Efficacy of antimicrobial peptides (AMPs) against Escherichia coli and bacteria morphology change after AMP exposure

In recent years, bacterial drug resistance has become a major health concern worldwide owing to the limited efficacy of some traditional antibiotics after long-term usage. Here, to search for potent bacteriostatic agents, six cationic antimicrobial peptides (AMPs) were investigated. L-GL13K, D-GL13K, MSI-594, indolicidin, Ib-M6 and nisinA-S29A were selected to study their bactericidal efficiency and the antibacterial mechanisms against Escherichia coli (E. coli). In addition to half-maximal inhibitory concentration (IC₅₀) and minimum inhibitory concentration (MIC) determinations using the standard method, the initial bacterial growth profiles at 4 h of AMP exposure were used to study the possible antibacterial mechanisms. The AMP-treated E. coli exhibited collapsed cell walls and various nanosized and microsized pores on the bacterial surface, which led to transmembrane channels and pore formation. Among the studied peptides, MSI-594, D-GL13K, and L-GL13K (in decreasing order) were identified as superior bactericidal agents, which may be attributed to the suitable conformational structure and surface charge during the interaction between these AMPs and bacteria.