Microbiota Association and Profiling of Gingival Sulci and Root Canals of Teeth with Primary or Secondary/Persistent Endodontic Infections.

INTRODUCTION: Microbiota associated with primary endodontic infection (PEI) and secondary/persistent endodontic infection (SPEI) must be characterized to elucidate pathogenesis in apical periodontitis and bacterial biomarkers identified for diagnostic and therapeutic applications. METHODS: This study analyzed the microbial community profiles of root canals and gingival sulci (sulcus-E) for teeth with PEI (n = 10) or SPEI (n = 10), using the Illumina MiSeq platform. Bacterial samples from gingival sulci (sulcus-C) of healthy contralateral teeth served as controls. RESULTS: There were 15 phyla, 177 genera, and 340 species identified. The number and diversity of bacteria in root canals did not differ significantly between PEI and SPEI. Proteobacteria, Firmicutes, Fusobacteria, Bacteroidetes, and Actinobacteria were the dominant phyla in both groups. At the genus level, Lancefieldella, Bifidobacterium, Stomatobaculum, and Schaalia were enriched in root canals with SPEI. Of significance, Lancefieldella was observed in both root canals and sulcus-E of teeth with SPEI. At the species level, Neisseria macacae, Streptococcus gordonii, Bifidobacterium dentium, Stomatobaculum longum, and Schaalia odontolytica were increased significantly in root canals with SPEI compared to PEI. Oribacterium species, Streptococcus salivarius, Lancefieldella parvula, Prevotella denticola, and Oribacterium asaccharolyticum were more abundant in sulcus-E of teeth with SPEI compared to PEI. CONCLUSIONS: There were distinctive and differing predominant bacterial species associated with the root canals and gingival sulci between teeth with PEI and SPEI. Specific bacteria identified in sulcus-E and root canals of teeth with SPEI could serve as noninvasive diagnostic biomarkers for detecting SPEI.

Bacillus subtilis Induces Human Beta Defensin-2 Through its Lipoproteins in Human Intestinal Epithelial Cells.

Human intestinal epithelial cells (IECs) play an important role in maintaining gut homeostasis by producing antimicrobial peptides (AMPs). Bacillus subtilis, a commensal bacterium, is considered a probiotic. Although its protective effects on intestinal health are widely reported, the key component of B. subtilis responsible for its beneficial effects remains elusive. In this study, we tried to identify the key molecules responsible for B. subtilis-induced AMPs and their molecular mechanisms in a human IEC line, Caco-2. B. subtilis increased human beta defensin (HBD)-2 mRNA expression in a dose- and time-dependent manner. Among the B. subtilis microbe-associated molecular patterns, lipoprotein (LPP) substantially increased the mRNA expression and protein production of HBD-2, whereas lipoteichoic acid and peptidoglycan did not show such effects. Those results were confirmed in primary human IECs. In addition, both LPP recognition and HBD-2 secretion mainly took place on the apical side of fully differentiated and polarized Caco-2 cells through Toll-like receptor 2-mediated JNK/p38 MAP kinase/AP-1 and NF-κB pathways. HBD-2 efficiently inhibited the growth of the intestinal pathogens Staphylococcus aureus and Bacillus cereus. Furthermore, LPPs pre-incubated with lipase or proteinase K decreased LPP-induced HBD-2 expression, suggesting that the lipid and protein moieties of LPP are crucial for HBD-2 expression. Q Exactive Plus mass spectrometry identified 35 B. subtilis LPP candidates within the LPP preparation, and most of them were ABC transporters. Taken together, these results suggest that B. subtilis promotes HBD-2 secretion in human IECs mainly with its LPPs, which might enhance the protection from intestinal pathogens.

Lipoteichoic acid inhibits osteoclast differentiation and bone resorption via interruption of gelsolin-actin dissociation.

