In vitro and in vivo antimicrobial activity of an active plant-based quadrocomplex for skin hygiene

Context: The current epidemiological situation causes a new surge of interest to perspective antimicrobial formulations for proper skin hygiene. Aims: To evaluate in vitro and in vivo the antimicrobial activity of a novel active quadrocomplex (QC) for skin hygiene based on Melaleuca alternifolia essential oil, eucalyptol, (-)-alpha-bisabolol and silver citrate. In addition, to analyze the phytochemical constituents by gas chromatography-mass spectrometry (GC-MS) and to assess the skin irritant potential after regular washing. Methods: The phytochemical analysis was performed using GC-MS. The Minimum Inhibitory Concentrations (MICs) were assessed using a colony-counting method with resazurin. The type of pharmacological interaction was investigated using a modern checkerboard assay. Results: The chemical composition exhibited 18 resolved phytochemicals with the highest concentrations for (-)-alpha-bisabolol (32.2%) and terpinen-4-ol (31.6%) through the GC-MS analysis. QC agents showed antimicrobial activity against Gram-positive and Gram-negative strains, with MIC values ranging from 1.25 to 40.00 mg/mL. The checkerboard assay demonstrated reduced MIC values for the combinations of QC agents against all reference strains. QC showed significant inhibition of Staphylococcus aureus growth with an average efficiency of 99.91% and Candida albicans 99.94 %. In vivo, the investigation of QC showed higher immediate and prolonged efficiency compared to base formulation (p<0.05). Dermatology evaluation indicated that QC added to the soap base did not affect the skin of hands during regular hand-washing and did not cause any negative effects on the skin. Conclusions: QC exhibits a balanced performance between antimicrobial activity and biological safety and can be considered a promising bioactive composition for regular hand hygiene application. Therefore, additional investigations are needed to study the mechanism of antimicrobial activity.