Animal antimicrobial peptides (AMPs), known as broad-spectrum and high-efficiency antibacterial activity, are important effector molecules in innate immune system. AMPs not only have antimicrobial, antiviral and antitumor effects but also exhibit important effects in vivo, such as anti-inflammatory response, recruiting immune cells, promoting epithelial damage repair, and promoting phagocytosis of bacteria. However, research on the application of AMPs is incomplete and controversial. This review mainly introduces the classification of AMPs, biological functions, as well as the mechanisms of action, expression rules, and nutrition regulation from three perspectives, aiming to provide important information for the application of AMPs.

Transportation is common in cats and often causes stress and intestinal disorders. Antimicrobial peptides (AMPs) exhibit a broad spectrum of antibacterial activity, and they may have the capacity for antioxidant and immune regulation. The objective of this study was to investigate the effects of dietary supplementation with AMPs on stress response, gut microbiota and metabolites of cats that have undergone transport stress. A total of 14 Ragdoll cats were randomly allocated into 2 treatments: basal diet (CON) and a basal diet supplemented with 0.3% AMPs. After a 6-week feeding period, all cats were transported for 3 h and, then, fed for another week. The results show that the diarrhea rate of cats was markedly reduced by supplementation with AMPs throughout the trial period (p < 0.05). In addition, AMPs significantly reduced serum cortisol and serum amyloid A (p < 0.05) and increased apolipoprotein 1 after transportation (p < 0.05). Moreover, AMPs reduced the level of inflammatory factors in the serum caused by transportation stress, including tumor necrosis factor-alpha (TNF-α) and interleukin-1 beta (IL-1β) (p < 0.05). The AMPs enhanced the activities of glutathione peroxidase (p < 0.01) and superoxide dismutase (p < 0.05). Furthermore, cats fed AMPs had higher levels of branched chain fatty acids (BCFAs) and a relative abundance of Blautia and a lower relative abundance of Negativibacillus after transportation (p < 0.05). The serum metabolome analysis further revealed that AMPs markedly regulated lipid metabolism by upregulating cholic acid expression. In conclusion, AMP supplementation alleviated oxidative stress and inflammatory response in transportation by regulating the gut microbiota and metabolites, thereby relieving stress-induced diarrhea and supporting gut and host health in cats.

Infection caused by Staphylococcus aureus, especially methicillin-resistant S. aureus (MRSA), is very common in communities and hospitals, which poses a great challenge to human health. Therefore, increasing attention has been paid to finding effective antimicrobial agents. Mansonone F is a natural compound which has an oxaphenalene skeleton and anti-S. aureus activity, but its sources are limited and its synthesis is difficult. Thus, IG1, a C9-substituent mansonone F analog, was assessed for its activity against Staphylococcus aureus and its mechanism of action was investigated. Antimicrobial susceptibility assays showed that IG1 has strong antibacterial activity against S. aureus, including MRSA, with minimum inhibitory concentrations (MICs) ranging from 0.5 to 2 μg/mL, which were very close to those of vancomycin, and these changed little, even with an increase in the amount of the inoculum. To further explore the antibacterial properties of IG1, time–kill experiments were conducted. Compared with vancomycin and moxifloxacin, treatment with different concentrations of IG1 reduced the viability of organisms in a very similar manner and the reduction was not significant, which indicated that IG1 is a potentially strong anti-S. aureus agent. Finally, the antibacterial mechanism was analyzed, with flow cytometric analysis revealing that IG1 treatment resulted in a time-dependent decrease in the DNA content of S. aureus. Transmission electron microscopy (TEM) analysis showed that very few dividing cells could be found and the cell wall was damaged in the field of IG1-treated cells. These results indicate that IG1 is a potential new antibacterial agent against S. aureus, including MRSA.

In order to improve the bioavailability of baicalin, this article prepared for α-zein loaded with baicalin composites (α-zein@BA) by pH driven method and they were characterized using scanning electron microscopy, infrared spectroscopy, and measurement of particle size distribution in water solution phase techniques. The digestive behavior and antioxidant activity of composites before and after simulating gastrointestinal fluid in vitro were studied as well. At the same time, molecular dynamics simulation techniques were used to reveal the molecular mechanism behind the formation of the composite between the two. The results indicated that the composites of α-zein@BA were observed to be approximately spherical under a scanning electron microscope, and their particle size was mainly distributed in the range of 94.55-145.10 μm in aqueous solution, whose encapsulation efficiency of baicalin was (86.61 ± 0.71) %. Infrared spectroscopy analysis indicated that α-zein and baicalin mainly formed complexes through hydrogen bonding, electrostatic and hydrophobic interactions. The measurement results of baicalin residue in simulated digestion of gastric and intestinal fluids in vitro are as follows: α-zein@BA > Baicalin, while both significantly increased in the gastric digestion stage (P < 0.05) and significantly decreased in the intestinal digestion stage (P < 0.05). Molecular dynamics simulation studies have shown that baicalin has a promoting effect on protein structural stability, and protein 158SER and GLN196 were mainly formed hydrogen bonds with it, while hydrophobic interactions were mainly manifested between non-polar amino acids such as PHE201 and PRO200. This study indicates that α-zein and baicalin can form stable composites, improving the bioavailability of baicalin.

Sour soup is a traditional plant-based fermented food from Qiandongnan Prefecture, Guizhou Province, China. It is divided into two types: white sour soup and red sour soup. White sour soup is made by semi-anaerobic fermentation of oryza sativa var. glutinosa washing water in earthenware jars for 7-10 days. Red sour soup is prepared by crushing and mixing solanum lycopersicum, red capsicum annuum, and zingiber officinale with oryza sativa var. glutinosa washing water at a ratio of 3:1:0.5:5, followed by semi-anaerobic fermentation for 10-15 days. To date, no study has systematically compared the bacterial community and functional differences between the two types of sour soup. In this study, six samples of each type were analyzed by 16 S rRNA gene sequencing and PICRUSt2 functional prediction. The results showed that their community structures were significantly separated (p < 0.05). White sour soup was dominated by Proteobacteria (93.66%) and enriched with Lactobacillus (LDA = 3.63), Acetobacter (LDA = 5.67), and Clostridiales (LDA = 4.21). Red sour soup exhibited higher diversity, with Proteobacteria decreasing to 39.09% and co-existing with multiple other phyla including Chloroflexota (19.72%), and specifically enriched with Akkermansia (LDA = 4.26). Functionally, white sour soup showed higher predicted abundances in host circulatory system (FC = 3.26, p < 0.001) and host immune system (FC = 1.65, p < 0.01) pathways, whereas red sour soup showed higher abundance in the host digestive system pathway (FC = 0.46, p < 0.01). This study systematically reveals, for the first time, raw material-driven bacterial differentiation and provides a theoretical foundation for the functional development of traditional fermented foods.