Bone resorption can be caused by excessive differentiation and/or activation of bone-resorbing osteoclasts. While microbe-associated molecular patterns can influence the differentiation and activation of bone cells, little is known about the role of lipoteichoic acid (LTA), a major cell wall component of Gram-positive bacteria, in the regulation of bone metabolism. In this study, we investigated the effect of LTA on bone metabolism using wild-type Staphylococcus aureus and the LTA-deficient mutant strain. LTA-deficient S. aureus induced higher bone loss and osteoclast differentiation than wild-type S. aureus. LTA isolated from S. aureus (SaLTA) inhibited osteoclast differentiation from committed osteoclast precursors in the presence of various osteoclastogenic factors by downregulating the expression of NFATc1. Remarkably, SaLTA attenuated the osteoclast differentiation from committed osteoclast precursors of TLR2-/- or MyD88-/- mice and from the committed osteoclast precursors transfected with paired immunoglobulin-like receptor B-targeting siRNA. SaLTA directly interacted with gelsolin, interrupting the gelsolin-actin dissociation which is a critical process for osteoclastogenesis. Moreover, SaLTA suppressed the mRNA expression of dendritic cell-specific transmembrane protein, ATPase H+ transporting V0 subunit D2, and Integrin, which encode proteins involved in cell-cell fusion of osteoclasts. Notably, LTAs purified from probiotics, including Bacillus subtilis, Enterococcus faecalis, and Lactobacillus species, also suppressed Pam2CSK4- or RANKL-induced osteoclast differentiation. Taken together, these results suggest that LTAs have anti-resorptive activity through the inhibition of osteoclastogenesis by interfering with the gelsolin-actin dissociation and may be used as effective therapeutic agents for the prevention or treatment of inflammatory bone diseases.

Butyrate potentiates Enterococcus faecalis lipoteichoic acid-induced inflammasome activation via histone deacetylase inhibition.

Enterococcus faecalis, a Gram-positive opportunistic pathogen having lipoteichoic acid (LTA) as a major virulence factor, is closely associated with refractory apical periodontitis. Short-chain fatty acids (SCFAs) are found in the apical lesion and may affect inflammatory responses induced by E. faecalis. In the current study, we investigated inflammasome activation by E. faecalis LTA (Ef.LTA) and SCFAs in THP-1 cells. Among SCFAs, butyrate in combination with Ef.LTA markedly enhanced caspase-1 activation and IL-1ß secretion whereas these were not induced by Ef.LTA or butyrate alone. Notably, LTAs from Streptococcus gordonii, Staphylococcus aureus, and Bacillus subtilis also showed these effects. Activation of TLR2/GPCR, K+ efflux, and NF-κB were necessary for the IL-1ß secretion induced by Ef.LTA/butyrate. The inflammasome complex comprising NLRP3, ASC, and caspase-1 was activated by Ef.LTA/butyrate. In addition, caspase-4 inhibitor diminished IL-1ß cleavage and release, indicating that non-canonical activation of the inflammasome is also involved. Ef.LTA/butyrate induced Gasdermin D cleavage, but not the release of the pyroptosis marker, lactate dehydrogenase. This indicated that Ef.LTA/butyrate induces IL-1ß production without cell death. Trichostatin A, a histone deacetylase (HDAC) inhibitor, enhanced Ef.LTA/butyrate-induced IL-1ß production, indicating that HDAC is engaged in the inflammasome activation. Furthermore, Ef.LTA and butyrate synergistically induced the pulp necrosis that accompanies IL-1ß expression in the rat apical periodontitis model. Taken all these results together, Ef.LTA in the presence of butyrate is suggested to facilitate both canonical- and non-canonical inflammasome activation in macrophages via HDAC inhibition. This potentially contributes to dental inflammatory diseases such as apical periodontitis, particularly associated with Gram-positive bacterial infection.

Muramyl dipeptide alleviates estrogen deficiency-induced osteoporosis through canonical Wnt signaling.

