococcus mutans (bacteria) with highly structured arrangement in saliva from diseased patients with childhood tooth decay. Further analyses revealed that bacterial clusters are attached within a network of fungal yeasts, hyphae, and exopolysaccharides, which bind to surfaces as a preassembled cell group. The interkingdom assemblages exhibit emergent functions, including enhanced surface colonization and growth rate, stronger tolerance to antimicrobials, and improved shear resistance, compared to either species alone. Notably, we discovered that the interkingdom assemblages display a unique form of migratory spatial mobility that enables fast spreading of biofilms across surfaces and causes enhanced, more extensive tooth decay. Using mutants, selective inactivation of species, and selective matrix removal, we demonstrate that the enhanced stress resistance and surface mobility arise from the exopolymeric matrix and require the presence of both species in the assemblage. The mobility is directed by fungal filamentation as hyphae extend and contact the surface, lifting the assemblage with a “forward-leaping motion.” Bacterial cell clusters can “hitchhike” on this mobile unit while continuously growing, to spread across the surface three-dimensionally and merge with other assemblages, promoting community expansion. Together, our results reveal an interkingdom assemblage in human saliva that behaves like a supraorganism, with disease-causing emergent functionalities that cannot be achieved without coassembly.

The oral cavity, as the entry point to the body, may play a critical role in the pathogenesis of SARS-CoV-2 infection that has caused a global outbreak of the coronavirus disease 2019 (COVID-19). Available data indicate that the oral cavity may be an active site of infection and an important reservoir of SARS-CoV-2. Considering that the oral surfaces are colonized by a diverse microbial community, it is likely that viruses have interactions with the host microbiota. Patients infected by SARS-CoV-2 may have alterations in the oral and gut microbiota, while oral species have been found in the lung of COVID-19 patients. Furthermore, interactions between the oral, lung, and gut microbiomes appear to occur dynamically whereby a dysbiotic oral microbial community could influence respiratory and gastrointestinal diseases. However, it is unclear whether SARS-CoV-2 infection can alter the local homeostasis of the resident microbiota, actively cause dysbiosis, or influence cross-body sites interactions. Here, we provide a conceptual framework on the potential impact of SARS-CoV-2 oral infection on the local and distant microbiomes across the respiratory and gastrointestinal tracts (‘oral-tract axes’), which remains largely unexplored. Studies in this area could further elucidate the pathogenic mechanism of SARS-CoV-2 and the course of infection as well as the clinical symptoms of COVID-19 across different sites in the human host.

Background The relationship between oral microbiota and IE (infective endocarditis) is well established. Opportunistic pathogens in normal oral flora enter the bloodstream through daily oral cleaning or invasive dental procedures, leading to the occurrence of infective endocarditis. An in vitro iron-deficient condition leads to a drastic community shift in oral microbiota with increasing proportions of taxa related to infective endocarditis. To investigate the relationship among insufficient iron supply, oral microbiota and the risk of IE and to conduct a population amplification study, iron-deficiency anaemia is used as an in vivo model. Methods This cross-sectional study enrolled 24 primary iron-deficiency anemia (IDA) patients from 2015.6 to 2016.6 from the hematology department of West China Hospital, Sichuan University, and 24 healthy controls. High-throughput sequencing compared the dental plaque microbiota of 24 IDA (iron-deficiency anaemia) patients and 24 healthy controls. Results Sequences were classified into 12 phyla, 28 classes, 50 orders, 161 genera and 497 OTUs (the IDA and control groups shared the same 384 OTUs). Iron deficiency leads to lower internal diversity in the oral flora. The abundances of genera Corynebacterium, Neisseria, Cardiobacterium, Capnocytophaga, and Aggregatibacter were significantly higher in healthy controls, while genera Lactococcus, Enterococcus, Lactobacillus, Pseudomonas and Moraxella showed higher proportions in the IDA group (P P Conclusions Without an increase of oral streptococci, the main pathogen of IE, it is difficult to determine whether IDA can increase the risk of IE. However, the iron-deficient condition did lead to changes in the oral microbiota community structure. The genera that showed higher proportions in the IDA group were frequently reported as antibiotic-resistant. As antibiotics are commonly recommended to prevent IE before dental procedures, this study offers new ideas of personalized prevention of IE.

