Evaluation of Plant-Guided Strategies Against Clinical Multidrug-Resistant Pathogens: Preliminary Phytochemical Screening, Antioxidant Capacity, and Antibacterial/Antibiofilm Activity of Rosa canina and Colchicum autumnale Extracts

Background/Objectives: Antimicrobial resistance, an evolutionarily entrenched microbial capacity amplified by extensive antibiotic exposure, has increased the burden of difficult-to-treat infections caused by priority pathogens such as Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus. In this study, we assessed whether phytochemical-rich extracts from fully ripe Rosa canina pseudo-fruits (WF) and fully developed Colchicum autumnale flowers (CA) can provide combined antioxidant, antibacterial, and antibiofilm effects against multidrug-resistant clinical isolates. Methods: Plant materials were processed using seven extraction systems spanning non-polar to polar conditions (n-hexane, ethyl acetate, n-butanol, aqueous, 40% ethanol, 60% ethanol, and enzyme-assisted hydrolysis). Fractions were quantified for total phenolics, flavonoids, and tannins, evaluated for antioxidant capacity (DPPH and FRAP), tested for antibacterial activity (disc diffusion and MIC/MBC), and assessed for inhibition of early biofilm attachment. Differences among extraction methods and fractions were analyzed using standard comparative statistics (group comparisons across solvents/fractions), and relationships between chemical composition and bioactivity were examined using correlation-based analysis. Results: Extraction strategy emerged as the main determinant of bioactivity across endpoints. The WFE/ENZ fraction maximized phytochemical recovery (TPC 203.34 ± 11.55 mg GAE/g DW; TFC 35.67 ± 3.06 mg QE/g DW; TTC 53.00 ± 2.65 mg TAE/g DW) and showed strong antioxidant performance (DPPH IC50 33.60 ± 0.02 μg/mL; FRAP A700 1.90 ± 0.010 at 250 μg/mL). Antibacterial effects were strongest in polar fractions, particularly hydroethanolic and enzyme-assisted extracts, while n-hexane fractions were consistently weakest. Across eight clinical isolates and three reference strains, MIC values ranged from 0.04875 to 6.25 mg/mL for WF extracts and 0.0975–12.5 mg/mL for CA extracts. In the biofilm model, suppression of early attachment was most consistent for CAE/E60–ENZ and WFE/E40–E60–ENZ fractions. Conclusions: Correlation analysis indicated that antibacterial potency aligned primarily with flavonoid levels in R. canina pseudo-fruits and with tannin content in C. autumnale material. Overall, these results support hydroethanolic and enzyme-assisted extraction as rational strategies to enrich polyphenol-dense fractions with convergent antioxidant, antibacterial, and antibiofilm activity, reinforcing plant-derived matrices as a structured discovery space for developing complementary antimicrobial solutions beyond conventional antibiotics. Notably, this is among the first studies to evaluate the antibacterial potential of C. autumnale plant material in this context and to comprehensively assess R. canina pseudo-fruit extracts against multidrug-resistant clinical.