Triterpene and Steroids from A. Rich (Onagraceae) Displayed Antimicrobial Activities and Synergistic Effects with Conventional Antibiotics.

Difficulties encountered in treating drug-resistant pathogens have created a need for new therapies. Synergistic combinations of antibiotics are considered as ideal strategies in combating clinical and multidrug-resistant (MDR) infections. In this study, the antimicrobial activities of triterpenes and steroids from A. Rich (Onagraceae) and their combined effects with antibiotics were assessed. The associations between plant constituents and antibiotics were evaluated by determining their fractional inhibitory concentrations (FICs). Sitost-5-en-3-ol formiate (), 5,6-dihydroxysitosterol (), and maslinic acid () were isolated from the ethyl acetate (EtOAc) extract. The EtOAc extract, compounds and (MIC = 16-128 g/mL) would be the best antibacterial and antifungal agents. The antimicrobial activities of amoxicillin were relatively weak against MDR and and significant against ATCC 25923. However, when used in association with plant constituents, it displayed an interesting synergistic effect. Among plant components-antibiotic combinations, the EtOAc extract and compound (steroid) showed a synergistic effect with amoxicillin/fluconazole against all the tested microorganisms whereas the association of compound (triterpenoid) and amoxicillin/fluconazole displayed an additive effect against and and a synergistic effect on , , , and ATCC 10231. Overall, the results of the present study demonstrated antibacterial and antifungal activities of extracts and compounds isolated from The findings of the current study also showed that the potency of antibiotics was improved when screened in combination with components, supporting the drug combination strategy to combat antimicrobial resistance.