Exploration of the mechanisms of biofilm formation byEnterococcus faecalisin glucose starvation environments

Triple threat: how diabetes results in worsened bacterial infections

Diabetes mellitus, characterized by impaired insulin signaling, is associated with increased incidence and severity of infections. Various diabetes-related complications contribute to exacerbated bacterial infections, including hyperglycemia, innate immune cell dysfunction, and infection with antibiotic-resistant bacterial strains. One defining symptom of diabetes is hyperglycemia, resulting in elevated blood and tissue glucose concentrations. Glucose is the preferred carbon source of several bacterial pathogens, and hyperglycemia escalates bacterial growth and virulence. Hyperglycemia promotes specific mechanisms of bacterial virulence known to contribute to infection chronicity, including tissue adherence and biofilm formation. Foot infections are a significant source of morbidity in individuals with diabetes and consist of biofilm-associated polymicrobial communities. Bacteria perform complex interspecies behaviors conducive to their growth and virulence within biofilms, including metabolic cross-feeding and altered phenotypes more tolerant to antibiotic therapeutics. Moreover, the metabolic dysfunction caused by diabetes compromises immune cell function, resulting in immune suppression. Impaired insulin signaling induces aberrations in phagocytic cells, which are crucial mediators for controlling and resolving bacterial infections. These aberrancies encompass altered cytokine profiles, the migratory and chemotactic mechanisms of neutrophils, and the metabolic reprogramming required for the oxidative burst and subsequent generation of bactericidal free radicals. Furthermore, the immune suppression caused by diabetes and the polymicrobial nature of the diabetic infection microenvironment may promote the emergence of novel strains of multidrug-resistant bacterial pathogens. This review focuses on the "triple threat" linked to worsened bacterial infections in individuals with diabetes: (i) altered nutritional availability in diabetic tissues, (ii) diabetes-associated immune suppression, and (iii) antibiotic treatment failure.

Triton X-100 counteracts antibiotic resistance of Enterococcus faecalis: An in vitro study

OBJECTIVES

The high prevalence of antibiotic-resistant bacteria poses a threat to the global public health. The appropriate use of adjuvants to restore the antimicrobial activity of antibiotics against resistant bacteria could be an effective strategy for combating antibiotic resistance. In this study, we investigated the counteraction of Triton X-100 (TX-100) and the mechanisms underlying the antibiotic resistance of Enterococcus faecalis (E. faecalis).

METHODS

Standard, wild-type (WT), and induced antibiotic-resistant E. faecalis strains were used in this study. In vitro antibacterial experiments were conducted to evaluate the antimicrobial activities of gentamicin sulfate and ciprofloxacin hydrochloride in the presence and absence of 0.02 % TX-100 against both planktonic and biofilm bacteria. Transcriptomic and untargeted metabolomic analyses were performed to explore the molecular mechanisms of TX-100 as an antibiotic adjuvant. Additionally, membrane permeability, membrane potential, glycolysis-related enzyme activity, intracellular adenosine triphosphate (ATP), and expression levels of virulence genes were assessed. The biocompatibility of different drug combinations was also evaluated.

RESULTS

A substantially low TX-100 concentration improved the antimicrobial effects of gentamicin sulfate or ciprofloxacin hydrochloride against antibiotic-resistant E. faecalis. Mechanistic studies demonstrated that TX-100 increased cell membrane permeability and dissipated membrane potential. Moreover, antibiotic resistance and pathogenicity of E. faecalis were attenuated by TX-100 via downregulation of the ABC transporter, phosphotransferase system (PTS), and ATP supply.

CONCLUSIONS

TX-100 enhanced the antimicrobial activity of gentamicin sulfate and ciprofloxacin hydrochloride at a low concentration by improving antibiotic susceptibility and attenuating antibiotic resistance and pathogenicity of E. faecalis.

CLINICAL SIGNIFICANCE

These findings provide a theoretical basis for developing new root canal disinfectants that can reduce antibiotic resistance.

