Background: The widespread use of antibiotics has led to the emergence of many drug-resistant strains; thus, the development of new antibacterial drugs is essential with antimicrobial peptides becoming the focus of research. This study assessed the antibacterial effect of a novel antimicrobial peptide, named LL-1 onEscherichia coli(E.coli) by determining the minimum inhibitory concentration (MIC) and the antibacterial curve. The interaction between LL-1 andE. coliDNA was then detected by nucleic acid gel electrophoresis. The effect of LL-1 on theE. colicell membrane was assessed by detecting the leakage of β-galactosidase, nucleic acid and protein. The influence of LL-1 on the intracellular ATP ofE. coliwas analysed by determining the concentration of intracellular ATP. Finally, the bacteria and colonies ofE. colitreated with LL-1 were observed using scanning and transmission electron microscopy.Results: The results suggested that the MIC value was 3.125 µg/ml, and the antibacterial effect was dose-dependent. LL-1 dose-dependently combined withE. coliDNA. LL-1 resulted in the leakage of intracellular β-galactosidase, nucleic acid and protein, and decreased intracellular ATP concentrations ofE. coli. Two MIC of LL-1 causedE. colito shrink, resulting in a rough surface, plasmolysis, and bacterial adhesion.Conclusion: This study indicated that LL-1 had a good bactericidal effect onE. coliby mainly increasing the permeability of the cell membrane, leading to leakage of the intracellular content. This will lay the foundation for an in-depth study on the antibacterial mechanism of LL-1 againstE. coliand its clinical application.

Liang X, et al. J Vet Sci. 2019 Oct;21:e80. https://doi.org/10.4142/jvs.2020.21.e80

Background: The recent emergence of antibiotic-resistant strains of bacteria has increased the need to develop effective alternatives to antibiotics. Antimicrobial peptides have been considered as a promising product with several advantages. Results: In this present study, we identified a novel cecropin from the armyworm, Mythimna separata (armyworm cecropin 1, AC-1) by transcriptome sequencing and multi-sequence alignment analysis. The AC-1 precursor comprised 63 amino acid residues, containing a conserved cleavage site of the signal peptide, Ala₂₃-Pro₂₄, while the mature AC-1 included 39 amino acid residues. Chemically synthesized AC-1 exhibited low hemolytic activity against chicken red blood cells, low cytotoxicity against swine testis cells, and effective antimicrobial activity against Salmonella, Escherichia coli, Klebsiella pneumonia, and Pseudomonas aeruginosa. Its antimicrobial activity against Salmonella remained after incubation for 1 h at 100 °C or in 250 mM NaCl, KCl, or MgCl₂ solution, implying good thermal- and salt-resistant stabilities. The bactericidal effect of AC-1 on E. coli gradually increased with increasing AC-1 concentration, resulting in deformation, severe edema, cytolysis, cell membrane damage, and reducing intracellular electron density. Additionally, recombinant AC-1 protein expressed in E. coli was digested by enterokinase protease to obtain AC-1, which showed similar antimicrobial activity against E. coli to chemically synthesized AC-1. Conclusions: This study identified a novel antimicrobial peptide that may represent a potential alternative to antibiotics.

Channel catfish (Ictalurus punctatus) is a widely consumed freshwater fish known for its nutritional value but is highly prone to spoilage. This study investigated the quality changes of catfish muscle tissue under refrigeration and freezing through physicochemical, metabolomic, and microbial analyses. Results revealed that sensory scores decreased significantly during storage, with frozen samples maintaining similar scores to refrigerated ones after extended periods. Protein degradation and lipid oxidation, indicated by TVB-N and TBARS levels, were more pronounced during prolonged freezing. Metabolomic profiling identified 261 differential metabolites under long-term freezing, including elevated phosphatidylcholines, sphingomyelins, and disrupted amino acid pathways. Shifts in spoilage-associated microbial genera, such as Pseudomonas, and the correlations between microbial genera and specific metabolites, such as Methylobacterium with methylmalonic acid, highlighted microbial-driven spoilage processes. These findings provided a comprehensive understanding of quality deterioration during storage, guiding the development of enhanced preservation strategies for aquatic products.