Wnt signaling is a positive regulator of bone formation through the induction of osteoblast differentiation and down-regulation of osteoclast differentiation. We previously reported that muramyl dipeptide (MDP) increases bone volume by increasing osteoblast activity and attenuating osteoclast activity in receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoporotic model mice. In this study, we investigated whether MDP could alleviate post-menopausal osteoporosis through Wnt signaling regulation in an ovariectomy (OVX)-induced mouse osteoporosis model. MDP-administered OVX mice exhibited higher bone volume and bone mineral density than mice of the control group. MDP significantly increased P1NP in the serum of OVX mice, implying increased bone formation. The expression of pGSK3ß and ß-catenin in the distal femur of OVX mice was lower than that in the distal femur of sham-operated mice. Yet, the expression of pGSK3ß and ß-catenin was increased in MDP-administered OVX mice compared with OVX mice. In addition, MDP increased the expression and transcriptional activity of ß-catenin in osteoblasts. MDP inhibited the proteasomal degradation of ß-catenin via the down-regulation of its ubiquitination by GSK3ß inactivation. When osteoblasts were pretreated with Wnt signaling inhibitors, DKK1 or IWP-2, the induction of pAKT, pGSK3ß, and ß-catenin was not observed. In addition, nucleotide oligomerization domain-containing protein 2-deficient osteoblasts were not sensitive to MDP. MDP-administered OVX mice exhibited fewer tartrate-resistant acid phosphatase (TRAP)-positive cells than did OVX mice, attributed to a decrease in the RANKL/OPG ratio. In conclusion, MDP alleviates estrogen deficiency-induced osteoporosis through canonical Wnt signaling and could be an effective therapeutic for the treatment of post-menopausal bone loss. © 2023 The Pathological Society of Great Britain and Ireland.

RNA-Seq-based transcriptome analysis of methicillin-resistant Staphylococcus aureus growth inhibition by propionate.

Staphylococcus aureus is a pathogen that causes a variety of infectious diseases such as pneumonia, endocarditis, and septic shock. Methicillin-resistant S. aureus (MRSA) evades virtually all available treatments, creating the need for an alternative control strategy. Although we previously demonstrated the inhibitory effect of sodium propionate (NaP) on MRSA, the regulatory mechanism of this effect remains unclear. In this study, we investigated the regulatory mechanism responsible for the inhibitory effect of NaP on MRSA using RNA-Seq analysis. Total RNAs were isolated from non-treated and 50 mM NaP-treated S. aureus USA300 for 3 h and transcriptional profiling was conducted by RNA-Seq analysis. A total of 171 differentially expressed genes (DEGs) with log2 fold change ≥2 and p < 0.05 was identified in the NaP treatment group compared with the control group. Among the 171 genes, 131 were up-regulated and 40 were down-regulated. Upon gene ontology (GO) annotation analysis, total 26 specific GO terms in "Biological process," "Molecular function," and "Cellular component" were identified in MRSA treated with NaP for 3 h. "Purine metabolism"; "riboflavin metabolism"; and "glycine, serine, and threonine metabolism" were identified as major altered metabolic pathways among the eight significantly enriched KEGG pathways in MRSA treated with NaP. Furthermore, the MRSA strains deficient in purF, ilvA, ribE, or ribA, which were the up-regulated DEGs in the metabolic pathways, were more susceptible to NaP than wild-type MRSA. Collectively, these results demonstrate that NaP attenuates MRSA growth by altering its metabolic pathways, suggesting that NaP can be used as a potential bacteriostatic agent for prevention of MRSA infection.

Induction of Apoptotic Cell Death by Oral Streptococci in Human Periodontal Ligament Cells.

Initiation and progression of oral infectious diseases are associated with streptococcal species. Bacterial infection induces inflammatory responses together with reactive oxygen species (ROS), often causing cell death and tissue damage in the host. In the present study, we investigated the effects of oral streptococci on cytotoxicity and ROS production in human periodontal ligament (PDL) cells. Streptococcus gordonii showed cell cytotoxicity in a dose- and time-dependent manner. The cytotoxicity might be due to apoptosis since S. gordonii increased annexin V-positive cells, and the cytotoxicity was reduced by an apoptosis inhibitor, Z-VAD-FMK. Other oral streptococci such as Streptococcus mitis, Streptococcus sanguinis, and Streptococcus sobrinus also induced apoptosis, whereas Streptococcus mutans did not. All streptococci tested except S. mutans triggered ROS production in human PDL cells. Interestingly, however, streptococci-induced apoptosis appears to be ROS-independent, as the cell death induced by S. gordonii was not recovered by the ROS inhibitor, resveratrol or n-acetylcysteine. Instead, hydrogen peroxide (H2O2) appears to be important for the cytotoxic effects of streptococci since most oral streptococci except S. mutans generated H2O2, and the cytotoxicity was dramatically reduced by catalase. Furthermore, streptococcal lipoproteins are involved in cytotoxicity, as we observed that cytotoxicity induced by the lipoprotein-deficient S. gordonii mutant was less potent than that by the wild-type and was attenuated by anti-TLR2-neutralizing antibody. Indeed, lipoproteins purified from S. gordonii alone were sufficient to induce cytotoxicity. Notably, S. gordonii lipoproteins did not induce H2O2 or ROS but cooperatively induced cell death when co-treated with H2O2. Taken together, these results suggest that most oral streptococci except S. mutans efficiently induce damage to human PDL cells by inducing apoptotic cell death with bacterial H2O2 and lipoproteins, which might contribute to the progression of oral infectious diseases such as apical periodontitis.