Bad to the bone? - Genomic analysis of Enterococcus isolates from diverse environments reveals that most are safe and display potential as food fermentation microorganisms

Enterococci comprise a group of lactic acid bacteria (LAB) with considerable potential to serve as food fermentation microorganisms. Unfortunately, enterococci have received a lot of negative attention, due to the occurrence of pathogenic and multidrug resistant strains. In this study, we used genomics to select safe candidates among the forty-four studied enterococcal isolates. The genomes of the forty-four strains were fully sequenced and assessed for presence of virulence and antibiotic resistance genes. Nineteen isolates belonging to the species Enterococcus lactis, Enterococcus faecium, Enterococcus durans, and Enterococcus thailandicus, were deemed safe from the genome analysis. The presence of secondary metabolite gene clusters for bacteriocins was assessed, and twelve candidates were found to secrete antimicrobial compounds effective against Listeria monocytogenes isolated from cheese and Staphylococcus aureus. Physiological characterization revealed nineteen industrial potentials; all strains grew well at 42 °C and acidified 1.5 hours faster than their mesophilic counterpart Lactococcus lactis, with which they share metabolism and flavor forming ability. We conclude that a large fraction of the examined enterococci were safe and could serve as excellent food fermentation microorganisms with inherent bioprotective abilities.

Coaggregated E. faecalis with F. nucleatum regulated environmental stress responses and inflammatory effects

To investigate the cell-cell interactions of intergeneric bacterial species, the study detected the survival of Enterococcus faecalis (Ef) under monospecies or coaggregation state with Fusobacterium nucleatum subsp. polymorphum (Fnp) in environmental stress. Ef and Fnp infected the human macrophages with different forms (Ef and Fnp monospecies, Ef-Fnp coaggregates, Ef + Fnp cocultures) for exploring the immunoregulatory effects and the relevant molecular mechanisms. Meanwhile, the transcriptomic profiles of coaggregated Ef and Fnp were analyzed. Ef was shown to coaggregate with Fnp strongly in CAB within 90 min by forming multiplexes clumps. Coaggregation with Fnp reinforced Ef resistance against unfavorable conditions including alkaline, hypertonic, nutrient-starvation, and antibiotic challenges. Compared with monospecies and coculture species, the coaggregation of Ef and Fnp significantly facilitates both species to invade dTHP-1 cells and aid Ef to survive within the cells. Compared with coculture species, dual-species interaction of Ef and Fnp significantly decreased the levels of pro-inflammatory cytokines IL-6, TNF-α, and chemokines MCP-1 secreted by dTHP-1 cells and lessened the phosphorylation of p38, JNK, and p65 signaling pathways. The transcriptome sequencing results showed that 111 genes were differentially expressed or Ef-Fnp coaggregated species compared to Ef monospecies; 651 genes were differentially expressed for Fnp when coaggregation with Ef. The analysis of KEGG pathway showed that Ef differentially expressed genes (DEGs) were enriched in quorum sensing and arginine biosynthesis pathway; Fnp DEGs were differentially concentrated in lipopolysaccharide (LPS) biosynthesis, biofilm formation, and lysine degradation pathway compared to monospecies. KEY POINTS: • Coaggregated with Fnp aids Ef's survival in environmental stress, especially in root canals after endodontic treatment. • The coaggregation of Ef and Fnp may weaken the pro-inflammatory response and facilitate Ef to evade killed by macrophages. • The coaggregation between Ef and Fnp altered interspecies transcriptional profiles.

Enhanced in vitro antibacterial effect against Enterococcus faecalis by using both low-dose cetylpyridinium chloride and silver ions

BACKGROUND

Enterococcus faecalis (E. faecalis) is frequently isolated from root canals with failed root canal treatments. Due to the strong ability of E. faecalis to resist many often-used antimicrobials, coping with E. faecalis infections remains a challenge. The aim of this study was to investigate the synergistic antibacterial effect of low-dose cetylpyridinium chloride (CPC) and silver ions (Ag⁺) against E. faecalis in vitro.

METHODS

The minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and the fractional inhibitory concentration index (FICI) were used to confirm the existence of the synergic antibacterial activity between low-dose CPC and Ag⁺. Colony-forming unit (CFU) counting, time-killing curve and dynamic growth curve were used to evaluate the antimicrobial effects of CPC and Ag⁺ combinations against planktonic E. faecalis. Four weeks biofilms were treated with drug-contained gels to determine the antimicrobial effect on biofilm-resident E.faecalis, and the integrity of E.faecalis and its biofilms were observed by FE-SEM. CCK-8 assays was used to test the cytotoxicity of CPC and Ag⁺ combinations on MC3T3-E1 cells.

