Phenolic Profile, Antimicrobial Activity, and In Vivo Effects of Inula montbretiana DC. in the Galleria mellonella Model

This study aimed to evaluate the in vitro antimicrobial activities of chloroform (IMC), ethyl acetate (IMEA), and ethanol (IME) extracts obtained from the aerial parts of Inula montbretiana DC. by percolation. Antimicrobial activity against Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Pseudomonas aeruginosa, Proteus vulgaris, Klebsiella pneumoniae, and Candida albicans was assessed using agar well diffusion and microdilution methods. The in vivo effects of the extracts were investigated in Galleria mellonella larvae infected with C. albicans, S. epidermidis, or K. pneumoniae. In the microdilution assay, IMEA exhibited the broadest antimicrobial spectrum, with the lowest minimum inhibitory concentration (MIC) against C. albicans (0.11 mg/mL), followed by K. pneumoniae (0.21 mg/mL), whereas IME showed activity only against C. albicans. In the agar well diffusion assay, IMEA produced an inhibition zone of 12.31 ± 0.16 mm against S. epidermidis and that of IME was comparatively stronger against K. pneumoniae, with an inhibition zone of 14.43 ± 0.25 mm. In the infection model, IMC at 456 µg/mL and IMEA at 2120 µg/mL significantly improved survival in C. albicans-infected larvae, with approximately 40% survival at 120 h. IMC at 456 µg/mL also significantly improved survival in S. epidermidis-infected larvae, with approximately 40% survival at 120 h. The extracts showed limited efficacy against K. pneumoniae. HPLC-DAD analysis of IMEA and IME identified phenolic acids, including 4- hydroxybenzoic, chlorogenic, and caffeic acids, and flavonoids, including luteolin and apigenin. These findings demonstrate solvent-dependent antimicrobial activity and suggest protective effects of selected extracts in the G. mellonella infection model.