The present invention relates to an antimicrobial peptide having an improved antibacterial effect through glutamic acid substitution and, more specifically, to a use of the antimicrobial peptide as an active ingredient in an antibacterial pharmaceutical composition, a food additive, a feed additive, an antiseptic composition, and an antibacterial quasi-drug composition. Not only does the antimicrobial peptide of the present invention exhibit significant antibacterial activity against gram-negative bacteria, but it also exhibits a significant synergistic effect when combinedly treated with antibiotics which have strong antibacterial activity only against gram-positive bacteria and has no or low antibacterial activity against gram-negative bacteria, thereby exhibiting excellent antibacterial effects on gram-positive bacteria, E. coli and Acinetobacter bacteria among gram-negative bacteria, and antibiotic-resistant strains thereof.