RESULTS

The results confirmed the synergistic antibacterial effect of low-dose CPC and Ag⁺ against both planktonic and 4-week biofilm E. faecalis. After the addition of CPC, the sensitivity of both planktonic and biofilm-resident E. faecalis to Ag⁺ improved, and the combination showed good biocompatibility on MC3T3-E1 cells.

CONCLUSIONS

Low-dose CPC enhanced the antibacterial ability of Ag⁺ against both planktonic and biofilm E.faecalis with good biocompatibility. It may be developed into a novel and potent antibacterial agent against E.faecalis, with low toxicity for root canal disinfection or other related medical applications.

Differences in Virulence Factors and Antimicrobial Susceptibility of Uropathogenic Enterococcus spp. Strains in a Rural Area of Uganda and a Spanish Secondary Hospital

Enterococcus faecalis and Enterococcus faecium have become two of the most important agents of nosocomial diseases due to their constantly growing resistance. Enterococcal infections are associated with biofilms, which are intrinsically sensitive to antimicrobials. The main goal of this study was to compare and relate their capacity to form biofilm and their antimicrobial sensitivity, as well as their virulence factors and their implicated genes, of strains isolated from patients with urinary tract infection (UTI) in a rural hospital in Uganda and a secondary hospital in Spain. A prospective study was conducted with 104 strains of E. faecalis and E. faecium isolated from patients with suspected UTI and who presented leukocyturia at the Saint Joseph Kitgum hospital (Uganda) and at the Hospital Universitario Principe de Asturias (Spain). All microorganisms were identified in Spain by MALDI-TOF mass spectrometry. Antimicrobial susceptibility studies were carried out using the Vitek^® 2 system (Biomériux, France). The biofilm formation capacity was studied by photospectrometry. Phenotypic and genotypic virulence factors were studied in all cases by PCR or expression techniques. In Uganda, we found a higher incidence of E. faecium (65.3%, n = 32), contrary to the situation found in Spain where most of the bacteria found belonged to E. faecalis (92.7%, n = 51). All E. faecalis strains were found to have very low levels of resistance to ampicillin, imipenem, and nitrofurantoin. However, E. faecium exhibited more than 25% resistance to these antibiotics. Although the esp gene has been shown in the results obtained to be an important initial agent in biofilm formation, we have also demonstrated in this study the intervention of other genes when esp is not present, such as the ace1 gene. No statistically significant relationships were found between the presence of agg and gelE genes and increased biofilm formation. The significant difference between the incidence of E. faecalis and E. faecium and biofilm formation, between samples from Spain and Uganda, shows us very different profiles between countries.

Role of Enterococcus faecalis in refractory apical periodontitis: from pathogenicity to host cell response

BACKGROUND

Refractory apical periodontitis (RAP) is an oral infectious disease characterised by persistent inflammation, progressive alveolar bone destruction, and delayed bone healing. RAP has received increasing attention, because it cannot be cured after repeated root canal therapies. The aetiology of RAP is related to the complex interplay between the pathogen and its host. However, the exact pathogenesis of RAP remains unclarified and includes several factors, such as microorganism immunogenicity, host immunity and inflammation, and tissue destruction and repair. Enterococcus faecalis is the dominant pathogen involved in RAP, and has evolved multiple strategies to ensure survival, which cause persistent intraradicular and extraradicular infections.

OBJECTIVE

To review the crucial role of E. faecalis in the pathogenesis of RAP, and open new avenues for prevention and treatment of RAP.

METHODS

The PubMed and Web of Science databases were searched for pertinent publications, employing the search terms "Enterococcus faecalis", "refractory apical periodontitis", "persistent periapical periodontitis", "pathogenicity", "virulence", "biofilm formation", "dentine tubule", "immune cell", "macrophage", and "osteoblast".

RESULTS AND CONCLUSION

Besides its high pathogenicity due to various virulence mechanisms, E. faecalis modulates the macrophage and osteoblast responses, including regulated cell death, cell polarisation, cell differentiation, and inflammatory response. An in-depth understanding of the multifaceted host cell responses modulated by E. faecalis will help to design potential future therapeutic strategies and overcome the challenges of sustained infection and delayed tissue healing in RAP.

