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An increase in antibiotic resistance and a corresponding decrease in antimicrobial discovery have directed researchers towards alternative therapies, including plant based medicines. However, synergistic combinations of plant extracts with conventional antibiotics are a far more effective approach in overcoming resistance and potentiating the activity of antibiotics that are otherwise ineffective against resistant bacterial strains. Methods: The antibacterial activity of Rosa canina (Rosehip) extracts was investigated by disc diffusion and quantified by liquid dilution and solid phase MIC assays. The extracts were also combined with a range of conventional antibiotics and tested against various microbial triggers of autoimmune diseases. The ΣFIC values obtained from these assays were used to determine the class of combinational effects and isobologram analysis was used to determine the ideal synergistic ratio(s). Toxicity was evaluated by Artemia nauplii and HDF cell line viability. Results: The methanolic, water and ethyl acetate extracts showed good inhibitory activity against several microbes. However, combinations of the methanolic or aqueous extracts with conventional antibiotics proved significantly more effective in inhibiting the growth of Proteus vulgaris, Klebsiella pneumonia and Acinetobacter baylyi (bacterial triggers of rheumatoid arthritis, ankylosing spondylitis and multiple sclerosis respectively). In total, 4 synergistic interactions were noted. Notably, the methanolic extract restored significant growth inhibitory activity to chloramphenicol and tetracycline when tested in combination, thereby restoring their activity. Conclusion: Although the mechanisms of synergy are still unclear, studies indicate that compounds within R. canina may mimic the actions of resistance modifying agents, thus potentiating the activity of two antibiotics that are relatively ineffective alone. Isolation of these agents may be beneficial in drug design against several bacteria including the microbial triggers of rheumatoid arthritis, ankylosing spondylitis and multiple sclerosis. [ABSTRACT FROM AUTHOR]