Competence-Stimulating-Peptide-Dependent Localized Cell Death and Extracellular DNA Production in Streptococcus mutans Biofilms

Analyses of the Antibiofilm Activity of o-Phenanthroline Monohydrate against Enterococcus faecalis and Staphylococcus aureus and the Mechanisms Underlying These Effects

Enterococcus faecalis and Staphylococcus aureus exhibit robust biofilm formation capabilities, the formation of which is closely linked to pathogenicity and drug resistance, thereby resulting in host infection and treatment failure. o-Phenanthroline monohydrate (o-Phen) and its derivatives demonstrate a wide range of antibacterial and antifungal activities. In this study, we aimed to explore the antibiofilm activity of o-Phen to E. faecalis and S. aureus and provide insights into the molecular mechanisms for combating biofilm resistance. We demonstrated that o-Phen possesses significant antibacterial and antibiofilm properties against E. faecalis and S. aureus, inducing alterations in bacterial morphology, compromising cell membrane integrity, and exhibiting synergistic effects with β-lactam antibiotics at sub-MIC concentrations. The adhesion ability and automatic condensation capacity of, and synthesis of, extracellular polymers by E. faecalis cells were reduced by o-Phen, resulting in the inhibition of biofilm formation. Importantly, transcriptome analysis revealed 354 upregulated and 456 downregulated genes in o-Phen-treated E. faecalis. Differentially expressed genes were enriched in 11 metabolism-related pathways, including amino acid metabolism, pyrimidine metabolism, and glycolysis/gluconeogenesis. Moreover, the oppA, CeuA, and ZnuB genes involved in the ABC transport system, and the PBP1A penicillin-binding protein-coding genes sarA and mrcA were significantly downregulated. The multidrug efflux pump system and membrane permeability genes mdtG and hlyD, and bacterial adhesion-related genes, including adcA and fss2 were also downregulated, while mraZ and ASP23 were upregulated. Thus, o-Phen is anticipated to be an effective alternative drug for the treatment of E. faecalis and S. aureus biofilm-associated infections.

[Study on biofilm formation and heterogeneity in Clostridium perfringens]

Many bacteria form biofilms and survive in the actual environment. Biofilms are not only a major form of bacteria but are also involved in tolerance to environmental stresses and antibiotics, suggesting the association with bacterial pathogenesis. Cells within biofilms display phenotypic heterogeneity; thus, even bacteria, unicellular organisms, can functionally differentiate and show multicellular behavior. Therefore, it is necessary to understand bacteria as a population to control their survival and pathogenesis in the actual environment. Previously, we found that Clostridium perfringens, an anaerobic pathogenic bacterium, form different structures in different temperatures and phenotypic heterogeneity on biofilm matrix gene expression within the biofilm. In this article, I summarize the results of our research on biofilms and their heterogeneity, the mechanisms of post-transcriptional gene expression regulation of virulence genes, and bacteria-host interactions mediated by extracellular membrane vesicles.

Identification of a Novel Gene Involved in Cell-to-cell Communication-induced Cell Death and eDNA Production in Streptococcus mutans

Streptococcus mutans is a major caries-causing bacterium that forms firmly attached biofilms on tooth surfaces. Biofilm formation by S. mutans consists of polysaccharide-dependent and polysaccharide-independent processes. Among polysaccharide-independent processes, extracellular DNA (eDNA) mediates the initial attachment of cells to surfaces. We previously reported that the secreted peptide signal, competence-stimulating peptide (CSP) induced cell death in a subpopulation of cells, leading to autolysis-mediated eDNA release. The autolysin gene lytF, the expression of which is stimulated by CSP, has been shown to mediate CSP-dependent cell death, while cell death was not entirely abolished in the lytF deletion mutant, indicating the involvement of other factors. To identify novel genes involved in CSP-dependent cell death, we herein compared transcriptomes between live and dead cells derived from an isogenic population. The results obtained revealed the accumulation of several mRNAs in dead cells. The deletion of SMU_1553c, a putative bacteriocin gene, resulted in significant reductions in CSP-induced cell death and eDNA production levels from those in the parental strain. Moreover, in the double mutant strain of lytF and SMU_1553c, cell death and eDNA production in response to synthetic CSP were completely abolished under both planktonic and biofilm conditions. These results indicate that SMU_1553c is a novel cell death-related factor that contributes to CSP-dependent cell death and eDNA production.