In vitro antibacterial effects of photodynamic therapy against Enterococcus faecalis in root canals of deciduous teeth

OBJECTIVE

This study aimed at evaluating the in vitro antibacterial efficacy of photodynamic therapy (PDT) on planktonic E. faecalis and its biofilm in the root canal of infected deciduous teeth.

METHODS

Forty root canals of maxillary deciduous anterior teeth were enlarged up to #35 K-file and inoculated with E. faecalis for 21 days. The root canals were randomly assigned into four groups (n = 10): The normal saline group (control), 1% NaClO group, PDT group, and the 1% NaClO + PDT group. Paper point samples were obtained at baseline (S1) and after treatment (S2). The colony-forming units (CFU) were counted, and the bacterial growth rate calculated. From each subgroup, 5 samples were randomly selected after treatment and a scanning laser confocal microscope (CLSM) used to determine the distribution of dead / living bacteria on the biofilm surface of each subgroup. A scanning electron microscope (SEM) was used to observe bacterial morphologies in the root canal walls of the remaining 5 samples in each subgroup. The Kruskal-Wallis test and Dunn test with boferroni adjustment were used to analyze the effect of the different treatment techniques on the E. faecalis in root canals.

RESULTS

Compared to the saline group, PDT significantly reduced bacterial counts in the root canal (p < 0.05). The CFU counts were lowest (p < 0.05) in the 1% NaClO and in 1% NaClO + PDT groups. The rate of bacterial death on the surface of the biofilm in the PDT group was significantly increased after treatment (p < 0.05), and the rate of bacterial death was highest in 1%NaClO group and 1%NaClO + PDT group (p < 0.05).

CONCLUSION

PDT has an antibacterial activity against E. faecalis in the root canal of deciduous teeth. Its activity against planktonic E. faecalis is better than the activity on the intact biofilm. The antibacterial activity of PDT on E. faecalis in root canals of deciduous teeth is lower compared to that of 1% NaClO.

Thiol- and Disulfide-Containing Vancomycin Derivatives Against Bacterial Resistance and Biofilm Formation

Antibiotic-resistant and biofilm-associated infections constitute a rapidly growing issue. Use of the last-resort antibiotic vancomycin is under threat due to the increasing appearance of vancomycin-resistant bacteria as well as the formation of biofilms. Herein, we report a series of novel vancomycin derivatives carrying thiol- and disulfide-containing moieties. The new compounds exhibited enhanced antibacterial activity against a broad range of bacterial strains, including vancomycin-resistant microbes and Gram-negative bacteria. Moreover, all obtained derivatives demonstrated improved antibiofilm formation activity against VanB-resistant Enterococcus compared to vancomycin. This work establishes a promising strategy for combating drug-resistant bacterial infections or disrupting biofilm formation and advances the knowledge on the structural optimization of antibiotics with sulfur-containing modifications.

Fsr quorum sensing system modulates the temporal development of Enterococcus faecalis biofilm matrix

Quorum sensing (QS) is a cell-to-cell communication process that regulates major pathogenic attributes in bacteria including biofilm formation, secretion of virulence factors, and antimicrobial resistance. The two-component Fsr-QS system of the nosocomial pathogen Enterococcus faecalis controls the production of extracellular gelatinase that contributes to biofilm development by enhancing the release of nucleic acids into the biofilm matrix. However, the contribution of this system to the deposition of other biofilm matrix components such as polysaccharides and proteins remains unknown. Using wild type and mutant strains, we discovered that biofilm formation was attenuated by inactivation of the Fsr system or its downstream gelatinase production. Inactivation of the Fsr system caused a modest, yet significant reduction in biofilm metabolic activity without affecting cell counts. Inactivation of the QS-signal sensor FsrC and response regulator FsrA resulted in decreased extracellular polysaccharides and proteins in biofilms in a temporal manner. Irrespective of biofilm age, eDNA levels were reduced in the gelatinase mutant strain. Our results collectively suggest that the Fsr system contributes to the temporal deposition of polysaccharides and proteins into the extracellular polymeric matrix (EPS) of E. faecalis biofilm, without affecting bacterial viability. This understanding of the role of the Fsr-QS system in biofilm development may reveal a novel target to develop effective antibiofilm agents to tackle E. faecalis-mediated infections such as in dental root canals, heart valves, and surgical sites.

