Introduction. Resistance to multiple antimicrobials is a global public health problem, so the development of new therapeutic alternatives is necessary. Objective. To evaluate the in vitro antibacterial effect of the aqueous extract of E. giganteum (horsetail), against Escherichia coli producing extended spectrum betalactamases (ESBL) and E. coli ATCC. Material and methods. Experimental controlled study. Non-probabilistic sample of three strains of E. coli ATCC and 12 strains of E. coli ESBL were faced with six percentage concentrations of the aqueous extract of E. giganteum (100, 50, 25, 12.5; 6.25 and 3,13 ); and three repetitions. Results. The minimum concentration of the aqueous extract of E. giganteum that inhibited 50 and 90% of observations (IMC 50 and IMC 90), compared to E. coli ATCC, was 34 and 70%; and against E. coli ESBL was 78 and 115%, respectively. Of nine observations on E. coli ATCC, six were inhibited at a concentration of 25%; and of the 36 observations on E. coli ESBL strains, 13 were inhibited at a concentration of 50%. The strains had an undifferentiated inhibitory behavior (p <0.05), against aqueous extract of E. giganteum. Conclusions. The aqueous extract of E. giganteum had an antibacterial effect against E. coli strains ATCC and ESBL, so it constitutes a future possibility of antimicrobial active ingredients for the treatment of infections by resistant bacteria. It is recommended to continue with preclinical studies of efficacy and safety in vitro and in vivo.