Arnica montana L. is renowned for its biological properties, including its antimicrobial effects, which are attributed to the presence of sesquiterpene lactones or flavonoids. The aim of this study was to assess the antimicrobial activity of ethanolic (EtE) and aqueous (AqE) extracts of Arnica montana L. against a reference strains of microbes, employing a double broth dilution method (concentration of 7.81-30000 µg/mL); identifiyng MICs and MBC/MFCs. Amoxicillin, nystatin, and 70% ethanol were used as positive controls. The MBC(MFC)/MIC ratios were used to assess the activity of EtE/AqE (<4 bactericidal/fungicidal; ≥4 -static). As a result, a differential antimicrobial activity was demonstrated in MIC=1000-2000 µg/mL and MIC=8000-16000 µg/mL for Gram(+) bacteria for EtE and AqE, respectively. EtE was more effective against Salmonella Typhimurium, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Proteus mirabilis (MIC=1000-2000 µg/mL), compared to AqE (MIC>16000 µg/mL). EtE was bactericidal against staphylococci and Enterobacteriaceae rods, while AqE was bactericidal against Bacillus cereus. Unlike EtE, which was effective to most Candida spp. (MIC=500-800 µg/mL), AqE had no antifungal properties.

This study suggests that the extracts and essences of A. montana have several beneficial properties such as antibacterial and antifungal effects. It highlights that essence extracts (EtEs) are more potent than aqueous extracts (AqEs) and can serve as natural antimicrobial agents. The raw material is mainly used in topical preparations due to its high toxicity, but can also be taken orally in low concentrations as a homeopathic remedy. The results of this study may pave the way for further research into activity against other microbial strains, and the development of new formulations for different applications. However, the challenge is to optimise solvent concentrations that are most suitable for biological experiments, particularly for alcohol extracts, which are good for solubilisation but can be cytotoxic if not carefully controlled.