Synergistic effects of silver ions and metformin against enterococcus faecalis under high-glucose conditions in vitro

Background

This study aimed to evaluate the synergistic antibacterial activities of silver ions (Ag⁺) and metformin hydrochloride (Met) against Enterococcus faecalis (E. faecalis) under normal or high-glucose conditions.

Results

The minimum inhibitory concentration, minimum bactericidal concentration, growth curves, and colony-forming units were used to evaluate the antibacterial effects of Ag⁺ and Met on planktonic E. faecalis in Brain Heart Infusion broth with or without additional glucose. The influences of Ag⁺ and Met on four weeks E. faecalis biofilm on human dentin slices was also tested. Cytotoxicity was tested on MC3T3-E1 osteoblastic cells using CCK-8 assays. The results indicated that E. faecalis showed higher resistance to drug treatment under high-glucose conditions. Ag⁺ (40 μg/mL) plus Met (3.2% or 6.4%) showed enhanced antibacterial activities against both planktonic E. faecalis and biofilm on dentin slices, with low cytotoxicity.

Conclusions

Met enhanced the bactericidal effects of Ag⁺ against both planktonic and biofilm E. faecalis under normal or high-glucose conditions with low cytotoxicity. Further molecular studies are needed to be conducted to understand the mechanisms underlying the synergistic activity between Met and Ag⁺.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-021-02291-2.

Research on the Biofilm Formation of Staphylococcus aureus after Cold Stress

Staphylococcus aureus is a common food pathogen and has a strong tolerance to environmental stress. Here, the biofilm formation of S. aureus strains after cold stress for 24 weeks were investigated. It was found that the biofilm formation of S. aureus CICC 21600, CICC 22942, W1, W3, and C1 cells was enhanced after cold stress for 20 weeks. What is more, the mRNA levels of the clfA, icaA, icaB, icaC or icaD genes in these strains were increased for >2-fold. The increased gene transcription levels were consistent with the increase in the polysaccharide content in the biofilm matrix of these S. aureus strains after cold stress. Meanwhile, hydrophobicity and the adhesion proteins also played a role in the formation of biofilms. The biofilm of S. aureus cells can be effectively degraded by snailase and proteinase K (125 µg/mL + 20 µg/mL) mixture. In summary, S. aureus frozen at -20 °C for 12 to 20 weeks is still a potential hazard. Food factory equipment should be cleaned in a timely manner to avoid outbreaks of foodborne pathogenic bacteria due to contamination.

Proteomic analysis of an Enterococcus faecalis mutant generated against the exposure to silver nanoparticles

INTRODUCTION

Nanoparticles (NPs) have been widely studied as an alternative to antibiotic use due to their antimicrobial properties at lower concentrations. Enterococcus faecalis is a facultative Gram-positive microorganism inhabiting the gastrointestinal tract of humans and animals. It can also be present in other environments such as the oral cavity, water, sewage, soil and food.

AIMS

We evaluated whether E. faecalis could develop resistance to silver NPs (AgNPs) after exposure to sublethal concentrations of the NPs.

METHODS AND RESULTS

Proteomic analyses revealed that different pathways were activated during the acquired resistance under sublethal concentrations, and selected genes were validated by qPCR.

CONCLUSIONS

The results of this study showed that E. faecalis is capable of generating resistance to AgNPs.

SIGNIFICANCE AND IMPACT OF THE STUDY

To avoid the generation of resistance against AgNPs, future use of these NPs should be combined with other NPs prepared with different metals to prevent the dissemination of resistant strains.

