Extraction and Electrophoretic Analysis of Bacterial Lipopolysaccharides and Outer Membrane Proteins

Immunogenicity of Brucella Trivalent Immunogen-Containing Polyethyleneimine Nanostructure Targeted with LPS in a Mouse Model

Brucella is a facultative intracellular gram-negative coccobacillus. It is nonsporulating and reproduced in macrophage phagosomes. The use of nanostructures as drug and vaccine carriers has recently received attention due to their ability to control the release profile and protect the drug molecules. This study presents a suitable nano-polyethyleneimine formulation to be used as an immunoadjuvant and LPS along with trivalent candidate antigens of TF, BP26, and omp31 to selectively stimulate the immune response. After designing and evaluating the immunogenic structure by databases and bioinformatics software, recombinant protein cloning and gene expression were performed in Escherichia coli BL21 bacteria. This protein was extracted from the cultured cells, purified by Ni-NTA column. After placing the antigen inside the polyethyleneimine nanostructure, various properties of the nanoparticles, including their size, zeta potential, and retention rate for injection and inhalation of mice, diffusion efficacy, and antigen binding evaluation were evaluated. Mice were treated with different groups of antigens and nanoparticles on days 0, 10, 24, and 38. Two weeks after the last injection, the level of cytokines were investigated in spleen cells, including IFN-γ, IL-4, and IL-12. The serum concentration of IgG2a and IgG1 antibodies were also assessed. The response was consistent with significant production of IgG1, IgG2a, IFN-γ21, IL-12, and IL-4 compared to the controls (P < 0.05). Compared to the positive and negative control groups, recombinant protein and nanoparticles showed a good response in subsequent injections with live bacterial strains. The present study also revealed the potential of the developed recombinant protein as a candidate in the design and manufacture of subunit vaccines against Brucella species. This protein stimulates cellular and humoral immune responses compared to the positive control groups. These findings can be useful in the prevention and control of brucellosis and pave the way for further research by researchers around the world.

RfaH contributes to maximal colonization and full virulence of hypervirulent Klebsiella pneumoniae

Hypervirulent K. pneumoniae (hvKp) have emerged as clinically important pathogens, posing a serious threat to human health. RfaH, a transcriptional elongation factor, has been regarded as implicated in facilitating the transcription of long virulence operons in certain bacterial species. In K. pneumoniae, RfaH plays a vital role in promoting CPS synthesis and hypermucoviscosity, as well as mediating bacterial fitness during lung infection. In this study, we aim to conduct a systematic investigation of the roles of rfaH in the survival, dissemination, and colonization of hvKp through in vitro and in vivo assays. We found that bacterial cells and colonies displayed capsule -deficient phenotypes subsequent to the deletion of rfaH in K. pneumoniae NTUH-K2044. We confirmed that rfaH is required for the synthesis of capsule and lipopolysaccharide (LPS) by positively regulating the expression of CPS and LPS gene clusters. We found that the ΔrfaH mutant led to a significantly decreased mortality of K. pneumoniae in a mouse intraperitoneal infection model. We further demonstrated that the absence of rfaH was associated with slower bacterial growth under conditions of low nutrition or iron limitation. ΔrfaH displayed reduced survival rates in the presence of human serum. Besides, the engulfment of the ΔrfaH mutant was significantly higher than that of NTUH-K2044 by macrophages in vivo, indicating an indispensable role of RfaH in the phagocytosis resistance of hvKp in mice. Both mouse intranasal and intraperitoneal infection models revealed a higher bacterial clearance rate of ΔrfaH in lungs, livers, and spleens of mice compared to its wild type, suggesting an important role of RfaH in the bacterial survival, dissemination, and colonization of hvKp in vivo. Histopathological results supported that RfaH contributes to the pathogenicity of hvKp in mice. In conclusion, our study demonstrates crucial roles of RfaH in the survival, colonization and full virulence of hvKp, which provides several implications for the development of RfaH as an antibacterial target.

Characterization of Histophilus somni sialic acid uptake mutant (ΔnanP-ΔnanU) using a mouse septicemia and mortality model

Histophilus somni is an important pathogen of the bovine respiratory disease complex, yet the mechanisms underlying its virulence remain poorly understood. It is known that H. somni can incorporate sialic acid into lipooligosaccharide (LOS), and sialylated H. somni is more resistant to phagocytosis and complement-mediated killing by serum compared to non-sialylated bacteria in vitro. However, the virulence of non-sialylated H. somni has not been evaluated in vivo using an animal model. In this study, we investigated the contribution of sialic acid to virulence by constructing an H. somni sialic acid uptake mutant (ΔnanP-ΔnanU) and comparing the parent and mutant strains in a mouse septicemia and mortality model. Intraperitoneal challenge of mice with wildtype H. somni (1 × 108 colony forming units/mouse, CFU) was lethal to all animals. Mice challenged with three different doses (1, 2, or 5 × 108 CFU/mouse) of an H. somni ΔnanP-ΔnanU sialic acid uptake mutant exhibited survival rates of 90 %, 60 %, and 0 % respectively. High-performance anion exchange chromatography analyses revealed that LOS prepared from both parent and the ΔnanP-ΔnanU mutant strains of H. somni were sialylated. These findings suggest the presence of de novo sialic acid synthesis pathway, although the genes associated with de novo sialic acid synthesis (neuB and neuC) were not identified by genomic analysis. The lower attenuation in mice is most likely attributed to the sialylated LOS of H. somni nanPU mutant.

Enhanced phagocytosis and complement-mediated killing of Mannheimia haemolytica serotype 1 following in-frame CMP-sialic acid synthetase (neuA) gene deletion

IMPORTANCE

The Gram-negative coccobacillus Mannheimia haemolytica is a natural inhabitant of the upper respiratory tract in ruminants and the most common bacterial agent involved in bovine respiratory disease complex development. Key virulence factors harbored by M. haemolytica are leukotoxin, lipopolysaccharide, capsule, adhesins, and neuraminidase which are involved in evading innate and adaptive immune responses. In this study, we have shown that CMP-sialic acid synthetase (neuA) is necessary for the incorporation of sialic acid onto the membrane, and inactivation of neuA results in increased phagocytosis and complement-mediated killing of M. haemolytica, thus demonstrating that sialylation contributes to the virulence of M. haemolytica.