Application of a Chimeric Protein Construct having Enterotoxin B and Toxic Shock Syndrome Toxin Domains of S. aureus in Immunodiagnostics

Cellular Apoptosis Induced by Deoxynivalenol

Deoxynivalenol (DON) is synthesized by Fusarium species that frequently infect crops during storage, and it's harm risk to human is reflected in the consumption of infected food crops or indirectly through foods of animal origin. In this study, Hela and Chang liver cells were used to research the cellular apoptosis induced by deoxynivalenol. Cells were treated by DON toxin with a series of concentration and incubated for different time. MTT, fluorescence microscope, flow cytometer and Western blot methods were used to analyze the effect of DON on the cell apoptosis in vitro and in vivo systematically. The results showed that DON was toxic to the cells tested. After being treated by DON, the morphology of Chang livers and Hela cells changed significantly. The DON promoted apoptosis in a dose- and time-dependent manner. The activity of Caspase 3 was significantly increased in DON-induced apoptosis. Moreover, endogenous Glutathione (GSH) level in these cell lines was gradually decreased. In the early apoptosis progress, oxidative stress was induced by DON. When DON reached 10 µg/mL, a markedly increased content of Malondialdehyde (MDA) was detected in both Hela and Chang liver cells. Furthermore, an in vivo test indicated that DON had toxicity to mice by causing weight loss and swollen spleen, and significantly increased expression of AST and ALT. In conclusion, the DON was toxic to mice and could induce the apoptosis of tested cells undergoing a Caspase-3 related pathway.

Immunoinformatics analysis and evaluation of recombinant chimeric triple antigen toxoid (r-HAB) against Staphylococcus aureus toxaemia in mouse model

Abstract

Staphylococcus aureus is a serious pathogen unleashing its virulence through several classes of exotoxins such as hemolysins and enterotoxins. In this study, we designed a novel multi-antigen subunit vaccine which can induce innate, humoral and cellular immune responses. Alpha hemolysin, enterotoxins A and B were selected as protective antigens for combining into a triple antigen chimeric protein (HAB). Immunoinformatics analysis predicted HAB protein as a suitable vaccine candidate for inducing both humoral and cellular immune responses. Tertiary structure of the HAB protein was predicted and validated through computational approaches. Docking studies were performed between the HAB protein and mice TLR2 receptor. Furthermore, we constructed and generated recombinant HAB (r-HAB) protein in E. coli and studied its toxicity, immunogenicity and protective efficacy in a mouse model. Triple antigen chimeric protein (r-HAB) was found to be highly immunogenic in mouse as the anti-r-HAB hyperimmune serum was strongly reactive to all three native exotoxins on Western blot. In vitro toxin neutralization assay using anti-r-HAB antibodies demonstrated > 75% neutralization of toxins on RAW 264.7 cell line. Active immunization with r-HAB toxoid gave ~ 83% protection against 2 × lethal dosage of secreted exotoxins. The protection was mediated by induction of strong antibody responses that neutralized the toxins. Passive immunization with anti-r-HAB antibodies gave ~ 50% protection from lethal challenge. In conclusion, in vitro and in vivo testing of r-HAB found the molecule to be nontoxic, highly immunogenic and induced excellent protection towards native toxins in actively immunized and partial protection to passively immunized mice groups.

Key points

• HAB protein was computationally designed to induce humoral and cellular responses.

• r-HAB protein was found to be nontoxic, immunogenic and protective in mouse model.

• r-HAB conferred protection against lethal challenge in active and passive immunization.

Rapid detection of Staphylococcus aureus by loop-mediated isothermal amplification

Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA), is a major bacterial pathogen associated with nosocomial and community-acquired S. aureus infections all over the world. A rapid detection assay for staphylococcal gene of nuc and mecA is needed. In this study, a rapid identification assay based on the loop-mediated isothermal amplification (LAMP) method was established. PCR and LAMP assays were used to detect Staphylococcus aureus and other related species for nuc and mecA. With optimization of the primers and reaction temperature, the LAMP successfully amplified the genes under isothermal conditions at 62 °C within 60 min, of which the results were identical with those of the conventional PCR methods. The detection limits of the LAMP for nuc and mecA were 1.47 and 14.7 pg/μl DNA per tube, respectively, by naked eye inspections, while the detection limits of the PCR for nuc and mecA were 14.7 pg/μl and 147 pg/μl DNA, respectively. Finally, The LAMP method was then applied to clinical blood plaque samples. The LAMP and PCR demonstrated identical results for the plaque samples with the culture assay. Together, the LAMP offers an alternative detection assay for nuc and mecA with a great advantage of the sensitivity and rapidity.