Disinfection of Root Canals with Laser-Activated Irrigation, Photoactivated Disinfection, and Combined Laser Techniques: An Ex Vivo Preliminary Study

Objective: This study aimed to evaluate the efficacy of laser-activated irrigation using photon-induced photoacoustic streaming (PIPS^®) and photoactivated disinfection (PAD) techniques and their combination to improve penetration and activation of toluidine blue in the endodontic space of teeth experimentally infected with Enterococcus faecalis. Materials and methods: Twenty-seven extracted single-root teeth were instrumented, sterilized, and infected with E. faecalis and divided into seven groups of three teeth each: Group A [sodium hypochlorite (NaClO) 5% hand irrigation], Group B [NaClO 5% hand irrigation+ethylenediaminetetraacetic acid (EDTA)+NaClO 5% activated by PIPS], Group C (EDTA+NaClO 5% activated by PIPS), Group D (toluidine blue activated by PAD), Group E (toluidine blue activated by PIPS and PAD), Group F (NaClO 5% hand irrigation+toluidine blue activated by PAD), and Group G (NaClO 5% hand irrigation+toluidine blue activated by PIPS and PAD). Finally, positive and negative group controls were prepared. The presence of biofilms after the treatments was assessed by the BioTimer assay. PIPS was performed with an Er:YAG laser (2940 nm, LightWalker, Fotona^® d.o.o., Slovenia) at 20 mJ, 15 Hz, 0.3 W, and 50-μs pulse duration. PAD was performed with a 635 nm diode laser (Smart M, Lasotronix^®, Poland) at 400 mW in continuous wave (CW). Results: When NaClO was used, significant decontamination (p ≤ 0.05) was obtained in all experimental groups with respect to the positive control, other than Group G. Irrigation with EDTA+NaClO activated by PIPS produced a higher level of decontamination than Group A (p ≤ 0.05). Significant results in reducing biofilm load compared with the control and Group A were observed when NaClO was coupled with toluidine blue activated by PAD (p ≤ 0.05). Conclusions: Disinfection of root canals can be obtained using a combination of different irrigants, photosensitizers, and activation protocols. EDTA+NaClO using the PIPS protocol and toluidine blue activated by PAD (both preceded by NaClO irrigation) can be considered effective tools. The possibility of replacing NaClO with toluidine blue, whatever the method of activation, should be further investigated.

Genotype, biofilm formation ability and specific gene transcripts characteristics of endodontic Enterococcus faecalis under glucose deprivation condition

OBJECTIVE

To study the relationship between the specific gene and biofilm formation ability of seven wild type Enterococcus faecalis (E. faecalis) under glucose deprivation conditions.

DESIGN

Wild type E. faecalis (3RC, 5RC, 25RC, 31RC, 33RC, 37RC, 58RC) extracted from the teeth with persistent apical periodontitis were cultured under glucose deprivation conditions and then resequenced. The biofilm formation ability was compared using primary adherence assay, confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The transcriptional level of biofilm formation-related genes (ace, gelE, efa, esp and fsrB) were detected.

RESULTS

Genomic resequencing showed that 3RC and 58RC (Class B) were similar, while 5RC, 25RC, 31RC, 33RC and 37RC (Class A) were similar. Based on primary adherence assay, CLSM and SEM results, biofilm formation ability of Class B strains was lower, while Class A strains were higher when compared with control group (0.25 % glucose). Furthermore, compared with control group (0.25 % glucose), the transcriptional levels of ace, efa and fsrB genes were upregulated in all strains; the transcriptional levels of gelE were downregulated in Class B strains, upregulated in Class A strains; the transcriptional levels of esp of Class B strains were downregulated, while upregulated in 25RC, 31RC and 37RC (Class A), and not observed in 5RC and 33RC.

CONCLUSION

The genotypes of wild type E. faecalis of different persistent periapical periodontitis teeth are different. The genotype differences and the transcription levels of related virulence genes (ace, gelE, efa, esp and fsrB) are related to the biological phenotype.

Endodontic-Like Oral Biofilms as Models for Multispecies Interactions in Endodontic Diseases

