This study aimed to investigate the antibacterial activity of the water extract of Houttuynia cordata (HCWE) against multi-drug resistant (MDR) Escherichia coli isolates harboring the AcrA gene in order to determine its susceptibility for potential therapy. We examined 18 E. coli strains that exhibited resistance to at least three diﬀerent classes of antibiotics. The antibacterial eﬀect, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and transcriptional level of the AcrA gene were assessed by using the agar well diﬀusion technique, tube dilution method and real-time PCR analyses, respectively. The water extract of H.cordata had antibacterial activity against MDR E.coli isolates
tested with the highest and lowest zone diameters of inhibition (ZDI) of 29 and 13 mm at concentrations of 500 and 50 mg/ml, respectively. The MIC and MBC of HCWE against MDR E.coli isolates were 400 and 500 mg/ml, respectively. The expression of the AcrA gene was inhibited (0.39-, 0.29- and 0.16- fold) in a dose dependent manner by the HCWE when cultured with 25 mg/ml, 50 mg/ml and 100 mg/ml HCWE. Our results show HCWE has activity in vitro against MDR E.coli. Further studies are needed to determine if HCWE can be developed as a therapeutic agents against MDR E. coli.