Regulation of Bone Cell Differentiation and Activation by Microbe-Associated Molecular Patterns.

Gut microbiota has emerged as an important regulator of bone homeostasis. In particular, the modulation of innate immunity and bone homeostasis is mediated through the interaction between microbe-associated molecular patterns (MAMPs) and the host pattern recognition receptors including Toll-like receptors and nucleotide-binding oligomerization domains. Pathogenic bacteria such as Porphyromonas gingivalis and Staphylococcus aureus tend to induce bone destruction and cause various inflammatory bone diseases including periodontal diseases, osteomyelitis, and septic arthritis. On the other hand, probiotic bacteria such as Lactobacillus and Bifidobacterium species can prevent bone loss. In addition, bacterial metabolites and various secretory molecules such as short chain fatty acids and cyclic nucleotides can also affect bone homeostasis. This review focuses on the regulation of osteoclast and osteoblast by MAMPs including cell wall components and secretory microbial molecules under in vitro and in vivo conditions. MAMPs could be used as potential molecular targets for treating bone-related diseases such as osteoporosis and periodontal diseases.

Streptococcus gordonii: Pathogenesis and Host Response to Its Cell Wall Components.

Streptococcus gordonii, a Gram-positive bacterium, is a commensal bacterium that is commonly found in the skin, oral cavity, and intestine. It is also known as an opportunistic pathogen that can cause local or systemic diseases, such as apical periodontitis and infective endocarditis. S. gordonii, an early colonizer, easily attaches to host tissues, including tooth surfaces and heart valves, forming biofilms. S. gordonii penetrates into root canals and blood streams, subsequently interacting with various host immune and non-immune cells. The cell wall components of S. gordonii, which include lipoteichoic acids, lipoproteins, serine-rich repeat adhesins, peptidoglycans, and cell wall proteins, are recognizable by individual host receptors. They are involved in virulence and immunoregulatory processes causing host inflammatory responses. Therefore, S.gordonii cell wall components act as virulence factors that often progressively develop diseases through overwhelming host responses. This review provides an overview of S. gordonii, and how its cell wall components could contribute to the pathogenesis and development of therapeutic strategies.

Enhanced biofilm formation of Streptococcus gordonii with lipoprotein deficiency.

Streptococcus gordonii is a commensal Gram-positive bacterium that acts as an opportunistic pathogen that can cause apical periodontitis, endocarditis, and pneumonia. Biofilm formation of bacteria is important for the initiation and progression of such diseases. Although lipoproteins play key roles in physiological functions, the role of lipoproteins of S. gordonii in its biofilm formation has not been clearly understood. In this study, we investigated the role of lipoproteins of S. gordonii in the bacterial biofilm formation using its lipoprotein-deficient strain (Δlgt). The S. gordonii Δlgt exhibited increased biofilm formation on the human dentin slices or on the polystyrene surfaces compared to the wild-type strain, while its growth rate did not differ from that of the wild-type. In addition, the S. gordonii Δlgt strain exhibited the enhanced LuxS mRNA expression and AI-2 production, which is known to be a positive regulator of biofilm formation, compared to the wild-type. Concordantly, the augmented biofilm formation of S. gordonii Δlgt was attenuated by an AI-2 inhibitor, D-ribose. In addition, lipoproteins from purified S. gordonii inhibited the biofilm formation of S. gordonii wild-type and Δlgt. Taken together, these results suggest that lipoprotein-deficient S. gordonii form biofilms more effectively than the wild-type strain, which might be related to the AI-2 quorum-sensing system.

