Biofilms are resistant to antibiotics and are a major source of persistent and recurring infections by clinically important pathogens. Drugs used for biofilm-associated infections are limited because biofilm-embedded or biofilm-matrix bacteria are difficult to kill or eradiate. Therefore, many researchers are developing new and effective antibiofilm agents. Among them, antimicrobial peptides have an attractive interest in the development of antibiofilm agents. The present study evaluated the effects of 10 synthetic peptides on growth inhibition, inhibition of biofilm formation, and biofilm elimination in drug-resistant Pseudomonas aeruginosa. The planktonic cell growth and biofilm formation were dose-dependently inhibited by most of the peptides. WIK-14 eliminated preformed biofilm masses by removing carbohydrates, extracellular nucleic acids, proteins, and lipids constituting extracellular polymeric substances. The results demonstrated that WIK-14 and WIKE-14 peptides might provide novel therapeutic drugs to overcome multidrug resistance in biofilm-associated infections.

Antimicrobial peptides (AMPs) can combat drug-resistant bacteria with their unique membrane-disruptive mechanisms. This study aimed to investigate the antibacterial effects of several membrane-acting peptides with amphipathic structures and positional alterations of two tryptophan residues. The synthetic peptides exhibited potent antibacterial activities in a length-dependent manner against various pathogenic drug-resistant and susceptible bacteria. In particular, the location of tryptophan near the N-terminus of AMPs simultaneously increases their antibacterial activity and toxicity. Furthermore, the growth inhibition mechanisms of these newly designed peptides involve cell penetration and destabilization of the cell membrane. These findings provide new insights into the design of peptides as antimicrobial agents and suggest that these peptides can be used as substitutes for conventional antibiotics.

Profilins (PFNs) are actin monomer-binding proteins that function as antimicrobial agents in plant phloem sap. Although the roles of Arabidopsis thaliana profilin protein isoforms (AtPFNs) in regulating actin polymerization have already been described, their biochemical and molecular functions remain to be elucidated. Interestingly, a previous study indicated that AtPFN2 with high molecular weight (HMW) complexes showed lower antifungal activity than AtPFN1 with low molecular weight (LMW). These were bacterially expressed and purified to characterize the unknown functions of AtPFNs with different structures. In this study, we found that AtPFN1 and AtPFN2 proteins have LMW and HMW structures, respectively, but only AtPFN2 has a potential function as a molecular chaperone, which has never been reported elsewhere. AtPFN2 has better protein stability than AtPFN1 due to its higher molecular weight under heat shock conditions. The function of AtPFN2 as a holdase chaperone predominated in the HMW complexes, whereas the chaperone function of AtPFN1 was not observed in the LMW forms. These results suggest that AtPFN2 plays a critical role in plant tolerance by increasing hydrophobicity due to external heat stress.

Although considerable scientific research data is available for sepsis and cytokine storm syndrome, there is a need to develop new treatments or drugs for sepsis management. Antimicrobial peptides (AMPs) possess anti-bacterial and anti-inflammatory activity, neutralizing toxins such as lipopolysaccharides (LPS, endotoxin). Most AMPs have been designed as a substitute for conventional antibiotics, which kill drug-resistant pathogens. The present study aimed to determine the anti-inflammatory potential of 10 designed XIW (X: lysine, arginine, or glutamic acid) α-helical peptides in macrophages and a mouse model in the presence of LPS. Among them, WIKE-14, a peptide with a helix-to-helix structure, having the 12th amino acid substituted with glutamic acid, suppressed pro-inflammatory cytokines in RAW 264.7 macrophages. This reaction was mediated by the inhibition of the binding between LPS and macrophages. In addition, the WIKE-14 peptide exhibited a potent anti-inflammatory activity in mice ears and lungs inflamed using LPS. Thus, our results may provide useful insights for the development of anti-sepsis agents via the sequence and structure information of the WIKE-14 peptide.

Discovering new antifungal agents is difficult, since, unlike bacteria, mammalian and fungal cells are both eukaryotes. An efficient strategy is to consider new antimicrobial proteins that have variety of action mechanisms. In this study, a cDNA encoding Bacillus thuringiensis Vip3Aa protein, a vegetative insecticidal protein, was obtained at the vegetative growth stage; its antifungal activity and mechanism were evaluated using a bacterially expressed recombinant Vip3Aa protein. The Vip3Aa protein demonstrated various concentration- and time-dependent antifungal activities, with inhibitory concentrations against yeast and filamentous fungi ranging from 62.5 to 125 µg/mL and 250 to 500 µg/mL, respectively. The uptake of propidium iodide and cellular distributions of rhodamine-labeled Vip3Aa into fungal cells indicate that its growth inhibition mechanism involves its penetration within cells and subsequent intracellular damage. Furthermore, we discovered that the death of Candida albicans cells was caused by the induction of apoptosis via the generation of mitochondrial reactive oxygen species and binding to nucleic acids. The presence of significantly enlarged Vip3Aa-treated fungal cells indicates that this protein causes intracellular damage. Our findings suggest that Vip3Aa protein has potential applications in the development of natural antimicrobial agents.

Various proteins introduced into living modified organism (LMO) crops function in plant defense mechanisms against target insect pests or herbicides. This study analyzed the antifungal effects of an introduced LMO protein, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) from Agrobacterium sp. strain CP4 (CP4-EPSPS). Pure recombinant CP4-EPSPS protein, expressed in Escherichia coli, inhibited the growth of human and plant fungal pathogens (Candida albicans, C. tropicalis, C. krusei, Colletotrichum gloeosporioides, Fusarium solani, F. graminearum, and Trichoderma virens), at minimum inhibitory concentrations (MICs) that ranged from 62.5 to 250 µg/mL. It inhibited fungal spore germination as well as cell proliferation on C. gloeosporioides. Rhodamine-labeled CP4-EPSPS accumulated on the fungal cell wall and within intracellular cytosol. In addition, the protein induced uptake of SYTOX Green into cells, but not into intracellular mitochondrial reactive oxygen species (ROS), indicating that its antifungal action was due to inducing the permeability of the fungal cell wall. Its antifungal action showed cell surface damage, as observed from fungal cell morphology. This study provided information on the effects of the LMO protein, EPSPS, on fungal growth.