Salmonella is a foodborne pathogen that causes enterogastritis among humans, livestock and poultry, and it not only causes huge economic losses for the feed industry but also endangers public health around the world. However, the prevention and treatment of Salmonella infection has remained poorly developed because of its antibiotic resistance. Bacterial quorum sensing (QS) system is an intercellular cell–cell communication mechanism involving multiple cellular processes, especially bacterial virulence, such as biofilm formation, motility, adherence, and invasion. Therefore, blocking the QS system may be a new strategy for Salmonella infection independent of antibiotic treatment. Here, we have reviewed the central role of the QS system in virulence regulation of Salmonella and summarized the most recent advances about quorum quenching (QQ) in virulence attenuation during Salmonella infection. Unraveling the complex relationship between QS and bacterial virulence may provide new insight into the therapy of pathogen infection.

Escherichia coli is a leading cause of bovine mastitis worldwide. The bacteria can rapidly grow in milk and elicit a strong lipopolysaccharide (LPS)/toll-like receptor-4 (TLR4)-dependent inflammatory response. Recently, the long polar fimbriae (LPF) were identified as a promising virulence factor candidate widely distributed in mammary pathogenic E. coli (MPEC) strains. Mammary pathogenic E. coli possess 2 lpf loci encoding LPF1 and LPF2, respectively. By deleting the major fimbrial subunit gene, lpfA, we found that both LPF1 and LPF2 contribute to MPEC adhesion, invasion, and biofilm formation in vitro. The lpf1A and lpf2A mutants showed reduced cytotoxicity in our in vitro cell infection model. Furthermore, we observed that LPF2 induced a mild TLR4-independent proinflammatory response. The median lethal dose (LD50) of both ∆lpf2A and ∆lpf1A∆lpf2A mutants to BALB/c mice increased by 0.38 and 0.15 logs, respectively, whereas that of wild-type strain MPJS13 was 8.69 logs. In contrast, LPF1 deficiency significantly enhanced the LPS/TLR4-mediated inflammatory response in mammary epithelial cells, and the LD50 of the mutant decreased to 8.18 logs. In conclusion, our data suggested that LPF are important in MPEC colonization of mammary cells and may provide a benefit to bacterial intracellular survival that induces persistent bovine mastitis.

Pullorum disease caused by Salmonella Pullorum is one of the most important infectious diseases in the poultry industry worldwide, which leads to serious economic losses in many developing countries because of its high mortality rate in young chicks. The traditional slide agglutination test with low cost, fast reaction, and on-site detection has been widely used in the diagnosis of Pullorum disease. However, in practice, the test performance is with the disadvantages of false positive results and unstable detection results. In this paper, we developed self-made agglutination antigens prepared by local isolates in the poultry farm and compare the detection performance with commercial agglutination antigens (China Institute of Veterinary Drug Control) and Group D Salmonella ELISA kit (BioChek UK Ltd). The results of detecting 200 serum samples indicated that the consistency of commercial agglutination antigen detecting in 2 times was only 79.5%. Using the ELISA kit as the reference method, the commercial agglutination antigen detecting results of the Kappa test were only moderately consistent (0.58 ∼ 0.59). Meanwhile, positive and total coincidence rates of the self-made agglutination antigen test with more reliable repeat could reach 97.4 and 88%, respectively, and the result of Kappa test was highly consistent (0.75). The Receiver Operating Characteristic curve analysis clarified that the area under the receiver-operating-characteristic curve values of self-made and commercial agglutination antigen tests could reach 0.861 and 0.804, respectively. These results were coincident when detecting known positive serum from the infected chickens. It's worth mentioning that the visible positive reaction of self-made agglutination antigen test appeared faster and stronger than commercial antigen test. In conclusion, self-made Salmonella Pullorum agglutination antigen developed in this study was much better than commercial agglutination antigen and is expected to be a valuable tool in the diagnosis of the epidemiology of Salmonella Pullorum.

Klebsiella pneumoniae, a zoonotic pathogen of global concern, poses significant threats to both veterinary and public health. Here, a comparative study characterized 14 clinical isolates (7 avian-derived, 7 human-derived) from Jiangsu, China, through integrated genomic and phenotypic analyses. Firstly, multilocus sequence typing (MLST) revealed distinct epidemiological patterns: the same ST type in avian isolates was circulating between different species and different regions, whereas it was not found in human isolates. In addition, hypervirulent Klebsiella pneumoniae (hvKP) phenotypes confirmed by string test were exclusive to two human isolates (KP15, KP20). Secondly, biofilm detection demonstrated 78.6% (11/14) of isolates possessed biofilm-forming capacity, with cellulose but not curli as the predominant matrix component. Human-derived KP15 and KP20 had the strongest biofilm formation ability in all isolates. Antimicrobial susceptibility profiling identified serious multidrug resistance in both avian and human isolates. Virulence gene analysis revealed striking disparities, with human isolates harboring 10–20 virulence factors (median 15) versus 6–7 (median 6.5) in avian counterparts. Finally, functional pathogenesis assessments demonstrated human-derived strains exhibited stronger epithelial cell adhesion (2-fold higher) and invasion (1.97-fold higher) in Calu-3 cell models and paradoxically showed reduced macrophage phagocytosis (2.85-fold lower at 2 h) for immune escape. In vivo models confirmed dose-dependent mortality, with human isolates demonstrating higher lethality in both Galleria mellonella and mice. Virulence gene burden positively correlated with mortality outcomes. These findings delineate critical host adaptation differences in Klebsiella pneumoniae populations and provide empirical evidence for pathogen transmission dynamics at the human-animal interface.