Bacterial Lipoproteins Induce BAFF Production via TLR2/MyD88/JNK Signaling Pathways in Dendritic Cells.

B-cell activating factor (BAFF) plays a crucial role in survival, differentiation, and antibody secretion of B cells. Microbial products with B-cell mitogenic properties can indirectly promote expansion and activation of B cells by stimulating accessory cells, such as dendritic cells (DCs), to induce BAFF. Although bacterial lipoproteins are potent B-cell mitogen like lipopolysaccharides (LPSs), it is uncertain whether they can stimulate DCs to induce BAFF expression. Here, we evaluated the effect of bacterial lipoproteins on BAFF expression in mouse bone marrow-derived DCs. Lipoprotein-deficient Staphylococcus aureus mutant induced relatively low expression level of membrane-bound BAFF (mBAFF) and the mRNA compared with its wild-type strain, implying that bacterial lipoproteins can positively regulate BAFF induction. The synthetic lipopeptides Pam2CSK4 and Pam3CSK4, which mimic bacterial lipoproteins, dose-dependently induced BAFF expression, and their BAFF-inducing capacities were comparable to those of LPS in DCs. Induction of BAFF by the lipopeptide was higher than the induction by other microbe-associated molecular patterns, including peptidoglycan, flagellin, zymosan, lipoteichoic acid, and poly(I:C). Pam3CSK4 induced both mBAFF and soluble BAFF expression in a dose- and time-dependent manner. BAFF expression by Pam3CSK4 was completely absent in DCs from TLR2- or MyD88-deficient mice. Among various MAP kinase inhibitors, only JNK inhibitors blocked Pam3CSK4-induced BAFF mRNA expression, while inhibitors blocking ERK or p38 kinase had no such effect. Furthermore, Pam3CSK4 increased the DNA-binding activities of NF-κB and Sp1, but not that of C/EBP. Pam3CSK4-induced BAFF promoter activity via TLR2/1 was blocked by NF-κB or Sp1 inhibitor. Collectively, these results suggest that bacterial lipoproteins induce expression of BAFF through TLR2/MyD88/JNK signaling pathways leading to NF-κB and Sp1 activation in DCs, and BAFF derived from bacterial lipoprotein-stimulated DCs induces B-cell proliferation.

A Pilot Study of Chronological Microbiota Changes in a Rat Apical Periodontitis Model.

Apical periodontitis caused by microbial infection in the dental pulp is characterized by inflammation, destruction of the pulpal and periradicular tissues, and alveolar bone resorption. We analyzed the chronological changes in microbiota using a pyrosequencing-based approach combined with radiologic and histopathologic changes in a rat apical periodontitis model. During the three-week observation, the pulp and periapical area showed a typical progress of apical periodontitis. A total of 27 phyla, 645 genera, and 1276 species were identified. The root apex had a lower bacterial species diversity than the pulp chamber. Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria were dominant phyla in both the pulp chamber and root apex. Remarkably, bacterial communities showed a tendency to change in the root apex based on the disease progression. At the genus level, Escherichia, Streptococcus, Lactobacillus, Rodentibacter, and Bacteroidetes were dominant genera in the pulp chamber. The most abundant genera in the root apex were Bradyrhizobium, Halomonas, and Escherichia. The species Azospirillum oryzae increased in the pulp chamber, whereas the species Bradyrhizobium japonicum and Halomonas stevensii were highly observed in the root apex as the disease progressed. The experimental rat model of apical periodontitis demonstrated a relationship between the microbiota and the apical periodontitis progression.

Lipoteichoic acid of Enterococcus faecalis interferes with Porphyromonas gingivalis lipopolysaccharide signaling via IRAK-M upregulation in human periodontal ligament cells.

