Antibacterial Action of Astaxanthin against Enterococcus faecalis: An In Silico and In Vitro Study

Aim:The aim of this study was to assess the antibacterial activity of 20% astaxanthin (ASX) solution against Enterococcus faecalis by disc diffusion assay and to evaluate the potential target sites against E. faecalis using the molecular docking method.Materials and methods: Molecular docking-the action of anti-E.faecalis was assessed using PyRx software version 0.8 with Auto Vina, and for agar disc diffusion assay, 20% ASX irrigating solution was prepared.Thirty Kirby-Bauer discs were soaked in group I: 1000 L of 3% sodium hypochlorite (NaOCl), group II: 1000 L of 2% chlorhexidine (CHX), group III: 1000 L of 20% ASX (n = 10 in each group).Discs were dried and placed in six Mueller-Hinton agar plates containing 10 L suspension of E. faecalis [Microbial Type Culture Collection (MTCC) 439].The agar plates were kept at room temperature for 2 hours for prediffusion of materials and then incubated at 37C for 24 hours and observed for zones of inhibition.Statistical analysis was done. Results:The results of molecular docking revealed that ASX targeted four potential sites against E. faecalis, namely nicotinamide adenine dinucleotide hydrogen (NADH), alanine racemase (AlaR), dihydrofolate reductase (DHFR), and acyl carrier protein (ACP).Disc diffusion assay showed that 3% NaOCl produced the maximum mean bacterial inhibition zone of 22 mm, followed by 2% CHX (17 mm) and 20% ASX (15.5 mm), which was statistically significant.Conclusion: Molecular docking study revealed that ASX possessed favorable binding scores to the four potential target sites, suggestive of beneficial anti-E.faecalis activity.According to the diffusion studies, NaOCl possessed the maximum anti-E.faecalis action followed by 2% CHX and 20% ASX.This study concluded that ASX can be used as a potential root canal irrigant against E. faecalis.Clinical significance: The current gold standard irrigant, NaOCl, exhibits certain undesirable biological properties that can be potentially harmful in cases of inadvertent extrusion into the periapical tissues.ASX could be a promising and biocompatible alternative to NaOCl due to its natural origin and favorable biological properties, especially in secondary root canal treatment cases.