Effect of total alkaloid extract of local Sophora alopecuroides on minimum inhibitory concentration and intracellular accumulation of ciprofloxacin, and acrA expression in highly resistant Escherichia coli clones

•Herbal plants, including Sophora spp., distributed worldwide are rich in secondary metabolites such as alkaloids.•Sophora alopecuroides alkaloid extract and matrine reduced the ciprofloxacin MIC in highly resistant E. coli clones.•The alkaloid extract and matrine enhanced intracellular accumulation of ciprofloxacin in highly resistant E. coli clones.•The alkaloid extract and matrine reduced expression of genes encoding components of AcrAB–TolC efflux pump, such as acrA.•The alkaloid extract and matrine can be used as EPIs to increase the efficiency of antibiotics against MDR isolates. Multidrug-resistant phenotypes in Gram-negative bacteria such as Escherichia coli mainly result from overexpression of the AcrAB–TolC efflux pump. Efflux pump inhibitors may be obtained from plant extracts, such as alkaloid extract of Sophora spp. The aims of this study were to evaluate the antibacterial and anti-pump potential of local Sophora alopecuroides total alkaloid extract and commercial matrine in combination with ciprofloxacin in highly resistant E. coli clones. Alkaloid extract of S. alopecuroides seeds was prepared by acid–base solution and chloroform extraction. The percentage of matrine in this extract was measured by high-performance liquid chromatography (HPLC). Minimum inhibitory concentrations (MICs) of the extract and matrine in combination with ciprofloxacin were determined by the microbroth dilution method. The anti-pump activity of these combined materials was measured by ciprofloxacin accumulation assay and real-time PCR. The alkaloid extract contained 31.2% matrine. A synergistic interaction [fractional inhibitory concentration index (FICI)=0.13] was seen between the extract (1.56mg/mL) and ciprofloxacin (1μg/mL) in highly resistant E. coli clones. A significant decrease (P