Objective Dentin remineralization at the bonded interface would protect it from external risk factors, therefore, would enhance the longevity of restoration and combat secondary caries. Dental biofilm, as one of the critical biological factors in caries formation, should not be neglected in the assessment of caries preventive agents. In this work, the remineralization effectiveness of demineralized human dentin in a multi-species dental biofilm environment via an adhesive containing nanoparticles of amorphous calcium phosphate (NACP) and dimethylaminohexadecyl methacrylate (DMAHDM) was investigated. Methods Dentin demineralization was promoted by subjecting samples to a three-species acidic biofilm containing Streptococcus mutans, Streptococcus sanguinis, Streptococcus gordonii for 24 h. Samples were divided into a control group, a DMAHDM adhesive group, an NACP group, and an NACP + DMAHDM adhesive group. A bonded model containing a control-bonded group, a DMAHDM-bonded group, an NACP-bonded group, and an NACP + DMAHDM-bonded group was also included in this study. All samples were subjected to a remineralization protocol consisting of 4-h exposure per 24-h period in brain heart infusion broth plus 1% sucrose (BHIS) followed by immersion in artificial saliva for the remaining period. The pH of BHIS after 4-h immersion was measured every other day. After 14 days, the biofilm was assessed for colony-forming unit (CFU) count, lactic acid production, live/dead staining, and calcium and phosphate content. The mineral changes in the demineralized dentin samples were analyzed by transverse microradiography. Results The in vitro experiment results showed that the NACP + DMAHDM adhesive effectively achieved acid neutralization, decreased biofilm colony-forming unit (CFU) count, decreased biofilm lactic acid production, and increased biofilm calcium and phosphate content. The NACP + DMAHDM adhesive group had higher remineralization value than the NACP or DMAHDM alone adhesive group. Significance The NACP + DMAHDM adhesive was effective in remineralizing dentin lesion in a biofilm model. It is promising to use NACP + DMAHDM adhesive to protect bonded interface, inhibit secondary caries, and prolong the longevity of restoration.

Streptococcus is a genus of oval-shaped bacteria that act as both commensals and pathogens. Streptococcal infections are relevant to high morbidity and huge socioeconomic costs, with drug resistant strains becoming an increasing threat. Cell division plays an essential role during streptococcal colonization and infection, rendering it an ideal target for antibiotics. Substantial progress has been made to uncover the molecular biology and cellular processes of cell division, favoring the target strategies. This review discusses recent advances in our understanding of streptococcal cell division and its regulatory mechanisms regarding the conserved proteins, by comparing with model rods. Peptidoglycan synthesis that involved in septum formation and the maintenance of the unique oval shape have been spatiotemporally controlled in concert with the pace of division. With newly available tools of genetic and cytological study, streptococci will become an additional model bacterial system for cytokinesis and novel therapeutic agents that target cell division.

Bacterial cell division is initiated by tubulin homologue FtsZ that assembles into a ring structure at mid-cell to facilitate cytokinesis. EzrA has been identified to be implicated in FtsZ-ring dynamics and cell wall biosynthesis during cell division of Bacillus subtilis and Staphylococcus aureus, the model rod and cocci. However, its role in pathogenic streptococci remains largely unknown. Here, the role of EzrA was investigated in Streptococcus mutans, the primary etiological agent of human dental caries, by constructing an ezrA in-frame deletion mutant. Our data showed that the ezrA mutant was slow-growing with a shortened length and extended width round cell shape compared to the wild type, indicating a delay in cell division with abnormalities of peptidoglycan biosynthesis. Additionally, FtsZ irregularly localized in dividing ezrA mutant cells forming angled division planes, potentially contributing to an aberrant cell shape. Furthermore, investigation using single-species cariogenic biofilm model revealed that deletion of ezrA resulted in defective biofilm formation with less extracellular polysaccharides and altered three-dimensional biofilm architecture. Unexpectedly, in a dual-species ecological model, the ezrA mutant exhibited substantially lower tolerance for H2 O2 and reduced competitiveness against one commensal species, Streptococcus sanguinis. Taken together, these results demonstrate that EzrA plays a key role in regulating cell division and maintaining a normal morphology in S. mutans and is required for its robust biofilm formation/interspecies competition. Therefore, EzrA protein represents a potential therapeutic target in the development of drugs controlling dental caries and other biofilm-related diseases.

GntR family transcription factors have been implicated in the regulation of carbohydrate transport and metabolism in many bacteria. However, the function of this transcription factor family is poorly studied in Streptococcus mutans, which is a commensal bacterium in the human oral cavity and a well-known cariogenic pathogen. One of the most important virulence traits of S. mutans is its ability to transport and metabolize carbohydrates. In this study, we identified a GntR transcription factor in S. mutans named StsR (Sugar Transporter Systems Regulator). The deletion of the stsR gene in S. mutans caused a decrease in both the formation of biofilm and the production of extracellular polysaccharides (EPS) at early stage. Global gene expression profiling revealed that the expression levels of 188 genes were changed in the stsR mutant, which could be clustered with the sugar PTS and ABC transporters. Furthermore, StsR protein was purified and its conserved DNA binding motif was determined using electrophoretic mobility shift assays (EMSA) and DNase I footprinting assays. Collectively, the results of this research indicate that StsR is an important transcription factor in S. mutans that regulates the expression of sugar transporter genes, production of EPS and formation of biofilm.