Alkaline tolerance and biofilm formation of root canal isolates of Enterococcus faecalis: an in vitro study

Metformin reduced the alkaline resistance of Enterococcus faecalis against calcium hydroxide via Man-PTS EII: in vitro and in vivo studies

OBJECTIVES

The mannose phosphotransferase system (Man-PTS) plays crucial roles in the adaptive metabolic activity of Enterococcus faecalis (E. faecalis) in adverse environments. The aim of this study was to evaluate the role of Man-PTS in the alkaline resistance of E. faecalis against calcium hydroxide (CH) and the effect of metformin (Met) on the alkaline resistance of E. faecalis to CH.

MATERIALS AND METHODS

The regulatory role of Man-PTS EII in the alkaline resistance of E. faecalis was firstly investigated using a wild-type highly alkaline-resistant E. faecalis XS 003, standard ATCC 29212 and Man-PTS EIID gene deficient (△mptD) and overexpressing (+mptD)  strains of E. faecalis. RNA sequencing of Met-treated E. faecalis was performed to further validate the effect of Met on Man-PTS. The effect of Met on CH resistance of E. faecalis was verified by evaluating the survival, membrane potential and permeability, intracellular pH and ATP, and the expression of Man-PTS EII and membrane transporter-related genes of E. faecalis. The effect of Met on the ability of CH to remove E. faecalis biofilm on the dentin surface was also tested. The in vivo therapeutic effect of Met plus CH (CHM) was further investigated in a rat apical periodontitis model induced by E. faecalis XS 003.

RESULTS

Man-PTS EII significantly promoted the survival ability of E. faecalis in CH and enhanced its resistance to CH. The inhibition of Man-PTS EII by Met resulted in reduced alkaline resistance of E. faecalis in the presence of CH, while also enhancing the antimicrobial properties of CH against E. faecalis biofilm on dentin. Additionally, Met plus CH showed the synergistically promoted intra-canal E. faecalis infection control and healing of periapical lesion in rats.

CONCLUSIONS

Met could significantly reduce the alkaline resistance of E. faecalis against CH through the modulation of Man-PTS EII, and improved the antibacterial effect of CH against E. faecalis infection both in vitro and in vivo.

CLINICAL RELEVANCE

Met could significantly enhance the ability of CH to control E. faecalis infection through reducing the alkaline resistance of E. faecalis.

Strategies and mechanisms targeting Enterococcus faecalis biofilms associated with endodontic infections: a comprehensive review

Enterococcus faecalis is one of the main microorganisms that infects root canals, ranking among the most prevalent microorganisms associated with endodontic treatment failure. Given its pervasive presence in persistent endodontic infections, the successful elimination of Enterococcus faecalis is crucial for effective endodontic treatment and retreatment. Furthermore, Enterococcus faecalis can form biofilms - defense structures that microbes use to fight environmental threats. These biofilms confer resistance against host immune system attacks and antibiotic interventions. Consequently, the presence of biofilms poses a significant challenge in the complete eradication of Enterococcus faecalis and its associated disease. In response, numerous scholars have discovered promising outcomes in addressing Enterococcus faecalis biofilms within root canals and undertaken endeavors to explore more efficacious approaches in combating these biofilms. This study provides a comprehensive review of strategies and mechanisms for the removal of Enterococcus faecalis biofilms.

Synergistic antibacterial effect of ginsenoside Rh2 and calcium hydroxide on Enterococcus faecalis

Treatment of root canal infections becomes more challenging due to the extremely high tolerance of Enterococcus faecalis (E. faecalis) to calcium hydroxide (Ca(OH)2). Ginsenoside is a Chinese herbal extract that has been proven to have antimicrobial properties and synergistic activities. And this study evaluated the antibacterial activity of ginsenoside Rh2 in combination with Ca(OH)2 against E. faecalis and its preliminary mechanism of action. Broth microdilution method, checkerboard dilution method, time-inhibition curve, drug resistance assays, scanning electron microscopy, and biofilm inhibition and removal assays indicated that Rh2 in combination with Ca(OH)2 exhibited potent antibacterial activity against E. faecalis. Rh2 exerted significant in vitro antibacterial activity against E. faecalis, with a minimum inhibitory concentration (MIC) of 3.125 μg/mL and minimum bactericidal concentration (MBC) of 6.25 μg/mL, and significantly enhanced the susceptibility of E. faecalis to Ca(OH)2 (FICI = 0.5). Furthermore, cell membrane permeability assays, surface hydrophobicity assays, ATPase activity assays, and intra-biofilm extracellular polysaccharides (EPS) assays revealed that Rh2 and Ca(OH)2 synergistically inhibit bacteria mainly by increasing membrane permeability. Ultimately, cytotoxicity assays showed that Rh2 exhibited only low toxicity, the half maximal inhibitory concentration (IC50) of Rh2 was 19.75 μg/mL. This study confirmed the synergistic antibacterial activities of Rh2 and Ca(OH)2 against E. faecalis. Our findings indicate that the Rh2 and Ca(OH)2 combination may be a promising alternative approach to treating root canal infections.

