Porcine extraintestinal pathogenic Escherichia coli (ExPEC) is a leading cause of death in pigs and has led to considerable economic losses for the pig industry. Porcine ExPEC infections often cause systemic inflammatory responses in pigs, characterized by meningitis, arthritis, pneumonia, and septicemia. Baicalin has been reported to possess potent anti-inflammatory activity, but its function in porcine ExPEC remains unknown. The aim of this study was to explore the protective effect and mechanism of baicalin against the porcine ExPEC-induced inflammatory responses in 3D4/21 cells. After treatment with baicalin, the effects on cell damage, the level of pro-inflammatory cytokines, the expression of nuclear factor-$\kappa$B (NF-$\kappa$B)/mitogen-activated protein kinase (MAPK) signaling pathways, and the activation of NOD-like receptor protein 3 (NLRP3) inflammasomes were examined. Our results show that baicalin significantly reduced the damage to 3D4/21 cells infected with porcine ExPEC PCN033. Further study showed that baicalin significantly reduced the transcription and expression of pro-inflammatory cytokines such as interleukin-1$\beta$ (IL-1$\beta$), interleukin-6 (IL-6), and interleukin-8 (IL-8). Furthermore, baicalin inhibited the phosphorylation of proteins such as P65, nuclear factor $\kappa$B inhibitor $\alpha$ (I$\kappa$B$\alpha$), extracellular regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and P38 and reduced the expression levels of proteins such as NLRP3, apoptosis-associated speck-like protein containing a CARD (ASC), and caspase-1. These results reveal that baicalin reduced the damage to 3D4/21 cells by inhibiting the expression of NF-$\kappa$B/MAPK signaling pathways and blocking NLRP3 inflammasome activation in 3D4/21 cells infected with porcine ExPEC. Taken together, these results suggest that baicalin may have potential as a medicine for the treatment of porcine ExPEC-infected pigs by regulating inflammatory responses. This study provides a novel potential pharmaco-therapeutic approach to preventing porcine ExPEC infection.

Porcine extraintestinal pathogenic Escherichia coli (ExPEC) is a pathogenic bacterium that causes huge economic losses to the pig farming industry and considerably threatens human health. The quorum sensing (QS) system plays a crucial role in the survival and pathogenesis of pathogenic bacteria. Hence, it is a viable approach to prevent ExPEC infection by compromising the QS system, particularly the LuxS/AI-2 system. In this study, we investigated the effects of baicalin on the LuxS/AI-2 system of ExPEC. Baicalin at concentrations of 25, 50, and 100 μg/mL significantly diminished the survival ability of ExPEC in hostile environments and could inhibit the biofilm formation and autoagglutination ability in ExPEC. Moreover, baicalin dose-dependently decreased the production of AI-2 and down-regulated the expression level of luxS in PCN033. These results suggest that baicalin can weaken the virulence of PCN033 by inhibiting the LuxS/AI-2 system. After the gene luxS was deleted, AI-2 production in PCN033 was almost completely eliminated, similar to the effect of baicalin on the production of AI-2 in PCN033. This indicates that baicalin reduced the production of AI-2 by inhibiting the expression level of luxS in ExPEC. In addition, the animal experiment further showed the potential of baicalin as a LuxS/AI-2 system inhibitor to prevent ExPEC infection. This study highlights the potential of baicalin as a natural quorum-sensing inhibitor for therapeutic applications in preventing ExPEC infection by targeting the LuxS/AI-2 system.

In this study, we found that the deletion of the gene evfG in the type VI secretion system (T6SS) gene cluster significantly affected the motility of porcine extraintestinal pathogenic Escherichia coli (ExPEC) strain PCN033. Furthermore, the bacterial motility assay showed that ΔevfG mutants exhibited reduced motility compared to the parental strain. Transmission electron microscopy (TEM) showed a significant reduction in the number of flagella in the mutant ΔevfG when compared with PCN033. To further explore the reasons why the deletion of evfG affects the motility of PCN033, transcriptomic and metabolomic analyses were conducted. The omics analyses showed that 134 differentially accumulated metabolites and 2236 differentially expressed genes were identified between the mutant ΔevfG and the parental strain PCN033. The metabolome profile and functional annotation analyses indicated that the impaired motility of ΔevfG was connected to the downregulation of the expression levels of genes associated with the energy metabolism pathway and flagellar assembly. Our study provides a new insight into the diminished PCN033 motility induced by evfG deletion. Moreover, the candidate genes and metabolites regulated by the gene evfG in the T6SS, which was involved in the motility of PCN033, were reported in this study.

The gut microbiota is engaged in multiple interactions affecting host health, and gut dysbiosis can lead to many diseases. However, the effects of acetylcysteine (NAC) on the gut microbiome composition in pigs using metagenomic sequencing have not been reported. In this study, we used metagenome sequencing to study the effects of NAC on the pig gut microbiome. Sequencing results showed that microbial diversity was changed after NAC treatment. Antibiotic Resistance Genes Database (ARDB) analysis demonstrated that the main genes modified were macb, tsnr, norm, bl2be-per, vansb and pbp1b in the NAC group. Our data showed that NAC could affect microbial distribution at the phylum, gene and species levels. At the species level, NAC significantly increased the abundances of Megasphaera, Lactobacillus reuteri and Megasphaeraelsdenii and reduced the abundances of Phascolarctobacterium succinatutens, Prevotellacopri and Selenomonasbovis compared with the control group. In addition, Gene Ontology (GO) analysis revealed that in the NAC group, cellular process, metabolic process and single-organism process were the dominant terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis demonstrated that RNA transport, MAPK signaling pathway, cell cycle, glycosylphosphatidylinositol (GPI)-anchor biosynthesis and VEGF signaling pathway were the dominant signaling pathways in the NAC group. In conclusion, our results suggest that NAC may modify the piglet gut microbiome composition and these findings might provide a new strategy for maintaining animal and human health in the future.