Periodontitis is a chronic inflammatory disease of the gum caused by infection with multispecies oral bacteria. Since the periodontopathic bacteria, Porphyromonas gingivalis together with Enterococcus faecalis are frequently detected in patients with a severe form of periodontitis, interactions between their virulence factors might play an important role in progression of the disease. P. gingivalis and E. faecalis possess lipopolysaccharide (Pg.LPS) and lipoteichoic acid (Ef.LTA), respectively, as the major virulence factors inducing inflammatory responses. However, the combinatorial effect of these virulence factors on chemokine expression was poorly understood. Here, we examined the interaction between Ef.LTA and Pg.LPS on IL-8 induction in human periodontal ligament (PDL) cells. Pg.LPS, but not Ef.LTA, induced IL-8 expression at both mRNA and protein levels, which was suppressed in the presence of Ef.LTA. Although Ef.LTA and Pg.LPS could stimulate Toll-like receptor 2 (TLR2), Ef.LTA did not interfere with Pg.LPS induced-TLR2 activation. However, Ef.LTA decreased Pg.LPS-induced phosphorylation of ERK, JNK, and p38 kinase. Furthermore, Ef.LTA suppressed Pg.LPS-induced IL-8 promoter activity as well as AP-1, NF-IL6 and NF-κB transcription factors, which are indispensable for IL-8 expression. Interestingly, Ef.LTA enhanced only IL-1 receptor-associated kinase-M (IRAK-M) expression among the tested negative regulators of TLR intracellular signaling cascades in the presence of Pg.LPS. In addition, silencing IRAK-M restored the decreased IL-8 expression by Ef.LTA in the presence of Pg.LPS. Collectively, these results suggest that Ef.LTA inhibits Pg.LPS-induced IL-8 expression in human PDL cells via inducing the expression of a negative regulator of TLR signaling cascades, IRAK-M.

Adiponectin Deficiency Triggers Bone Loss by Up-Regulation of Osteoclastogenesis and Down-Regulation of Osteoblastogenesis.

Osteoporosis and bone disorders related to the metabolic syndrome are often associated with adipokines secreted by adipocytes in bone. Adiponectin, a type of adipokine, is a regulator of immune responses and metabolic processes, but its role in bone biology remains uncertain. We investigated the role of adiponectin in bone metabolism using adiponectin-deficient mice in vivo and in vitro. Adiponectin-deficient mice exhibited reduced bone mass and increased adiposity. Adiponectin-deficient calvarial cells were prone to differentiate into adipocytes rather than osteoblasts. Although bone marrow macrophages (BMMs) from adiponectin-deficient mice had low osteoclastogenic potential as osteoclast precursors with increasing interferon regulatory factor 5 expression, under co-culture conditions of calvarial cells and BMMs, the enhanced receptor activator of nuclear factor κB ligand/osteoprotegerin (RANKL/OPG) ratio of adiponectin-deficient mesenchymal progenitor cells facilitated osteoclast differentiation. In addition, increased RANKL/OPG ratio was observed in the bone marrow extracellular fluid of adiponectin-deficient mice compared to that of wild-type mice. Notably, recombinant adiponectin treatment enhanced RANKL-induced osteoclast differentiation from BMMs but up-regulated OPG production in recombinant adiponectin-exposed calvarial cells, which inhibited osteoclast differentiation. Taken together, these results suggest that adiponectin plays an inhibitory role in bone metabolism through cross talk between precursor cells of both osteoclasts and osteoblasts by regulating RANKL/OPG ratio in the bone marrow microenvironment.

Propionate, together with triple antibiotics, inhibits the growth of Enterococci.