Lipopeptide biosurfactant as a potential root canal irrigation agent: Antimicrobial and anti-biofilm evaluation

OBJECTIVES

Lipopeptide Biosurfactant (LB) is a bacteria derived compound able to reduce surface tension between water and hydrophobic substances and exhibit antimicrobial and anti-biofilm properties. This study aimed to investigate the antimicrobial and anti-biofilm effect of a Lipopeptide Biosurfactant (LB) on Enterococcus faecalis, and its potential use in root canal treatment, either as a standalone irrigation solution or in conjunction with sodium hypochlorite (NaOCl).

METHODS

LB was extracted from Bacillus clausii isolate and the dry extract was diluted in deionized water. The antimicrobial effect of LB against planktonic E. faecalis was evaluated by determining the Minimal Inhibitory Concentration (MIC50). The anti-biofilm effect was evaluated by Minimal Biofilm Inhibitory Concentration (MBIC50) and Minimal Biofilm Eradication Concentration (MBEC50) assays on biofilm grown on dentin specimen surface. To evaluate the effectiveness of LB as a single irrigation solution and as a pre-irrigation prior to NaOCl, live and dead bacterial cells were quantified using Confocal Laser Scanning Microscopy (CLSM), and cell biomass was assessed.

RESULTS

LB exhibited an MIC50 and MBIC50 of 100 ppm, with an MBEC50 of 1000 ppm, resulting in 52.94 % biofilm inhibition and 60.95 % biofilm eradication on dentin specimens. The effectiveness was concentration-dependent, at 500 ppm, LB demonstrated comparable antimicrobial efficacy to 2.5 % NaOCl. Pre-irrigation with LB resulted in lower biofilm biomass compared to NaOCl alone.

CONCLUSION

Pre-irrigation with LB enhanced the antimicrobial effect when followed by NaOCl irrigation. Consequently, LB shows promise as both a standalone root canal irrigation solution and as an adjunct to NaOCl in root canal treatment.

CLINICAL SIGNIFICANCE

The study highlights the potential of Lipopeptide Biosurfactant (LB) as an environmentally friendly irrigation solution for root canal treatment, demonstrating potent antimicrobial and anti-biofilm properties against Enterococcus faecalis. LB exhibits concentration-dependent efficacy comparable to 2.5 % NaOCl and can be used as a standalone irrigation solution or in conjunction with NaOCl.

Moringa oleifera: A Review of the Pharmacology, Chemical Constituents, and Application for Dental Health

Moringa oleifera L., commonly known as Kelor in Indonesia and miracle tree in English, has a rich history of utilization for medicinal, nutritional, and water treatment purposes dating back to ancient times. The plant is renowned for its abundance of vitamins, minerals, and various chemical constituents, making it a valuable resource. Among its notable pharmacological properties are its effectiveness as an anti-diabetic, anti-diarrheal, anti-helmintic, anti-leishmanial, anti-fungal, anti-bacterial, anti-allergic, anti-cancer, anti-inflammatory, and anti-oxidant agent. In this comprehensive review, we delve into the extensive pharmacological applications and phytochemical constituents of M. oleifera and its application in dental health.

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.

Enterococcus faecalis V583 cell membrane protein expression to alkaline stress

Enterococcus faecalis is able to adapt to alkaline conditions and is commonly recovered from teeth in which endodontic treatment has failed. The role that E. faecalis membrane proteins play in survival strategies to extreme alkaline conditions is unclear. We grew E. faecalis V583 in a chemostat at pH 8 and 11 at one-tenth the organism’s relative maximum growth rate. Following membrane shaving, isotope-coding protein labels were added at the peptide level to samples and then combined. The relative proportion of membrane proteins were identified using LC-ESI mass spectrometry and MaxQuant analysis. Ratios of membrane proteins were log₂ transformed, with proteins deviating by more than 1 SD of the mean considered to be up- or down-regulated. A total of six proteins were up-regulated in pH 11 including: EF0669 (polysaccharide biosynthesis family); EF1927 (glycerol uptake facilitator), and EF0114 (glycosyl hydrolase). A total of five proteins were down-regulated including: EF0108 (C4-dicarboxylate transporter); EF1838 (PTS system IIC component); EF0456 (PTS system IID component); and EF0022 (PTS mannose-specific IID component). In extreme alkaline conditions, the membrane proteins of E. faecalis seem to be involved in a shift of carbohydrate metabolism from the PTS system to glycerol, which supports the formation of a protective capsule protecting the cell.