Oral bacteria possess the ability to form biofilms on solid surfaces. After the penetration of oral bacteria into the pulp, the contact between biofilms and pulp tissue may result in pulpitis, pulp necrosis and/or periapical lesion. Depending on the environmental conditions and the availability of nutrients in the pulp chamber and root canals, mainly Gram-negative anaerobic microorganisms predominate and form the intracanal endodontic biofilm. The objective of the present study was to investigate the role of different substrates on biofilm formation as well as the separate and collective incorporation of six endodontic pathogens, namely Enterococcus faecalis, Staphylococcus aureus, Prevotella nigrescens, Selenomonas sputigena, Parvimonas micra and Treponema denticola into a nine-species "basic biofilm". This biofilm was formed in vitro as a standard subgingival biofilm, comprising Actinomyces oris, Veillonella dispar, Fusobacterium nucleatum, Streptococcus anginosus, Streptococcus oralis, Prevotella intermedia, Campylobacter rectus, Porphyromonas gingivalis, and Tannerella forsythia. The resulting endodontic-like biofilms were grown 64 h under the same conditions on hydroxyapatite and dentin discs. After harvesting the endodontic-like biofilms, the bacterial growth was determined using quantitative real-time PCR, were labeled using fluorescence in situ hybridization (FISH) and analyzed by confocal laser scanning microscopy (CLSM). The addition of six endodontic pathogens to the "basic biofilm" induced a decrease in the cell number of the "basic" species. Interestingly, C. rectus counts increased in biofilms containing E. faecalis, S. aureus, P. nigrescens and S. sputigena, respectively, both on hydroxyapatite and on dentin discs, whereas P. intermedia counts increased only on dentin discs by addition of E. faecalis. The growth of E. faecalis on hydroxyapatite discs and of E. faecalis and S. aureus on dentin discs were significantly higher in the biofilm containing all species than in the "basic biofilm". Contrarily, the counts of P. nigrescens, S. sputigena and P. micra on hydroxyapatite discs as well as counts of P. micra and T. denticola on dentin discs decreased in the all-species biofilm. Overall, all bacterial species associated with endodontic infections were successfully incorporated into the standard multispecies biofilm model both on hydroxyapatite and dentin discs. Thus, future investigations on endodontic infections can rely on this newly established endodontic-like multispecies biofilm model.

Matrix metalloprotease-1 inhibits and disrupts Enterococcus faecalis biofilms

Enterococcus faecalis is a major opportunistic pathogen that readily forms protective biofilms leading to chronic infections. Biofilms protect bacteria from detergent solutions, antimicrobial agents, environmental stress, and effectively make bacteria 10 to 1000-fold more resistant to antibiotic treatment. Extracellular proteins and polysaccharides are primary components of biofilms and play a key role in cell survival, microbial persistence, cellular interaction, and maturation of E. faecalis biofilms. Degradation of biofilm components by mammalian proteases is an effective antibiofilm strategy because proteases are known to degrade bacterial proteins leading to bacterial cell lysis and growth inhibition. Here, we show that human matrix metalloprotease-1 inhibits and disrupts E. faecalis biofilms. MMPs are cell-secreted zinc- and calcium-dependent proteases that degrade and regulate various structural components of the extracellular matrix. Human MMP1 is known to degrade type-1 collagen and can also cleave a wide range of substrates. We found that recombinant human MMP1 significantly inhibited and disrupted biofilms of vancomycin sensitive and vancomycin resistant E. faecalis strains. The mechanism of antibiofilm activity is speculated to be linked with bacterial growth inhibition and degradation of biofilm matrix proteins by MMP1. These findings suggest that human MMP1 can potentially be used as a potent antibiofilm agent against E. faecalis biofilms.

Effect of the luxS gene on biofilm formation and antibiotic resistance by Salmonella serovar Dublin

Biofilms are communities of bacterial cells that serve to protect them from external adverse influences and enhance bacterial resistance to antibiotics and sanitizers. Here, we studied the regulatory effects of glucose and sodium chloride on biofilm formation in Salmonella serovar Dublin (S. Dublin). To analyze expression levels of the quorum sensing gene luxS, we created a luxS knockout mutant. Also, antimicrobial resistance, hydrophobicity and autoinducer-2 (AI-2) activity of both the wild-type (WT) and the mutant strain were investigated. Our results revealed that glucose was not essential for S. Dublin biofilm formation but had an inhibitory effect on biofilm formation when the concentration was over 0.1%. NaCl was found to be indispensable in forming biofilm, and it also exerted an inhibitory effect at high concentrations (>1.0%). Both the WT and the mutant strains displayed significant MIC growth after biofilm formation. An increase of up to 32,768 times in the resistance of S. Dublin in biofilm phonotype against antibiotic (ampicillin) compared to its planktonic phonotype was observed. However, S. Dublin luxS knockout mutant only showed slight differences compared to the WT strain in the antimicrobial tests although it displayed better biofilm-forming capacity than the WT strain. The mutant strain also exhibited higher hydrophobicity than the WT strain, which was a feature related to biofilm formation. The production of the quorum sensing autoinducer-2 (AI-2) was significantly lower in the mutant strain than in the WT strain since the LuxS enzyme, encoded by the luxS gene, plays an essential role in AI-2 synthesis. However, the limited biofilm-forming ability in the WT strain indicated AI-2 was not directly related to S. Dublin biofilm formation. Furthermore, gene expression analysis of the WT and mutant strains revealed upregulation of genes related to biofilm stress response and enhanced resistance in the luxS mutant strain, which may provide evidence for the regulatory role of the luxS gene in biofilm formation.