Enterococci are Gram-positive facultative anaerobic bacteria that colonize the oral cavity and gastrointestinal tract. Enterococcal infections, mainly caused by Enterococcus faecalis and Enterococcus faecium, include apical periodontitis, endocarditis, and bloodstream infections. Recently, vancomycinresistant Enterococci are considered major pathogens that are common but difficult to treat, especially in nosocomial settings. Moreover, E. faecalis is closely associated with recurrent endodontic infections and failed endodontic treatment. In this study, we investigated the effects of short-chain fatty acids (SCFAs), acetate, propionate, and butyrate, which are metabolites fermented by gut microbiota, on the growth of Enterococci. Enterococci were cultured in the presence or absence of acetate, propionate, or butyrate, and the optical density at 600 nm was measured to determine bacterial growth. The minimum inhibitory concentration/minimum bactericidal concentration test was conducted. Bacteria were treated with a SCFA, together with clinically used endodontic treatment methods such as triple antibiotics (metronidazole, minocycline, and ciprofloxacin) and chlorhexidine gluconate (CHX) to determine the effects of combination treatment. Of the SCFAs, propionate had a bacteriostatic effect, inhibiting the growth of E. faecalis in a dose-dependent manner and also that of clinical strains of E. faecalis isolated from dental plaques. Meanwhile, acetate and butyrate had minimal effects on E. faecalis growth. Moreover, propionate inhibited the growth of other Enterococci including E. faecium. In addition, combination treatment of propionate and triple antibiotics led to further growth inhibition, whereas no cooperative effect was observed at propionate plus CHX. These results indicate that propionate attenuates the growth of Enterococci, suggesting propionate as a potential agent to control Enterococcal infections, especially when combined with triple antibiotics.

Modulation of macrophage subtypes by IRF5 determines osteoclastogenic potential.

Bone-resorbing osteoclasts are differentiated from macrophages (MΦ) by M-CSF and RANKL. MΦ can be mainly classified into M1 and M2 MΦ, which are proinflammatory and anti-inflammatory, respectively, but little is known about their osteoclastogenic potential. Here, we investigated the osteoclastogenic potential of MΦ subtypes. When the two MΦ subtypes were differentiated into osteoclasts using M-CSF and RANKL, M2 MΦ more potently differentiated into osteoclasts than M1 MΦ. M2 MΦ generated with IL-4 or IL-10 also showed enhanced osteoclast differentiation compared with M1 MΦ induced by IFN-γ and lipopolysaccharide. In addition, robust bone-resorptive capacity and giant actin rings, which are features of mature osteoclasts, were observed in M2, but not M1 MΦ, under the osteoclast differentiation condition. Osteoclast differentiation was significantly increased in CD206+ M2 MΦ but not in CD86+ M1 MΦ. Compared with M1 MΦ, c-Fms and RANK were highly expressed in M2 MΦ. Enhanced osteoclastogenesis of M2 MΦ was mediated through sustained ERK activation, followed by efficient c-Fos and NFATc1 induction. Notably, the osteoclastogenic potential of M1 MΦ converted into M2 MΦ by exposure to M-CSF was higher than that of M2 MΦ converted into M1 MΦ by exposure to GM-CSF. Silencing IRF5, which is responsible for M1 MΦ polarization, increased osteoclast differentiation by enhancing c-Fms expression and activation of ERK, c-Fos, CREB, and NFATc1, which was inhibited by overexpression of IRF5. Collectively, M2 MΦ are suggested to be more efficient osteoclast precursors than M1 MΦ because of the attenuated expression of IRF5.

Lactobacillus plantarum Lipoteichoic Acid Inhibits Oral Multispecies Biofilm.

INTRODUCTION: Apical periodontitis is an inflammatory disease in the periradicular region of teeth that results from infection by multispecies bacterial biofilm residing in the root canal system. In this study, we investigated whether Lactobacillus plantarum lipoteichoic acid (Lp.LTA) could inhibit multispecies oral pathogenic bacterial biofilm formation. METHODS: Highly pure and structurally intact Lp.LTA was purified from L. plantarum. Actinomyces naeslundii, Lactobacillus salivarius, Streptococcus mutans, and Enterococcus faecalis were co-cultured to form oral multispecies biofilm in the presence or absence of Lp.LTA on culture plates or human dentin slices. Preformed biofilm was treated with or without Lp.LTA, followed by additional treatment with intracanal medicaments such as calcium hydroxide or chlorhexidine digluconate. Confocal microscopy and crystal violet assay were performed to determine biofilm formation. Biofilm on human dentin slices was visualized with a scanning electron microscope. RESULTS: Biofilm formation of multispecies bacteria on the culture dishes was dose-dependently reduced by Lp.LTA compared with the nontreatment control group. Lp.LTA also inhibited multispecies biofilm formation on the dentin slices in a dose-dependent manner. Interestingly, Lp.LTA was shown to reduce preformed multispecies biofilm compared with the nontreatment group. Moreover, Lp.LTA potentiated the effectiveness of the intracanal medicaments in the removal of preformed multispecies biofilm. CONCLUSIONS: These results suggest that Lp.LTA is a potential anti-biofilm agent for treatment or prevention of oral infectious disease, including apical periodontitis, which is mainly caused by multispecies bacterial biofilm.