Short-chain fatty acids inhibit the biofilm formation of Streptococcus gordonii through negative regulation of competence-stimulating peptide signaling pathway

Streptococcus gordonii, a Gram-positive commensal bacterium, is an opportunistic pathogen closely related to initiation and progression of various oral diseases, such as periodontitis and dental caries. Its biofilm formation is linked with the development of such diseases by enhanced resistance against antimicrobial treatment or host immunity. In the present study, we investigated the effect of short-chain fatty acids (SCFAs) on the biofilm formation of S. gordonii. SCFAs, including sodium acetate (NaA), sodium propionate (NaP), and sodium butyrate (NaB), showed an effective inhibitory activity on the biofilm formation of S. gordonii without reduction in bacterial growth. SCFAs suppressed S. gordonii biofilm formation at early time points whereas SCFAs did not affect its preformed biofilm. A quorum-sensing system mediated by competence-stimulating peptide (CSP) is known to regulate biofilm formation of streptococci. Interestingly, SCFAs substantially decreased mRNA expression of comD and comE, which are CSP-sensor and its response regulator responsible for CSP pathway, respectively. Although S. gordonii biofilm formation was enhanced by exogenous synthetic CSP treatment, such effect was not observed in the presence of SCFAs. Collectively, these results suggest that SCFAs have an anti-biofilm activity on S. gordonii through inhibiting comD and comE expression which results in negative regulation of CSP quorum-sensing system. SCFAs could be an effective anti-biofilm agent against S. gordonii for the prevention of oral diseases.

Effects of lipid emulsions on the formation of Escherichia coli-Candida albicans mixed-species biofilms on PVC

Patients receiving lipid emulsions are at increased risk of contracting catheter-related bloodstream infections (CRBSIs) in the clinic. More than 15% of CRBSIs are polymicrobial. The objective of this study was to explore the effects of lipid emulsions on the formation of Escherichia coli (E. coli)–Candida albicans (C. albicans) mixed-species biofilms (BFs) on polyvinyl chloride (PVC) surfaces and the underlying mechanism. Mixed-species BFs were produced by coculturing E. coli and C. albicans with PVC in various concentrations of lipid emulsions. Crystal violet staining and XTT assays were performed to test the mixed-species BF biomass and the viability of microbes in the BFs. The microstructures of the BFs were observed by an approach that combined confocal laser scanning microscopy, fluorescence in situ hybridization, and scanning electron microscopy. The study found that lipid emulsions could promote the formation of E. coli–C. albicans mixed-species BFs, especially with 10% lipid emulsions. The mechanism by which lipid emulsions promote mixed-species BF formation may involve significant upregulation of the expression of the flhDC, iha, HTA1, and HWP1 genes, which are associated with bacterial motility, adhesion, and BF formation. The results derived from this study necessitate strict aseptic precautions when handling lipid emulsions and avoiding the use of high concentrations of lipid emulsions for as long as possible.

The oralome and its dysbiosis: New insights into oral microbiome-host interactions

The oralome is the summary of the dynamic interactions orchestrated between the ecological community of oral microorganisms (comprised of up to approximately 1000 species of bacteria, fungi, viruses, archaea and protozoa - the oral microbiome) that live in the oral cavity and the host. These microorganisms form a complex ecosystem that thrive in the dynamic oral environment in a symbiotic relationship with the human host. However, the microbial composition is significantly affected by interspecies and host-microbial interactions, which in turn, can impact the health and disease status of the host. In this review, we discuss the composition of the oralome and inter-species and host-microbial interactions that take place in the oral cavity and examine how these interactions change from healthy (eubiotic) to disease (dysbiotic) states. We further discuss the dysbiotic signatures associated with periodontitis and caries and their sequalae, (e.g., tooth/bone loss and pulpitis), and the systemic diseases associated with these oral diseases, such as infective endocarditis, atherosclerosis, diabetes, Alzheimer's disease and head and neck/oral cancer. We then discuss current computational techniques to assess dysbiotic oral microbiome changes. Lastly, we discuss current and novel techniques for modulation of the dysbiotic oral microbiome that may help in disease prevention and treatment, including standard hygiene methods, prebiotics, probiotics, use of nano-sized drug delivery systems (nano-DDS), extracellular polymeric matrix (EPM) disruption, and host response modulators.