Micro-CT evaluation of apical delta morphologies in human teeth

The apical delta is an intricate system within the root canal and incompletely debridement may affect the long-term prognosis of root canal therapy. The aim of the present study is to investigate the morphologic features of apical deltas in human teeth with micro-computed tomography (micro-CT) using a centreline-fitting algorithm. One hundred and thirty-six apical deltas were detected in 1400 teeth. Molars had more apical deltas (15.8%) than anterior teeth (6.3%). In maxillary molars, the mesiobuccal root had a significantly higher prevalence of apical delta than the palatal root or the distobuccal root. The median vertical distance of the apical delta was 1.87 mm with 13% more than 3 mm. The median diameter and length of the apical delta branches were 132.3 and 934.5 μm. Apical delta branches were not straight with cross-sectional shapes being non-circular. These morphological features of apical delta may complicate debridement of the infected root canal system.

Identification and functional characterization of the putative polysaccharide biosynthesis protein (CapD) of Enterococcus faecium U0317

Most bacterial species produce capsular polysaccharides that contribute to disease pathogenesis through evasion of the host innate immune system and are also involved in inhibiting leukocyte killing. In the present study, we identified a gene in Enterococcus faecium U0317 with homologies to the polysaccharide biosynthesis protein CapD that is made up of 336 amino acids and putatively catalyzes N-linked glycosylation. A capD deletion mutant was constructed and complemented by homologous recombination that was confirmed by PCR and sequencing. The mutant revealed different growth behavior and morphological changes compared to wild-type by scanning electron microscopy, also the capD mutant showed a strong hydrophobicity and that was reversed in the reconstituted mutant. For further characterization and functional analyses, in-vitro cell culture and in-vivo a mouse infection models were used. Antibodies directed against alpha lipotechoic acid (αLTA) and the peptidyl-prolyl cis-trans isomerase (αPpiC), effectively mediated the opsonophagocytic killing in the capD knock-out mutant, while this activity was not observed in the wild-type and reconstituted mutant. By comparison more than 2-fold decrease was seen in mutant colonization and adherence to both T24 and Caco2 cells. However, a significant higher bacterial colonization was observed in capD mutant during bacteremia in the animal model, while virulence in a mouse UTI (urinary tract infection) model, there were no obvious differences. Further studies are needed to elucidate the function of capsular polysaccharide synthesis gene clusters and its involvement in the disease pathogenesis with the aim to develop targeted therapies to treat multidrug-resistant E. faecium infections.

Implant Placement in Failed Endodontic Sites: A Review

Dental implants may fail to osseointegrate in sites of endodontic failure. This may occur as a result colonization by various anaerobic and facultative bacterial species. If an implant is placed in a site where vegetative bacteria are residing, the implant may fail to integrate if a bacterial colonization proceeds coronally. If the implant apical cortical bone is thin or if there is an apical fenestration, the colonization may proceed through the thin or nonexistent bone through the covering mucosa, relieving inflammatory pressure to create an apical (retrograde) peri-implantitis. Enterococcus faecalis may be the prime culprit in these types of implant failures. After thorough debridement, the implant may be immediately placed after extraction of an endodontically failed tooth, and the patient treated with an appropriate antibiotic. Alternatively waiting for postextraction healing and subsequent implant placement can be done. Nevertheless, either way may allow for the formation of bacterial vegetative forms or biofilms. The implant surface may be colonized when the surface is exposed to the bacteria. Thorough debridement is crucial. Nonetheless, organisms may persist. Randomized controlled trials are needed to elucidate this issue.