Cyclic Dinucleotides Inhibit Osteoclast Differentiation Through STING-Mediated Interferon-ß Signaling.

Cyclic dinucleotides (CDNs), such as cyclic diadenylate monophosphate and cyclic diguanylate monophosphate, are commensal bacteria-derived second messengers in the gut that modulate bacterial survival, colonization, and biofilm formation. Recently, CDNs have been discovered to have an immunomodulatory activity by inducing the expression of type I interferon (IFN) through STING signaling pathway in macrophages. Because CDNs are possibly absorbed and delivered into the bone marrow, where bone-resorbing osteoclasts are derived from monocyte/macrophage lineages, CDNs could affect bone metabolism by regulating osteoclast differentiation. In this study, we investigated the effect of CDNs on the differentiation and function of osteoclasts and osteoblasts. When bone marrow-derived macrophages (BMMs) were differentiated into osteoclasts with macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL) in the presence of CDNs, the differentiation was inhibited by CDNs in a dose-dependent manner. In contrast, CDNs did not influence the differentiation of committed osteoclasts or osteoblast precursors. STING signaling pathway appeared to be critical for CDNs-mediated inhibition of osteoclast differentiation since CDNs induced the phosphorylation of TBK1 and IRF3, a representative feature of STING activation, and osteoclast differentiation was restored in STING knockdown BMMs with siRNA. Moreover, CDNs increased the mRNA expression of STING-meditated IFN-ß, which is a negative regulator of osteoclastogenesis. In addition, CDNs also induced the phosphorylation of STAT1, which mediates IFN-α/ß receptor (IFNAR) signal transduction. The inhibitory effects of CDNs on osteoclast differentiation were not observed in the presence of antibody blocking IFNAR or in macrophages derived from IFNAR1-/- mice. Experiments using a mouse calvarial implantation model showed that RANKL-induced bone resorption was inhibited by CDNs. Taken together, these results suggest that CDNs inhibit osteoclast differentiation and bone resorption through induction of IFN-ß via the STING signaling pathway. © 2019 American Society for Bone and Mineral Research.

Lipoteichoic acids of lactobacilli inhibit Enterococcus faecalis biofilm formation and disrupt the preformed biofilm.

Enterococcus faecalis, a Gram-positive bacterium commonly isolated in patients with refractory apical periodontitis, invades dentin tubules easily and forms biofilms. Bacteria in biofilms, which contribute to recurrent and/or chronic inflammatory diseases, are more resistant to antimicrobial agents than planktonic cells and easily avoid phagocytosis. Although Lactobacillus plantarum lipoteichoic acid (Lp.LTA) is associated with biofilm formation, the effect of Lp.LTA on biofilm formation by E. faecalis is not clearly understood. In this study, we investigated whether Lp.LTA inhibits E. faecalis biofilm formation. The degree of biofilm formation was determined by using crystal violet assay and LIVE/DEAD bacteria staining. The quantification of bacterial growth was determined by measuring the optical density at 600 nm with a spectrophotometer. Formation of biofilms on human dentin slices was observed under a scanning electron microscope. E. faecalis biofilm formation was reduced by Lp.LTA treatment in a dose-dependent manner. Lp.LTA inhibited biofilm development of E. faecalis at the early stage without affecting bacterial growth. LTA from other Lactobacillus species such as Lactobacillus acidophilus, Lactobacillus casei, or Lactobacillus rhamnosus GG also inhibited E. faecalis biofilm formation. In particular, among LTAs from various lactobacilli, Lp.LTA showed the highest inhibitory effect on biofilms formed by E. faecalis. Interestingly, LTAs from lactobacilli could remove the biofilm preformed by E. faecalis. These inhibitory effects were also observed on the surface of human dentin slices. In conclusion, Lactobacillus species LTA inhibits biofilm formation caused by E. faecalis and it could be used as an anti-biofilm agent for prevention or treatment against E. faecalis-associated diseases.