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.

OBJECTIVES: 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.

METHODS: 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.

RESULTS: 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<0.05) in the expression level of acrA was seen in the presence of ciprofloxacin in clones pre-treated with plant extract or matrine for 36h. Accumulation of ciprofloxacin enhanced 2.8- and 2-fold following addition of matrine and plant extract, respectively, in these clones.

CONCLUSIONS: Alkaloid extract of local S. alopecuroides and matrine have anti-pump activity; further investigations are necessary to elucidate their exact mechanisms of action.