With the prohibition of antibiotics in animal feed, the livestock industry faces significant challenges, including increased morbidity and mortality rates and reduced farming efficiency. Developing green, natural, and safe antibiotic alternatives has become a research hotspot. This study evaluated the effects of octapeptin as a feed additive on growth performance, diarrhea incidence, serum biochemistry, serum immune factors, and gut microbiota of weaned piglets. Seventy-two weaned piglets were randomly assigned to three groups based on body weight and sex, with each group receiving different dietary treatments: a negative control group (CON, basal diet), a positive control group (MC, basal diet + 5 mg/kg Microcin C7), and an octapeptin supplement group (OP, basal diet + 40 mg/kg octapeptin). After 28 days of feeding experimental diets, the results demonstrated that supplementing the diet of weaned piglets with octapeptin significantly improved the feed conversion ratio compared to the control group (p < 0.05) over the entire experimental period. Furthermore, a reduction in diarrhea incidence was observed during the late nursery period (14–28 d), resulting in an overall improvement in diarrhea compared to the other two groups (p < 0.01). Serum biochemical analysis results revealed a trend towards decreased alanine aminotransferase level in the octapeptin group, with no significant differences in other indicators, suggesting potential improvements in liver function without causing liver damage. In addition, compared to the control group, octapeptin enhanced mucosal immunity by decreasing TNF-α level (p < 0.05). Fecal microbiota analysis results showed a significant increase in beneficial bacteria such as Collinsella and Olsenella in the octapeptin group compared to the other two groups (p < 0.05), indicating a positive impact on gut health. These findings supported the potential of octapeptin as an alternative to antibiotic growth promoters in weaned piglets’ diets.

The interaction forces and mechanical properties of the interaction between melittin (Mel) and lipopolysaccharide (LPS) are considered to be crucial driving forces for Mel when killing Gram-negative bacteria (GNB). However, how their interaction forces perform at the single-molecule level and the dissociation kinetic characteristics of the Mel/LPS complex remain poorly understood. In this study, the single-molecule-level interaction forces between Mel and LPSs from E. coli K-12, O55:B5, O111:B4, and O128:B12 were explored using atomic force microscopy (AFM)-based single-molecule force spectroscopy (SMFS). AFM-based dynamic force spectroscopy (DFS) and an advanced analytical model were employed to investigate the kinetic characteristics of the Mel/LPS complex dissociation. The results indicated that Mel could interact with both rough (R)-form LPS (E. coli K-12) and smooth (S)-form LPSs (E. coli O55:B5, O111:B4, and O128:B12). The S-form LPS showed a more robust interaction with Mel than the R-form LPS, and a slight difference existed in the interaction forces between Mel and the diverse S-form LPS. Mel interactions with the S-form LPSs showed greater specific and non-specific interaction forces than the R-form LPS (p < 0.05), as determined by AFM-based SMFS. However, there was no significant difference in the specific and non-specific interaction forces among the three samples of S-form LPSs (p > 0.05), indicating that the variability in the O-antigen did not affect the interaction between Mel and LPSs. The DFS result showed that the Mel/S-form LPS complexes had a lower dissociation rate constant, a shorter energy barrier width, a longer bond lifetime, and a higher energy barrier height, demonstrating that Mel interacted with S-form LPS to form more stable complexes. This research enhances the existing knowledge of the interaction micromechanics and kinetic characteristics of Mel and LPS at the single-molecule level. Our research may help with the design and evaluation of new anti-GNB drugs.

The interaction forces and mechanical properties of the interaction between melittin (Mel) and lipopolysaccharide (LPS) are considered a crucial driving force for Mel in killing Gram−negative bacteria (GNB). However, how their interaction forces are performed at the single−molecule level and the dissociation kinetic characteristics of the Mel/LPS complex remain poorly understood. In this study, the single−molecule level interaction forces between Mel and LPSs from E. coil K−12, O55:B5, O111:B4, and O128:B12 were explored using atomic force microscopy (AFM) based single−molecule force spectroscopy (SMFS). Further, the AFM−based dynamic force spectroscopy (DFS) and advanced analytical model were employed to investigate the kinetic characteristics of the Mel/LPSs complex dissociation. The results indicated that Mel could interact with both rough (R)−form LPS (E. coli K−12) and smooth (S)−form LPSs (E. coli O55:B5, O111:B4, O128:B12), and the S−form LPSs showed a more robust interaction with Mel than R−form LPS, and a slight difference existed in the interaction forces between Mel and diverse S−form LPSs. The Mel interacts with S−form LPSs showed greater specific and non−specific interaction forces than R−form LPS (p < 0.05), as determined by AFM−based SMFS. However, there was no significant difference in the specific and non−specific interaction forces among the three S−form LPSs (p > 0.05), indicating the variability of O−antigen could not affect the interaction between Mel and LPSs. The DFS result showed that the Mel/S−form LPSs complexes had a lower dissociation rate constant (koff), a shorter energy barrier width (xβ), a longer bond lifetime (τoff), and a higher height of the energy barrier (∆G), demonstrating that Mel could interact with S−form LPSs to form more stable complexes. In conclusion, this study promotes our knowledge of the interaction micromechanics and kinetics characteristics between Mel and LPS at the single−molecule level. Moreover, it can help us design and evaluate new anti−GNB drugs.