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Background: Recent declines in new antibiotic discovery and the increase in antibiotic resistance have resulted in failing against bacterial pathogens. To develop novel antibiotic therapies, medical researchers have begun to focus on traditional therapies. Combinational therapies consisting of medicinal plants and conventional antibiotics may reactivate current drugs that are otherwise ineffective against antibioticresistant bacteria. Terminalia sericea Burch. Ex DC, Terminalia prunioides Laws. and Terminalia gazensis Bak. f. are native South African plants with antimicrobial properties. However, combinations of Terminalia sericea, Terminalia prunioides and Terminalia gazensis with conventional antibiotics are yet to be evaluated for growth inhibitory activity against gastrointestinal pathogens. Methods: Terminalia spp. leaves were extracted with solvents of varying polarity. Antimicrobial screening was performed using disc diffusion and broth microdilution assays. Toxicity was measured using Artemia franciscana nauplii lethality assays. Results: All extracts (except the T. sericea extracts) showed low to moderate inhibitory activity against B. cereus and E. faecalis, A. faecalis, A. hydrophilia, S. sonnei and S. newport in both the disc diffusion and liquid dilution assay. Twenty-three extract/antibiotic combinations produced synergy, 26 were additive, 24 were non-interactive and seven were antagonistic. Most of the antagonist interactions occurred in combinations containing gentamicin. All extracts were either non-toxic or of low toxicity in the Artemia bioassay. Conclusion: Terminalia spp. extracts may mimic the actions of a resistance modifying agents, enhancing the activity of several antibiotics that are relatively ineffective alone. Further studies are required to identify the bioactive and potentiating components and their mechanisms of action. [ABSTRACT FROM AUTHOR]

Introduction: 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: In this study, Petalostigma spp. (native Australian medicinal plants) extracts were combined with a range of conventional antibiotics and tested against various microbial triggers of autoimmune diseases. The fruit and leaves were extracted separately with solvents of varying polarity and investigated for the ability to inhibit bacterial growth using disc diffusion and liquid dilution MIC techniques. Results: The methanolic and water extracts showed low to moderate inhibitory activity against several microbes. However, combinations of the mid-low polarity extracts with conventional antibiotics proved significantly more effective in inhibiting the growth of Proteus mirabilis and Acinetobacter baylyi (bacterial triggers of rheumatoid arthritis and multiple sclerosis respectively). In total, 14 different combinations proved to be synergistic. Notably, two antibiotics (chloramphenicol and erythromycin) with no inhibitory activity against P. mirabilis alone were shown to have substantial activity when tested in combination with Petalostigma spp. extracts. Conclusion: Although the mechanisms of synergy are still unclear, studies indicate that compounds within Petalostigma spp. may mimic the actions of resistance modifying agents, thus potentiating the activity of several antibiotics that are relatively ineffective alone. Isolation of these agents may be highly beneficial in drug design against several bacteria including the microbial triggers of rheumatoid arthritis and multiple sclerosis. [ABSTRACT FROM AUTHOR]